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Resolution 235-2015 2 of 3 Nfri4. . � •► ',- E. le,-'O' .4400..' i Pt / :,, r + � f i ' await NC 6- Z •Iles _ ... ��. tlt Coastal Manual Principles and Practices of Planning, Siting, Designing, Constructing, and Maintaining Residential Buildings in Coastal Areas (Fourth Edition) FEMA P-55 / Volume II / August 2011 EpART,y �F " FEMA _.1,D SEA } Coastal Manual Principles and Practices of Planning, Siting, Designing, Constructing, and Maintaining Residential Buildings in Coastal Areas (Fourth. Edition) FEMA P-SS / Volume II / August 2011 509) FEMA 'qND Sti All illustrations in this document were created by FEMA or a FEMA contractor unless otherwise noted. All photographs in this document are public domain or taken by FEMA or a FEMA contractor,unless otherwise noted. Volume II DESIGNING THE BUILDING 9 9.1.6 Wall to Floor Framing (Link #6) Link#6 is the connection of the wall framing to the floor framing (see Figures 9-6 and 9-15) for resistance to wind uplift. This connection often includes use of metal connectors between the wall studs and the band joist or wood structural panel sheathing. In,addition to uplift, connections between wall and floor framing can be used to maintain the load path for out-of-plane wall forces from positive and negative wind pressures and forces in the plane of the wall from shear. One method of sizing the wind uplift and lateral connections between the wall framing and the floor framing is provided in Example 9.4. Figure 9-15. Wall studs Connection of wall to floor framing(Link#6) �II Er • • Bottom plate 41'// ! Band joist Two-member floor support LQ ®.® -" beam --awillgt Link#6 Pile a EXAMPLE 9.4. UPLIFT AND LATERAL LOAD PATH AT WALL-TO-FLOOR FRAMING Given: . . .. ,, . . . ... • Refer to Figure 9-15 j • Unit uplift load at top of wall565:2 plf(from Example 9.2) • Unit lateral load= 241.9.plf(from Example . • Wall dead load = 10 psf • Wall height= 10 ft Wood specific gravity, G 0.42 i • Three 16d common stud-to-plate rails.per stud to provide resistance to lateral loads • Two 16d common plate-to-band joist nails per ft to provide resistance to lateral loads COASTAL CONSTRUCTION MANUAL 9-15 9 DESIGNING THE BUILDING Volume II EXAMPLE 9.4. UPLIFT AND LATERAL LOAD PATH AT WALL-TO-FLOOR FRAMING (concluded) Find: . . • Uplift load for wall-to-floor framing connections and if framing connections are adequate to resist the lateral loads. Solution: Determine the uplift and lateral load for the wall-to-floor framing connections as follows: . . Uplift.•. . Wall dead load= (10 psf)(10-ft wall height) = 100 plf Uplift load at top of wall = 565.2 plf Uplift load at the base of the wall = 565.2 plf-0.6(100 plf) = 505.2 plf where: 0.6=load factor on dead load used to resist uplift forces For connectors spaced at 16 in. o.c., the minimum uplift load per connector is: Uplift load per connector= (505.2 plf) 16 in. = 674 lb 12 in./ft Lateral: • Stud-to-plate nail resistance to lateral loads can be calculated as: Lateral resistance = (3 nails/ft)(120 lb/nail)(1.6)(0.67) = 386 lb where: . . 1.6=NDS load duration factor 0.67=NDS end grain factor Because studs are at 16 inches o.c., unit lateral load resistance is: Lateral resistance= (386 lb)12 in./ft_ 289 lb 16 in. 289 plf> 241.9 plf✓ • Plate-to-band joist nail resistance to lateral can be calculated as: Lateral resistance = (2 nails/ft)(120 lb/nail)(1.6) = 384 plf where: 1.6 =NDS load duration factor 384 plf> 241.9 plf✓ '. The wall-to-floor framing connections provide adequate resistance to lateral forces. 9-16 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9 9.1.7 Floor Framing to Support Beam (Link #7) Link #7 is the connection between the floor framing and the floor support beam (see Figures 9-6, 9-16, 9-17, and 9-18). The connection transfers the uplift forces that are calculated in Example 9.4. Options for maintaining the uplift load path for wind uplift include using metal connectors (see Figures 9-16 and 9-17) between the floor joist and the band joist or wood blocking(see Figure 9-18). Connections are also necessary to maintain a load path for lateral and shear forces from the floor and wall framing into the support beam. One method of sizing the wind uplift connections between the floor framing and support beam is provided in Example 9.5. Figure 9-16. Band joist Floor framing Connection of floor ��/// framing to support beam Floor joistIrr /s' (Link#7) (band joist ,// nailing to the floor joist is (. .j r• v �' adequate to resist uplift �� it�r�'. ;j !,;>,� forces) dr. i & : °) Of 111 Link#7 ®: 1 -le is. Two-member Pile floor support beam Z' 4` .rk4\'4 - Figure 9-1 7. ,, �� • , • ,, 4 >>, Metal joist-to-beam o-beam • ' a ` ' ' connector . pNeNi ' � ` ,,. N #r j r Jr i \1/4 pe A .z -ey - I l a��-,- ..pp .:,......:::„.............r..................r.:.• COASTAL CONSTRUCTION MANUAL 9-17 9 DESIGNING THE BUILDING Volume II -- EXAMPLE 9.5. UPLIFT LOAD PATH AT FLOOR TO SUPPORT BEAM FRAMING Given: • Refer to Figure 9-16 • Unit uplift load at top of wall 565.2 plf(from Example 9.2) • Wall dead load= 10 psf . • Floor dead load = 10 psf • Wall height= 10 ft . . Find: • Uplift load for floor framing to beam connections . . Solution: The uplift load for the floor framing to beam connections can be determined as follows: Uplift. Wall dead load= (10 psf)(10 ft wall height) = 100 plf Floor dead load =. 10 psf 1 Zft= 70 plf. Uplift load at the base of the floor= 565.2 plf—0.6 (100 plf+ 70 plf) =-463.2 plf where: 0.6 =load factor on dead load used to resist uplift forces For connectors spaced at 16 in. o.c., the minimum uplift load per connector is: 16 in. Uplift load per connector= (463.2 plf) = 618lb 12 in./ft 9.1.8 Floor Support Beam to Foundation (Pile) (Link#8) Link #8 is the connection of the floor support beam to the top of the pile (see Figures 9-6 and 9-18). Link#8 resists wind uplift forces, and the connection often consist of bolts in the beam-to-pile connection or holddown connectors attached from wall studs above to the pile. One method of sizing the wind uplift connections between the floor support beam and piles is provided in Example 9.6. The connection of the beam to the pile is also designed to maintain load path for lateral and shear forces. It is typically assumed that lateral and shear forces are transferred through the floor diaphragm and can therefore be distributed to other support beam-to-pile connections. Stiffening of the diaphragm can be achieved by installing braces at each corner pile between the floor support beam in the plane of the floor (see Figure 9-19) or sheathing the underside of the floor framing. Stiffening also reduces pile cap rotation. The load path, however, does not end at Link#8. The load path ends with the transfer of loads from the foundation into 9-18 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9 the soil. See Chapter 10 for considerations that must be taken into account with regard to the interaction between the foundation members and soil in the load path. Figure 9-18. Wall studs Connection of floor support beam to foundation (Link#8) 1 • : Bottom plate Al Band joist Two-member floor supportitY beam #8 ��Pile 4014, :,de EXAMPLE 9.6. UPLIFT LOAD PATH FOR SUPPORT BEAM TO PILE Given: • Refer to Figure 9-18 • Unit uplift load at top of floor beams = 463.2 plf(from Example 9.5) • Pile spacing=.9.33 ft • Continuous beam of 28-ft.length at end wall • ASD capacity for 1-in. diameter bolt in beam-to-pile connection = 1,792 lb (where wood specific gravity (G) = 0.42, 3.5-in. side member, and 5.25-in. main member Find: 1. Uplift load for support beam-to-pile connections. 2. Number of bolts required for support beam-to-pile connections for wind uplift. Solution for #1: The.uplift load for the support beam-to-pile connections can be determined as follows: Upl ft Tributary length of center pile connection = 9.33 ft COASTAL CONSTRUCTION MANUAL 9-19 9 DESIGNING THE BUILDING Volume II EXAMPLE 9.6. UPLIFT LOAD PATH FOR SUPPORT BEAM-TO-PILE (concluded) Uplift load at center pile connection= (9.33 ft)(463.2 plf)=4,322 lb Tributary length of end pile connection=,9.33 ft =4.67 ft Uplift load at end pile connection = (4.67 ft)(463.2 plf) =2,163 lb Solution for #2: The number of bolts required for the support beam-to-pile connections can be determined as follows: Connection at center pile (number of bolts) = Connection at center pile (number of bolts) 4,322 lb =2.41 bolts= 1,792lb/bolt 3 bolts at support beam-to-pile connection Connection at end pile (number of bolts)= 2,163 lb =1.21 bolts= 1,792 lb/bolt 2 bolt at support beam-to-pile connection Figure 9-19. Diaphragm stiffening and 2x floor joist material or sheathing screwed 16 inches on center corner pile bracing to into bottoms of joists (typical) reduce pile cap rotation / Floor a A joists C m E A oc A `aco , Floor support beam Band joist 9.33 feet 2x joist #12 3-inch-long galvanized or 2x joist material stainless steel screws,3 per joist or sheathing per board(typical) Section A-A 9-20 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9 9.2 Other Load Path Considerations Several additional design considerations must be investigated in order for a design to be complete.The details of these investigations are left to the designei, but they are mentioned here to more thoroughly cover the subject of continuous load paths and to point out that many possible paths require investigation. Using the example of the building shown in Example 9.3, Illustration A, the following load paths should also be investigated: ✓ Load paths for shear transfer between shear walls and diaphragms including uplift due to shear wall overturning L Gable wall support for lateral wind loads • Uplift of the front porch roof Li Uplift of the main roof section that spans the width of the building Other factors that influence the building design and its performance are: • Connection choices O Building eccentricities c Framing system E. Roof shape 9.2.1 Uplift Due to Shear Wall Overturning The shear wall that contains Link#6 includes connections designed to resist overturning forces from wind acting perpendicular to the ridge (see Example 9.7, Illustration A). Calculation of the overturning induced uplift and compressive forces are given in Example 9.7. t. as EXAMPLE 9.7. UPLIFT AND COMPRESSION DUE TO SHEAR WALL OVERTURNING • Given: .•.=Refer to Illustration A { • Wind speed = 150 mph,Exposure D • Mean roof height 33 ft • Roof span perpendicular to ridge=,28 ft • Roof pitch = 7:12 • Wall height= 10.ft COASTAL CONSTRUCTION MANUAL 9-21 9 DESIGNING THE BUILDING Volume II EXAMPLE 9.7. UPLIFT AND COMPRESSION DUE TO SHEAR WALL OVERTURNING (continued) Wind or seismic a 7,175 lb i Eaft � `. 6;ft 4aft ) o I \ / \ / \ / " 4'"� b 4 — b 4 '� b C V T C v T C V T o =Shearwall ❑ =Sheathing Holddown connector C =Compression force T =Tension force V =Shear force ❑ =Portion of wall not designed to provide resistance to shear loads Illustration A. Loads on south shear wall Find: Uplift and compressive force due to shear;wall overturning. Solution: The uplift and compressive force due to shear wall overturning can be determined as follows: • The total shear force due to wind acting perpendicular to the ridge is determined for.the 28-ft roof span by interpolation from Table 8-7: Roof diaphragm load for 24-fr roof span = 256 plf Roof diaphragm load for 32-ft roof span= 299 plf I (256 plf+299 plf)Roof diaphragm load for 28-ft roof span= - 2 =278 plf Adjusting the roof diaphragm load to account for the building being located in Exposure Category D: 1.18(278 plf) = 328 plf:. To adjust W ooffor a wall height of 10 ft because Table 8.7 assumes a wall height.of 8 ft 10ft 328 plf 410 plf 8ft 9-22 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9 EXAMPLE 9.7..UPLIFT AND COMPRESSION DUE TO SHEAR WALL OVERTURNING , (concluded).. • The total shear load for south wall assuming flexible diaphragm distribution of roof diaphragm load is-calculated as follows: Length tributary to shear walls= 35 ft =17.5 ft (see Example 9.3, Illustration A) 2 . Shear load in south shear walls = (17.5 ft)(410 plf) = 7,175 lb Shear wall segment aspect ratio (see Illustration B): • Each shear wall segment must meet the requirements for shear wall aspect ratio in order to be considered as:a shear resisting element. For wood structural panel shear walls, the maximum ratio of height to length (e.g., aspect ratio, h/L) is 3.5:1. • • The aspect ratio for shear wall segments in Illustration A can be calculated as follows: loft Aspect ratio of 6-ft long shear wall segment =1.67< 3.5✓ .. Eft 10 ft Aspect ratio of 3-ft long shear all segment: =3.33.< 3.5✓ 3.ft. . . 7,1751b Unit shear, v= total shear load/shear wall length = =598 plf (6 ft+3 ft+3 ft) Uplift(7) and compressive force (C) at shear wall ends due to overturning = (598 plf)(10-ft wall height) =5,980lb "Note:As seen in this example, tension and 'compression forces due to shear wall overturning can be large. Alignment of shear wall end posts with piles below facilitates use of standard connectors and manufacturers' allowable design values..A.check of the pile!uplift and compressive capacity in soil is needed to ensure an adequate load path for overturning forces. Because of the magnitude of overturning induced uplift and compression forces, it is desirable to align shear wall ends with piles to provide direct vertical support and to minimize offset of the tension or compression load path from the axis of the pile. Where shear wall end posts are aligned with piles below, detailing that allows connection of the shear wall end post holddown directly to the pile is desirable to minimize forces transferred through other members such as the support beams.Where direct transfer of overturning induced uplift and compression forces into the pile is not possible, minimizing the offset distance reduces bending stresses in the primary support beam (see Figure 9-20). For the holddown connection shown in Figure 9-20, the manufacturers' listed allowable load will be reduced because the bolted connection to the wood beam is loaded perpendicular to grain rather than parallel to grain. COASTAL CONSTRUCTION MANUAL 9-23 9 DESIGNING THE BUILDING Volume II Figure 9-20. - Shear wall holddown , connector with bracket �' - i i N,,--- attached to a wood beam - J- - ,,. '-jilliVit€ a .t V 011114', /V - . .,-.- ''''., ' - 4 ' i I v7a.ji I .01011 till. ill, ____,.._ NM! r,L, 9.2.2 Gable Wall Support There are many cases of failures of gable-end frames during high-wind events. The primary failure modes in gable-end frames are as follows: A gable wall that is not braced into the structure collapses, and the roof framing falls over (see Figure 9-21) An unsupported rake outrigger used for overhangs is lifted off by the wind and takes the roof sheathing with it The bottom chord of the truss is pulled outward, twisting the truss and causing an inward collapse The need for and type of bracing at gable-end frames depend on the method used to construct the gable end. Recommendations for installing rafter outriggers at overhangs for resistance to wind loads are provided in the Wood Frame Construction Manual(American Wood Council, 2001). In addition to using the gable-end truss bracing shown in Figure 9-22,installing permanent lateral bracing on all roof truss systems is recommended. Gable-end trusses and conventionally framed gable-end walls should be designed, constructed, and sheathed as individual components to withstand the pressures associated with the established basic wind speed. 9.2.3 Connection Choices _ CROSS REFERENCE , Alternatives for joining building elements include: For recommendations on Mechanical connectors such as those available from a corrosion-resistant connectors, variety of manufacturers see Table 1 in NFIP Technical Bulletin 8, Corrosion Protection for Metal Connectors in Coastal Fasteners such as nails, screws, bolts, and reinforcing steel Areas (FEMA 1996). 9-24 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9 Figure 9-21. Gable-end failure, Hurricane Andrew(Dade County, FL, 1992) • !O . 1 , �f•} V-j_• {-: • L r • am. Jay'f;�tir�'�`�( YI�j/' ]I/lfj' E Connectors such as wood blocks u Alternative materials such as adhesives and strapping Most commercially available mechanical connectors recognized in product evaluation reports are fabricated metal devices formed into shapes designed to fit snugly around elements such as studs, rafters, and wall plates. To provide their rated load, these devices must be attached as specified by the manufacturer. Mechanical connectors are typically provided with various levels of corrosion resistance such as levels of hot-dip galvanizing and stainless steel. Hof-dip galvanizing may be applied before or after fabrication. Thicker galvanized coatings can consist of 1 to 2 ounces of zinc per square foot. Thicker coatings provide greater protection against corrosion. Welded,steel products generally have a hot-dip galvanized zinc coating or are painted for corrosion protection. Stainless steel (A304 and A316) connectors also provide corrosion resistance. Because exposed metal fasteners (even when galvanized) can corrode in coastal areas within a few years of installation, stainless steel is recommended where rapid corrosion is expected. According to FEMA NFIP Technical Bulletin 8-96, the amount of salt spray in the air is greatest near breaking waves and declines with increasing distance away from the shoreline. The,decline may be rapid in the first 300 to 3,000 feet. FEMA P-499 recommends using stainless steel within 3,000 feet of the coast (including sounds and back bays). Metal connectors must be used in accordance with the manufacturer's installation instructions in order for the product to provide the desired strength rating and to ensure that the product is suitable for a particular application. Particular attention should be given to the following information in the installation instructions: c Preservative treatments used for wood framing Level of corrosion protection Li Wood species or lumber type used in framing(e.g., sawn lumber, pre-fabricated wood I-joists, laminated veneer lumber) COASTAL CONSTRUCTION MANUAL 9-25 • 9 DESIGNING THE BUILDING Volume II Gable-end truss II 2x4 Brace 2x Ladder framing -'-- -. I. Metal strap2x4 Blo/tf4 ...._ ,...... i 410 1 . 0,,,„ --ftr..... , Ir/ 2x4x8 feet Braces extend to 0 Brace fourth truss No roof sheathing joints parallel to gable-end eave F Roof sheathing nails at 4 inches X XTh X o.c. maximum IX )1/4 o 2x Ladder framing-J Gable-end truss Engineered wood 2x4 continuous at 24 inches o.c. designed for roof trusses at brace maximum end-wall pressure 24 inches o.c. maximum I 2x4x8 feet long Exterior-----� Metal strap brace at 5 feet structural 4 inches o.c. sheathing maximum —j� y l 2—10d nails at T X X each truss 2—2x4 w 1 nails s 2x4 blocking 2x6 / Od a s top plate�� at 12 inches o.c.to betweenE----- Interior finish Stud wall double top plate trusses and sheathing Section A-A —11r— Figure 9-22. Gable-end bracing detail; nailing schedule, strap specification, brace spacing, and overhang limits should be adapted for the applicable basic wind speed 9-26 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9 L-7 Rated capacity of connector for all modes of failure (e.g., shear, uplift, gravity loading) Level of corrosion protection for nails, bolts, and/or screws r• Nail, bolt, and/or screw size and type required to achieve rated loads 9.2.4 Building Eccentricities The L-shaped building configuration produces stress concentrations in the re-entrant corner of the building structure. Additionally, differences between the center of rotation and the center of mass produce torsional forces that must be transferred by the diaphragms and accounted for in the design of shear walls. Provisions for torsional response are different for wind and seismic hazards. Design methods to account for building eccentricities is beyond the scope of this Manual;therefore,the user is referred to building code requirements and provisions of ASCE 7-10 and applicable material design standards. 9.2.5 Framing System Methods used for maintaining a load path throughout the structure depend on the framing system or structural system that makes up the building structure. Specifics related to platform framing, concrete/ masonry construction, and moment-resistant framing are provided below. 9.2.5.1 Platform Framing Across the United States, platform framing is by far the most common method of framing a wood-stud or steel-stud residential building. In the platform framing method, a floor assembly consisting of beams,joists, and a subfloor creates a "platform" that supports the exterior and interior walls. The walls are normally laid out and framed flat on top of the floor,tilted up into place,and attached at the bottom to the floor through the wall bottom plate. The walls are attached at the top to the next-level floor framing or in a one-story building to the roof framing. Figure 9-23 is an example of platform framing in a two-story building. This method is commonly used on all types of foundation;systems, including walls, piles, piers, and columns consisting of wood, masonry, and concrete materials. Less common framing methods in wood-frame construction are balloon framing in which wall studs are continuous from the foundation to the roof and post-and-beam framing in which a structure of beams and columns is constructed first, including the floors and roof, and then walls are built inside the beam and column structure. 9.2.5.2 Concrete/Masonry Masonry exterior walls are normally constructed to full height / f" _ (similar to wood balloon framing), and then wood floors � NOTE and the roof are framed into the masonry. Fully or partially reinforced and grouted masonry is required in high-wind and Masonry frames typically require seismic hazard areas. Floor framing is normally supported by continuous footings. However, a ledger board fastened to a bond beam in the masonry, and continuous footings are not the roof is anchored to a bond beam at the top of the wall. allowed in Zone V or Coastal A Connections can be via a top plate as shown in Figure 9-24 or Zones and are not recommended in Zone A. direct embedded truss anchors in the bond beam as shown in COASTAL CONSTRUCTION MANUAL 9-27 1 9 DESIGNING THE BUILDING Volume II Figure 9-23. ii Example of two-story platform framing on a �� 00: 0 pile-and-beam foundation Eiiimmi =a Double top plate Bottom plate Subfloor ►ca Double top plate ►_ �a Bottom plate Subfloor e Band board `1 Beam ►e11°I°I I J Pile Figure 9-6. Options for end walls are hip roofs,continuous masonry gables,and braced gable frames. Details and design tables for all of the above can be found in ICC 600-2008. Figure 9-24 is an example of masonry wall construction in a two-story building. 9.2.5.3 Moment-Resisting Frames Over the past few decades, an increasing number of moment-resisting frames have been built and installed in coastal homes (Hamilton 1997).The need for this special design is a result of more buildings in coastal high hazard areas being constructed with large glazed areas on exterior walls, with large open interior areas, and with heights of two to three stories. Figure 9-25 shows a typical steel moment frame. Large glazed areas pose challenges to the designer because they create: c Large openings in shear walls L: Large deflection in shear walls r Difficulties in distributing the shear load to the foundation 9-28 COASTAL CONSTRUCTION MANUAL 9 Volume II DESIGNING THE BUILDING 9 'I Rafter Figure 9-24. Two-story masonry wall Top plate' with wood floor and roof orframing LI Ceiling joist Bond beam Wood floor joists Subfloor Bond beam IM p; Ledger board Masonry wall Concrete slab Continuous footing Figure 9-25. Steel moment frame with i ii -riquitilmirikI large opening ! 1 illair„I I I j :� n ,,` t` f y i ' 1 kijil 1111111 IIII (01111 r , I rw `` { t r-i k .4. , ,2, -,. .,.,_.... p_. UdL ' , 'tee r�� 1U PO ..... III 0 Y A' I . „ 1- . 1 ' 11111. NS ;4 ' I .. .ram'• y R aft''•>�': ,_ •. 4 LI - . 4 , COASTAL CONSTRUCTION MANUAL 9-29 ,1 1 9 DESIGNING THE BUILDING Volume II L A moment-resisting frame usually resists shear Ely taking the lateral load into the top of the frame thus creating a moment at the base of the frame. The design professional must design a moment connection at the base between the steel frame and the wood, masonry, or concrete foundation. In residential construction, moment frames are frequently tubular steel. Tubular steel shapes that are close to the size of nominal framing lumber can be selected. This approach alleviates the need for special, time- consuming methods required to make the steel frame compatible with wood; however, frames made with tubular steel are more difficult to build than frames made with "H" or "WF" flange shapes because all connections in the frame are welded.There are a number of pre-manufactured moment frame products on the market now that have been designed for a variety of lateral forces to fit a variety of wall lengths and heights. 9.2.6 Roof Shape Roof shape, both the structural aspect and the covering, plays a significant role in roof performance. Compared to other types of roofs, hip roofs generally perform better in high winds because they have fewer sharp corners and fewer distinctive building geometry changes. Steeply pitched roofs usually perform better than flat roofs. Figures 9-26 and 9-27 show two types of roofs in areas of approximately similar terrain that experienced the winds of Hurricane Marilyn. The gable roof in Figure 9-26 failed, while the hip roof in Figure 9-27 survived the same storm with little to no damage. Whether the roof is a gabled roof or hip roof, proper design and construction are necessary for successful performance in high-wind events. 9.3 Breakaway Wall Enclosures In Zone V and Coastal A Zones, breaking waves,are almost certain to occur simultaneously with peak flood conditions. As breaking waves pass an open piling or column foundation, the foundation experiences cyclic fluid impact and drag forces. The flow peaks at the wave crest, just as the wave breaks. Although the flow creates drag on the foundation, most of the flow under the building is undisturbed. This makes open foundations somewhat resistant to wave actions and pile and column foundations a manageable design. When a breaking wave hits a solid wall, the effect is quite different.When the crest of a breaking wave strikes a vertical surface, a pocket of air is trapped and compressed by the wave. As the air pocket compresses, it exerts a high-pressure burst on the vertical surface, focused at the stillwater level. The pressures can be extreme. For example, a 5-foot wave height can produce a peak force of 4,500 pounds/square foot, roughly 100 times the force caused by a 170-mph wind.These extremely high loads make designing solid foundation walls for small buildings impractical in areas subject;to the effects of breaking waves. Prudent design dictates elevating buildings on an open foundation above potential breaking waves. In fact, the 2012 IBC and the 2012 IRC require that new, substantially damaged, and substantially improved buildings in Zone V be elevated above the BFE on an open foundation (e.g.,, pile, post, column, pier). The 2012 IBC and 2012 IRC prohibit obstructions below elevated buildings but allow enclosures below the BFE as long as they are constructed with insect screening, lattice, or walls designed and constructed to fail under the loads imposed by floodwaters (termed "breakaway walls"). Because such enclosures fail under flood forces, they do not transfer additional significant loads to the foundation. Regulatory requirements and design criteria concerning enclosures and breakaway walls below elevated buildings in Zone V are discussed in FEMA NFIP Technical Bulletin 9 (FEMA 2008a). Additional guidance is contained in Fact 9-30 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9 ,r Figure 9-26. Gable-end failure caused ___________________________________________________ by high winds, Hurricane Marilyn (U.S.Virgin Islands, 1995) - - 1 niir..1.„4.:41- 2,,,,..' f.. --*,_..,* ;.:1-.."' .q4.:"---",':2 I ‘ - "I . ' 117 11 Gyr I r Figure 9-27. Hip roof that survived high winds with little to no damage, Hurricane -'';4 Marilyn (U.S.Virgin .'A 9 " +.. ..--__ Islands, 1995) / 4- f x^^ • 1 ` f� 1 a • , , jimasitaig ,I --.:.. ..- I, ;r �; � ��61III��"tl,��l�lll ll 11 _, ___''- ----.---, ..- irrf-fAn; 43. r. F , COASTAL CONSTRUCTION MANUAL 9-31 r 9 DESIGNING THE BUILDING Volume II Sheet No. 8.1,Enclosures and Breakaway Walls in F.EMA P-499. Breakaway walls may be of wood-or metal- frame or masonry construction. Figure 9-28 shows how a failure begins in a wood-frame breakaway wall. Note the failure of the connection between the bottom plate of the wall and the floor of the enclosed area. Figure 9-29 shows a situation in which utility components placed on and through a breakaway wall prevented it from breaking away cleanly. To increase the likelihood of collapse as intended, it is recommended that the vertical framing members (such as 2x4s) on which the screen or lattice work is mounted be spaced at least 2 feet apart. Either metal or synthetic screening is acceptable. Wood and plastic lattice is available in 4-foot x 8-foot sheets. The material used to fabricate the lattice should be no thicker than 1/2 inch,and the finished sheet should have an opening ratio of at least 40 percent. Figure 9-30 shows lattice used to enclose an area below an elevated building. Figure 9-28. f r ° - Typical failure mode of —fir breakaway wall beneath -- _ - ' i _ _- an elevated building— � `� • F`-- __"� failure of the connection '.,�\ •-. , _ -—r�_ between the bottom plate •, y; .•:.: . - •., y l•.. of the wall and the floor r0 ! : : - of the enclosed area, Abu Hurricane Hugo(South ~,,p. ( I� Carolina, 1989) �i" , 1 I .� r' _ -' I :3 : ;,, ,,,--0;c7", , , _------ 6. ,' .,I, - , *9 .C' • --' ' ' - yam, Figure 9-29. - - ' ' . " Breakaway wall panel r ``,'k , _I • �4�`� prevented from breaking a away cleanly by utility " 1_ penetrations, Hurricanedi _ - Opal (Florida, 1995) I . 'i 1. t �� ;I(1 -i 1 [ ' ' • • 1' t r-:--,:,,_ . ', , _. -, ‘ ; , ,\4 ( i Ili)16; - _,_------- 13.E . j 9-32 COASTAL CONSTRUCTION MANUAL i 1 Volume II DESIGNING THE BUILDING 9 Figure 9-30. - � Lattice beneath an = elevated house in Zone V a Ct:(lj T ' .1 Will �.�7,� C • is � r-i{ }=e•�=.' 1 cr17p `,/ �.�. � i . .I �ldi, 1 llP.' ' 461 4,11• f1-°it . _w+•. .I' i 1 9 R C �y" 5, V I I + I I 11 • • %b `(iii t r• N1 • ' I _ t�y f 4 • I • • `s• •it • 9.4 Building Materials The choice of materials is influenced by many considerations, including whether the materials will be used above or below the DFE. Below the DFE, design considerations include the risk of inundation by seawater, and the forces to be considered include those from wave action,water velocity,and waterborne debris impact. Materials intermittently wetted by floodwater below the BFE are subject to corrosion and decay. Above the DFE, building materials also face significant environmental effects. The average wind velocity increases with height above ground.Wind-driven saltwater spray can cause corrosion and moisture intrusion. 'The evaporation of saltwater leaves crystalline salt that retains water and is corrosive. Each type of commonly used material (wood, concrete, steel, and masonry) has both characteristics that can be advantageous and that can require special consideration when the materials are used in the coastal environment (see Table 9-1).A coastal residential structure usually has a combination of these materials. Table 9-1. General Guidance for Selection of Materials Material Advantages Special Considerations • Generally available and commonly used • Easily over-cut, over-notched, and over-nailed •With proper design, can generally be used • Requires special treatment and continued Wood in most structural application's maintenance to resist decay and damage •Variety of products available from termites and marine borers •Can be treated to resist decay • Requires protection to resist weathering •Some species are naturally decay-resistant • Subject to warping and deterioration • Used for forces that are larger than wood • Not corrosion-resistant can resist • Heavy and not easily handled and fabricated Steel • Can span long distances by carpenters • Can be coated to resist corrosion • May require special connections such as welding COASTAL CONSTRUCTION MANUAL 9-33 9 DESIGNING THE BUILDING Volume II Table 9-1. General Guidance for Selection of Materials1(concluded) Material Advantages Special Considerations • Resistant to corrosion if reinforcing is •Saltwater infiltration into concrete cracks properly protected causes reinforcing steel corrosion Reinforced • Good material for compressive loads • Pre-stressed members require special Concrete • Can be formed into a variety of shapes handling • Pre-stressed members have high load •Water intrusion and freeze-thaw cause capacity deterioration and spalling • Resistant to corrosion if reinforcing is • Not good for beams and girders properly protected •Water infiltration into cracks causes Masonry reinforcing steel corrosion • Good material for compressive loads • Requires reinforcement to resist loads in • Commonly used in residential construction coastal areas 9.4.1 Materials Below the DFE The use of flood-resistant materials below the BFE is discussed NOTE in FEMA NFIP Technical Bulletin 2 (FEMA 2008b). According to the bulletin, "All construction below the lowest Although NFIP regulations, 2012 floor is susceptible to flooding and must consist of flood- IBC, and 2012 IRC specify that resistant materials. Uses of enclosed areas below the lowest ' flood-resistant materials be used floor in a residential building are limited to parking, access, below the BFE, in this Manual, flood-resistant materials below and limited storage—areas that can withstand inundation by the DFE are recommended. floodwater without sustaining significant structural damage." The 2012 IBC and 2012 IRC require that all new construction and substantial improvements in the SFHA be constructed with materials that are resistant to flood damage. Compliance with these requirements in coastal areas means that the only building elements below the BFE are: L. Foundations—treated wood; concrete or steel piles; concrete or masonry piers; or concrete, masonry, or treated CROSS REFERENCE wood walls For NFIP compliance provisions rBreakaway walls as described in the 2012 IBC and the 2012 IRC,see Chapter 5 of -" Enclosures used for parking, building access, or storage this Manual. i- below elevated buildings r Garages in enclosures under elevated buildings or attached to buildings CROSS REFERENCE �- Access stairs - For examples of flood insurance Material choices for these elements are limited to materials that premiums for buildings in which meet the requirements provided in FEMA NFIP Technical the lowest floor is above the BFE and in which there is an enclosure Bulletin 2. Even for materials meeting those requirements, below the BFE, see Table 7-2 in characteristics of various materials can be advantageous or may Chapter 7. require special consideration when the materials are used for 9-34 COASTAL CONSTRUCTION MANUAL Volume II + DESIGNING THE BUILDING 9 different building elements.Additional information about material selection for various locations and uses in a building is included in"Material Durability'in Coastal Environments,"available on the Residential Coastal Construction Web site (http://www.fema.gov/rebuild/mat/fema55.shtm). 9.4.2 Materials Above the DFE Long-term durability, architectural, and structural considerations are normally the most important factors in material selection. Material that will be used in a coastal environment will be subjected to weathering, corrosion, termite damage, and decay from water infiltration, in addition to the stresses induced by loads from natural hazard events.These influences are among the considerations for selecting appropriate materials. "Material Durability in Coastal Environments" contains additional information about a variety of wood products and the considerations that are important in their selection and use. 9.4.3 Material Combinations Materials are frequently combined in the construction of a single residence.The most common combinations are as follows: Masonry or concrete lower structure with wood on upper level Wood piles supporting concrete pile caps and columns that support a wood superstructure Steel framing with wood sheathing For the design professional working with of coastal buildings, important design considerations when combining materials include: 1. The compatibility of metals is a design consideration because dissimilar metals that are in contact with each other may corrode in the presence of salt and moisture. "Material Durability in Coastal Environments" addresses a possible problem when galvanized fasteners and hardware are in contact with certain types of treated wood. 2. Connecting the materials together is crucial. Proper embedment of connectors (if into concrete or masonry) and proper placement of connectors are necessary for continuity of the vertical or horizontal load path.Altering a connector location after it has been cast into concrete or grout is a difficult and expensive task. 3. Combining different types of material in the same building adds to construction complexity and necessitates additional skills to construct the project. Figure 9-31 shows a coastal house being constructed with preservative-treated wood piles that support a welded steel frame, resulting in metal coming into direct contact with treated wood. 4. Material properties, such as stiffness of one material relative to another, affect movement or deflection of one material relative to the other. COASTAL CONSTRUCTION MANUAL 9-35 9 DESIGNING THE BUILDING Volume II Figure 9-31. r , House being constructed 6 ,• b - with a steel frame on -* 0" wood piles P/ - 1 1.. ete.. 4' At • in tf, • 9.4.4 Fire Safety Considerations Designing and constructing townhouses and low-rise multi-family coastal buildings to withstand natural hazards and meet the building code requirements for adequate fire separation presents some challenges. Although fire separation provisions of the 2012 IBC and 2012 IRC differ, they both require that the common walls between living units be constructed of materials that provide a minimum fire resistance rating. The intent is for units to be constructed so that if a fire occurs in one unit, the structural frame of that unit would collapse within itself and not affect either the structure or the fire resistance of adjacent units. For townhouse-like units, the common framing method is to use the front and rear walls for the exterior load-bearing walls so that firewalls can be placed between the units. Beams that are parallel to the front and rear exterior walls are typically used to provide support for these walls as well as the floor framing. Figure 9-32 illustrates a framing system for a series of townhouses in which floor beams are perpendicular to the primary direction of flood forces. Design issues include the following: 5. The floor support beams are parallel to the shore and perpendicular to the expected flow and may therefore create an obstruction during a greater-than-design flood event. 6. The fire separation between townhouse units limits options for structural connections between units, making the transfer of lateral loads to the foundation more difficult to achieve. 7. The exposed undersides of buildings elevated on an open foundation (e.g., pile, pier, post, column) must be protected with a fire-rated material. Typically, this is accomplished with use of fire-resistant gypsum board; however, gypsum board is not a flood-damage-resistant material. An alternative approach is to use other materials such as cement-fiber board (with appropriate fire rating), which has a greater resistance to damage from floodwaters, and fire retardant treated wood. Other alternative materials or methods of protection that are flood-damage-resistant may be required in order to meet the competing demands of flood- and fire-resistance. 9-36 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9 Figure 9-32. Primary direction of flood forces Townhouse framing Shoreline system Floor beams If parallel to` - Pile-supported shore buildings Floor joist _ Pile direction Separation required Plan view by fire code provisions of townhouse foundation 8. The requirement for separation of the foundation elements between townhouse units makes structural rigidity in the direction parallel to the shore more difficult to achieve. If the houses in Figure 9-32 were in a seismic hazard area, the designer could decide to place diagonal bracing parallel to the shore (i.e., perpendicular to the primary flood flow direction) or use more closely spaced and larger piles. Diagonal bracing would provide rigidity but would also create an obstruction below the DFE. The design professional should consult FEMA NFIP Technical Bulletin 5 (FEMA 2008c) for information about the types of construction that constitute an obstruction. One solution to some of the issues illustrated by Figure 9-32 would be to use two parallel independent walls to provide the required fire separation between units. Each wall could be attached to the framing system of the unit on one side of the separation and supported by a beam running perpendicular to the shore and bearing on the open foundation of that unit. 9.4.5 Corrosion Modern construction techniques often rely heavily on metal .-1 CROSS REFERENCE fasteners and connectors to resist the forces of various coastal hazards. To be successful, these products must have lifetimes For additional information about that are comparable to those of the other materials used for corrosion of metal connectors in coastal construction, see FEMA construction. Near saltwater coastlines, corrosion has been NFIP Technical Bulletin 8-96. found to drastically shorten the lifetime of standard fasteners _ and connectors. Corrosion is one of the most underestimated hazards affecting the overall strength and lifetime of coastal buildings. To be successful, hazard-resistant buildings must match the corrosion exposure of each element with the proper corrosion-resistant material. COASTAL CONSTRUCTION MANUAL 9-37 9 DESIGNING THE BUILDING Volume II 9.5 Appurtenances CROSS REFERENCE The NFIP regulations define "appurtenant structure" as "a =_ structure which is on the same parcel of property as the principal For additional information about structure to be insured and the use of which is incidental to the types of building elements that are allowed below the the use of the principal structure (44 CFR § 59.1). In this BFE and for respective site Manual, "appurtenant structure" means any other building development issues, see FEMA or constructed element on the same property as the primary NFIP Technical Bulletin 5. building, such as decks, covered porches, access to elevated _ buildings, pools, and hot tubs. 9.5.1 Decks and Covered Porches Attached to Buildings Many decks and other exterior attached structures have failed during hurricanes. For decks and other structures without roofs, the primary cause of failure has been inadequate support: the pilings have either not been embedded deep enough to prevent failure or have been too small to carry the large forces from natural hazards. The following are recommendations for designing decks and other exterior attached structures: r_. If a deck is structurally attached to a structure, the bottom of the lowest horizontal supporting member of the deck must be at or above the BFE. Deck supports that extend below the BFE (e.g., pilings, bracing) must comply with Zone V design and construction requirements. The structure must be designed to accommodate any increased loads resulting from the attached deck. Some attached decks are located above the BFE but rely on support elements that extend below the BFE. These supports must comply with Zone V design and construction requirements. r:: If a deck or patio (not counting its supports) lies in whole or in part below the BFE, it must be structurally independent from the structure and its foundation system. t: If the deck surface is constructed at floor level, the deck surface/floor level joint provides a point of entry for wind-driven rain. This problem can be eliminated by lowering the deck surface below the floor level. If deck dimensions can be accommodated with cantilevering from the building, this eliminates the need for piles altogether and should be considered when the deck dimensions can be accommodated with this structural technique. Caution must be exercised with this method to keep water out of the house framing. Chapter 11 discusses construction techniques for flashing cantilever decks that minimize water penetration into the WARNING house. Decks should not cantilever Exposure to the coastal environment is severe for decks over bulkheads retaining walls where waves can run up and other exterior appurtenant structures.Wood.must be the vertical wall and under the preservative-treated or naturally decay resistant, and fasteners deck. must be corrosion resistant. 9-38 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9 9.5.1.1 Handrails To minimize the effects of wind pressure, flood forces, and wave impacts, deck handrails should be open and have slender vertical or horizontal members spaced in accordance with the locally adopted building code. Many deck designs include solid panels (some made of impact-resistant glazing) between the top of the deck handrail and the deck. These solid panels must be able to resist the design wind and flood loads (below the DFE) or they will become debris. 9.5.1.2 Stairways Many coastal homes have stairways leading to ground level. During flooding, flood forces often move the stairs and frequently separate them from the point of attachment.When this occurs, the stairs become debris and can cause damage to nearby houses and other buildings. Recommendations for stairs that descend below the BFE include the following: E To the extent permitted by code, use open-riser stairs to let floodwater through the stair stringers and anchor the stringers to a permanent foundation by using, for example, piles driven to a depth sufficient to prevent failure from scour. D Extend the bottom of the stair carriages several feet below grade to account for possible scour. Stairs constructed in this fashion are more likely to remain in place during a coastal hazard event and therefore more likely to be usable for access after the event. In addition, by decreasing the likelihood of damage, this approach reduces the likelihood of the stairs becoming debris. 9.5.2 Access to Elevated Buildings The first floor of buildings in the SFHA is elevated from a few feet to many feet above the exterior grade in order to protect the building and its contents from flood damage. Buildings in Zone A may be only a few feet above grade; buildings in Zone V may be 8 feet to more than 12 feet above grade. Access to these elevated buildings must be provided by one or more of the following: O Stairs 0 Ramps 13 Elevator Stairs must be constructed in accordance with the local building code so that the run and rise of the stairs conform to the requirements.The 2012 IBC and 2012 IRC require a minimum run of 11 inches per stair tread and a maximum rise of 7 inches per tread.An 8-foot elevation difference requires 11 treads or almost 12 feet of horizontal space for the stairs. Local codes also have requirements concerning other stair characteristics, such as stair width and handrail height. Ramps that comply with regulations for access by persons with disabilities must have a maximum slope of 1:12 with a maximum rise of 30 inches and a maximum run of 30 feet without a level landing. The landing length must be a minimum of 60 inches. As,a result, access ramps are generally not practical for buildings elevated more than a few feet above grade and then only when adequate space is available. COASTAL CONSTRUCTION MANUAL 9-39 9 DESIGNING THE BUILDING Volume II Elevators are being installed in many one- to I four-family - residential structures and provide an easy way to gain access CROSS REFERENCE to elevated floors of a building (including the first floor). There - must be an elevator entrance on the lowest floor; therefore, in For more information about elevator installation in buildings flood hazard areas, some of the elevator equipment may be located in SFHAs, see FEMA below the BFE. FEMA's NFIP Technical Bulletin 4 (FEMA NFIP Technical Bulletin 4. 2010a) provides guidance on how to install elevators so that damage to elevator elements is minimized during a flood. 9.5.3 Pools and Hot Tubs Many homes at or near the coast have a swimming pool or hot tub as an accessory. Some of the pools are fiberglass and are installed on a pile-supported structural frame. Others are in-ground concrete pools. The design professional should consider the following when a pool is to be installed at a coastal home: tl Only an in-ground pool may be constructed beneath an elevated Zone V building. In addition, -- -. the top of the pool and the accompanying deck NOTE or walkway must be flush with the existing grade, and the area below the lowest floor of the building Check with local floodplain management must remain unenclosed. officials for information about regulations governing the disturbance of primary Enclosures around pools beneath elevated frontal dunes. Such regulations can affect various types of coastal construction, buildings constitute recreational use and are including the installation of appurtenant therefore not allowed, even if constructed to structures such as swimming pools. breakaway standards. Lattice and insect screening are allowed because they do not create an enclosure under a community's NFIP-compliant floodplain management ordinance or law. NOTE 1- A pool adjacent to an elevated Zone V building The construction of pools below or may be either constructed at grade or elevated. adjacent to buildings in coastal high Elevated pools must be constructed on an open hazard areas must meet the requirements foundation and the bottom of the lowest horizontal presented in FEMA NFIP Technical structural member must be at or above the DFE so Bulletin 5. In general, pools must be that the pool will not act as an obstruction. (1) elevated above the BFE on an open foundation or(2) constructed in the ground in such a way as to minimize the The designer must assure community officials that effects of scour and the potential for the a pool beneath or adjacent to an elevated Zone creation of debris. V building will not be subject to breaking up or floating out of the ground during a coastal flood and will therefore not increase the potential for damage to the foundations and elevated portions of any nearby buildings. If an in-ground pool is constructed in an area that can be inundated by floodwaters, the elevation of the pool must account for the potential buoyancy of the pool. If a buoyancy check is necessary, it should be made with the pool empty. In addition, the design professional must design and site the pool so that any increased wave or debris impact forces will not affect any nearby buildings. 9-40 COASTAL CONSTRUCTION MANUAL 1 Volume II DESIGNING THE BUILDING 9 - Pools and hot tubs have water pumps, piping, heaters, filters, and other equipment that is expensive and that can be damaged by floodwaters and sediment.All such equipment should be placed above the DFE where practical. !- Equipment required for fueling the heater, such as electric meters or gas tanks, should be placed above the DFE. It may also be necessary to anchor the gas tank to prevent a buoyancy failure. r If buried, tanks must not be susceptible to erosion and scour and thus failure of the anchoring system. The design intent for concrete pools includes the following: Elevation of an in-ground pool should be such that scour will not permit the pool to fail from either normal internal loads of the filled pool or from exterior loads imposed by the flood forces. i The pool should be located as far landward as possible and should be oriented in such a way that flood forces are minimized. One way to minimize flood forces includes placing the pool with the narrowest dimension facing the direction of flow, orienting the pool so there is little to no angle of attack from floodwater, and installing a pool with rounded instead of square corners.All of these design choices reduce the amount of scour around the pool and improve the chances the pool will survive a storm. These concepts are illustrated in Figure 9-33. !- A concrete pool deck should be frangible so that flood forces create concrete fragments that help reduce scour. The concrete deck should be installed with no reinforcing and should have contraction joints placed at 4-foot squares to "encourage" failure. See Figure 9-34 for details on constructing a frangible concrete pad. E Pools should not be installed on fill in or near Zone V. Otherwise, a pool failure may result from scour of the fill material. For concrete pools, buoyancy failure is also possible when floodwaters cover the pool. In addition,flood flows can scour the soil surrounding a buried pool and tear the pool from its anchors. When this happens, the pieces of the pool become large waterborne debris. Figure 9-33. Frangible concrete deck Recommendations for House orientation of in-ground Rounded corners pools Narrowest dimension Porch 0°angle of attack lir Flood flow COASTAL CONSTRUCTION MANUAL ,i 9-41 9 DESIGNING THE BUILDING i Volume II Figure 9-34. Recommended Contraction joint Isolation joint contraction joint layout Pile/column(typical) (typical—see detail) at pile/column for frangible slab-on- J 111 4 J L grade below elevated building Utility riser r, ❑ C ❑ 1 ❑ C —1 �n 11 El C Plan view Tooled contraction joint Tooled joint - :i., i :.ii • 4 inches maximum OgNMERMONAIWWWWWOMOI jr. - Crack resulting from concrete curing process Sawcut contraction joint ` - Sawcut joint 4 ,:::77WgVg!egftldag, !WAVAMMOWNSM Cyi, 4 inches maximum Jr Crack resulting from concrete curing process Detail—section through slab Note: Install expansion and isolation joints as appropriate in accordance with standard practice or as required by state and local codes. 9-42 COASTAL CONSTRUCTION MANUAL 1 Volume II DESIGNING THE BUILDING 9 9.6 References AF&PA (American Forest &Paper Association). 2008. Special Design Provisions for Wind and Seismic. ANSI/AF&PA SDPWS-08. AF&PA. 2012. Wood Frame Construction Manual for One-and Two-Family Dwellings. Washington, DC. ASCE (American Society of Civil Engineers). 2010.Minimum Design Loads for Buildings and Other Structures, ASCE Standard ASCE 7-10. AWC (American Wood Council). 2001. Wood Frame Construction Manual. AWC. 2006. National Design Specification for Wood Construction (NDS). FEMA(Federal Emergency Management Agency). 1996. Corrosion Protection of Metal Connectors in Coastal Areas for Structures Located in Special Flood Hazard Areas. NFIP Technical Bulletin 8-96. FEMA. 2008a. Design and Construction Guidance for Breakaway Walls Below Elevated Coastal Buildings, FEMA NFIP Technical Bulletin 9. FEMA. 2008b. Flood Damage-Resistant Materials Requirements, FEMA NFIP Technical Bulletin 2. FEMA. 2008c. Free of Obstruction Requirements for Buildings Located in Coastal High Hazard Areas. NFIP Technical Bulletin 5. FEMA. 2009. Local Officials Guide for Coastal Construction. FEMA 762. FEMA. 2010a. Elevator Installation for Buildings Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program. NFIP Technical Bulletin 4. FEMA. 2010b. Home Builder's Guide to Coastal Construction Technical Fact Sheets. FEMA P-499. Hamilton, P. 1997. "Installing a Steel Moment Frame."Journal of Light Construction. March. ICC (International Code Council). 2008. Standard for Residential Construction in High-Wind Regions. ICC 600-2008. ICC: Country Club Hills, IL. ICC. 2011a. International Building Code. 2012 IBC. ICC: Country Club Hills, IL. ICC. 2011b. International Residential Code for One-and Two-Family Dwellings. 2012 IRC. ICC: Country Club Hills, IL. WPPC (Wood Products Promotion Council). 1996. Guide to Wood Construction in High Wind Areas. COASTAL CONSTRUCTION MANUAL 9-43 COASTAL CONSTRUCTION MANUAL r ; rVEA f:Ii) Icr•Y ; sue ••„ *6t re =,.„f .i I,• 't ' ■Designingthe Foundation ,_ This chapter provides guidance on designing foundations, - including selecting appropriate materials, in coastal areas. It CROSS REFERENCE provides general guidance on designing foundations in a coastal - environment and is not intended to provide complete guidance For resources that augment the on designing foundations in every coastal area. Design guidance and other information in this Manual, see the Residential professionals should consult other guidance documents, codes, Coastal Construction Web site and standards as needed. (http://www.fema.gov/rebuild/ mat/fema55.shtm). Design considerations for foundations in coastal environments , are in many ways similar to those in inland areas. Like all foundations, coastal foundations must support gravity loads, resist uplift and lateral loads, and maintain lateral and vertical load path continuity from the elevated building to the soils below. Foundations in coastal areas are different in that they must generally resist higher winds, function in a corrosive environment, and withstand the environmental aspects that are unique to coastal areas: storm surges, rapidly moving floodwaters, wave action, and scour and erosion. These aspects can make coastal flooding more damaging than inland flooding. Like many design processes,foundation design is an iterative process.First,the loads on the elevated structure are determined (see Chapter 9). Then a preliminary foundation design is considered, flood loads on the preliminary design are determined, and foundation style is chosen and the respective elements are sized to resist those loads. With information on foundation size, the design professional can accurately determine flood loads on the foundation and can, through iteration, develop an efficient final design. Because flood loads depend greatly on the foundation design criteria, the discussion of foundation design begins there. The appropriate styles of foundation are then discussed and how the styles can be selected to reduce vulnerability to natural hazards. COASTAL CONSTRUCTION MANUAL 10-1 i 10 DESIGNING THE FOUNDATION Volume II The distinction between code requirements and best:practices is described throughout the chapter. 10.1 Foundation Design Criteria Foundations should be designed in accordance with the latest edition of the 2012 IBC or the 2012 IRC and must address any locally adopted building ordinances. Designers will find that other resources will likely be needed in addition to the building codes in order to properly design a coastal foundation.These resources are listed at the end of this chapter. Properly designed and constructed foundations are expected to: r] Support the elevated building and resist all loads expected to be imposed on the building and its foundation during a design flood, wind, or seismic event £ In SFHAs, prevent flotation, collapse, and lateral movement of the building Function after being exposed to scour and erosion In addition, the foundation must be constructed with flood-resistant materials below the BFE. See Technical Bulletin 2, Flood Damage-Resistant Materials Requirements (FEMA 2008a), and Fact Sheet 1.7, Coastal Building Materials, in FEMA P-499 (FEMA 2011). Some coastal areas mapped as Zone A are referred to as "Coastal A Zones." Following Hurricane Katrina (2005), Coastal A Zones C4))/- TERMINOLOGY: have also been referred to as areas with a Limit of Moderate LiMWA AND Wave Action (LiMWA). Buildings in Coastal A Zones may be COASTAL A ZONE subjected to damaging waves and erosion and, when constructed Limit of Moderate Wave Action to minimum NFIP requirements for Zone A, may sustain major (LiMWA) is an advisory line damage or be destroyed during the base flood. Therefore, in this indicating the limit of the 1.5- Manual,foundations for buildings in Coastal A Zones are strongly foot wave height during the base flood. FEMA requires new recommended to be designed and constructed with foundations flood studies in coastal areas that resist the damaging effects of waves. to delineate the LiMWA. 10.2 Foundation Styles In this Manual, foundations are described as open or closed and shallow or deep. The open and closed descriptions refer to the above-grade portion of the foundation. The shallow and deep descriptions refer to the below-grade portion. Foundations can be open and deep, open and shallow, or closed and shallow. Foundations can also be closed and deep, but these foundations are relatively rare and generally found only in areas where (1) soils near the surface are relatively weak (700 pounds/square foot bearing capacity or less), (2) soils near the surface contain expansive clays (also called shrink/swell soils) that shrink when dry and swell when wet, or (3) other soil conditions exist that necessitate foundations that extend into deep soil strata to provide sufficient strength to resist gravity and lateral loads. Open, closed, deep, and shallow foundations are described in the following subsections. 10-2 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 1 0 10.2.1 Open Foundations An open foundation allows water to pass through the foundation of an elevated building,reducing the lateral flood loads the foundation must resist.Examples of open foundations are pile,pier, and column foundations. An open foundation is designed and constructed to minimize the amount of vertical surface area that is exposed to damaging flood forces. Open foundations have the added benefit of being less susceptible than closed foundations to damage from flood-borne debris because debris is less likely to be trapped. Open foundations are required in Zone V and recommended in Coastal A Zone. Table 10-1 shows the recommended practices in Coastal A Zone and Zone V. Table 10-1. Foundation Styles in Coastal Areas Foundation Style Zone V Coastal A Zone (LiMWA) Zone A Open/deep Acceptable Acceptable Acceptable Open/shallow Not permitted Acceptable(a) • • Acceptable Closed/shallow Not permitted Not recommended Acceptable Closed/deep � Not permitted Not recommended Acceptable LiMWA=Limit of Moderate Wave Action (a) Shallow foundations in Coastal A Zone are acceptable only if the maximum predicted depth of scour and erosion can be accurately predicted and foundations can be constructed to extend below that depth. 10.2.2 Closed Foundations A closed foundation is typically constructed using continuous perimeter foundation walls. Examples of closed foundations are crawlspace foundations and stem wall foundations,' which are usually filled with compacted soil. Slab-on-grade foundations are also considered closed. A closed foundation does not allow water to pass easily through the foundation elements below an elevated building. Thus, these types of foundations obstruct floodwater flows and present a large surface area upon which waves and flood forces act. Closed foundations are prohibited in Zone V and are not recommended in Coastal A Zones. If perimeter walls enclose space below the DFE, they must be equipped with openings that allow floodwaters to flow in and out of the area enclosed by the walls (see Figure 2-19). The entry and exit of floodwater equalizes the water pressure on both sides of the wall and reduces the likelihood that the wall will fail. See Fact Sheet No. 3.5,Foundation Walls, in FEMA P-499,Home Builder's Guide to Coastal Construction Technical Fact Sheet Series (FEMA 2010). Closed foundations also create much larger obstructions to moving floodwaters than open foundations, which significantly increases localized scour. Scour, with and without generalized erosion, can remove soils that support a building and can undermine the foundation and its footings. Once undermined, shallow footings readily fail (see Figure 10-1). 1 Stem wall foundations(in some areas,referred to as chain wall foundations)are similar to crawlspace foundations where the area enclosed by the perimeter walls are filled with compacted soil.Most stem wall foundations use a concrete slab-on-grade for the first floor.The NFIP requires flood vents in crawlspace foundations but not in stem wall foundations(see Section 6.1.1.1 and Section 7.6.1.1.5). COASTAL CONSTRUCTION MANUAL 10-3 1 0 DESIGNING THE FOUNDATION Volume II -r ., -' a y i. iro,t1 0 1 . -0.441 LE11111mom.,..._LAIL-- i Figure 10-1. Closed foundation failure due to erosion and scour undermining; photograph on right shows a close-up view of the foundation failure and damaged house wall, Hurricane Dennis (Navarre Beach, FL, 2005) 10.2.3 Deep Foundations Buildings constructed on deep foundations are supported by soils that are not near grade. Deep foundations include driven timber, concrete or steel piles, and caissons. Deep foundations are much more resistant to the effects of localized scour and generalized erosion than shallow foundations. Because of that, deep foundations are required in Zone V where scour and erosion effects can be extreme. Open/deep foundations are recommended in Coastal A Zones and in some riverine areas where scour and erosion can undermine foundations. 10.2.4 Shallow Foundations Buildings constructed on shallow foundations are supported by soils that are relatively close to the ground surface. Shallow foundations include perimeter strip footings, monolithic slabs, discrete pad footings, and some mat foundations. Because of their proximity to grade, shallow foundations are vulnerable to damage from scour and erosion, and because of that, they are not allowed in Zone V and are not recommended in Coastal A Zones unless they extend below the maximum predicted scour and erosion depth. In colder regions, foundations are typically designed to extend below the frost depth, which can exceed several feet below grade. Extending the foundation below the frost depth is done to prevent the foundation from heaving when water in the soils freeze and to provide adequate protection from scour and erosion. However,scour and erosion depths still need to be investigated to ensure that the foundation is not vulnerable to undermining. 10.3 Foundation Design Requirements and Recommendations Foundations in coastal areas must elevate the home to satisfy NFIP criteria. NFIP criteria vary for Zone V and Zone A. In Zone V, the NFIP requires that the building be elevated so that the bottom of the lowest 10-4 COASTAL CONSTRUCTION MANUAL Volume II i DESIGNING THE FOUNDATION 10 horizontal structural member is elevated to l the BFE. In Zone A, the NFIP requires that the home be constructed such that the top of the lowest Nor is elevated to the BFE. In addition to elevation, the NFIP contains other requirements regarding foundations. Because of the increased flood, wave, flood-borne debris, and erosion hazards in Zone V, the NFIP requires homes to be elevated on open/deep foundations that are designed to withstand flood forces, wind forces, and forces for flood-borne debris impact. They must also resist scour and erosion. 10.3.1 Foundation Style Selection Many foundation designs can be used to elevate buildings to the DFE. Table 10-1 shows which foundation styles are acceptable,not recommended,or not permitted in Zone V,Coastal A Zone,and Zone A.Additional information concerning foundation performance can be found in Fact Sheet 3.1, Foundations in Coastal Areas, in FEMA P-499. A best practices approach in the design and construction of coastal foundations is warranted because of the extreme environmental conditions in coastal areas, the vulnerability of shallow foundations to scour and erosion, the fact that the flood loads on open foundations are much lower than those on closed foundations, and foundation failures typically result in extensive damage to or total destruction of the elevated building. Structural fill can also be used to elevate and support stem wall,crawlspace,solid wall,slab-on-grade,pier,and column foundations in areas not subject to damaging wave action,erosion,and scour.The NFIP precludes the use of structural fill in Zone V. For more information, see FEMA Technical Bulletin 5, Free-of-Obstruction Requirements(FEMA 2008b). 10.3.2 Site Considerations The selected foundation design should be based on the characteristics of the building site.A site characteristic study should include the following: o Design flood conditions. Determine which flood zone the site is located in—Zone V, Coastal A Zone, or Zone A. Flood zones have different hazards and design and construction requirements. • Site elevation. The site elevation and DFE determine how far the foundation needs to extend above grade. E Long-and short-term erosion. Erosion patterns (along with scour) dictate whether a deep foundation is required. Erosion depth affects not only foundation design but also flood loads by virtue of its effect on design stillwater depth (see Section 8.5). o Site soils. A soils investigation report determines the soils that exist on the site and whether certain styles of foundations are acceptable. 10.3.3 Soils Data Accurate soils data are extremely important in the design of flood-resistant foundations in coastal areas. Although many smaller or less complex commercial buildings and most homes in non-coastal areas are COASTAL CONSTRUCTION MANUAL 10-5 10 DESIGNING THE FOUNDATION Volume II designed without the benefit of specific soils data, all buildings in coastal sites, particularly those in Zone V, should have a thorough investigation of the soils at.the construction site. Soils data are available in numerous publications and from onsite soils tests. 10.3.3.1 Sources of Published Soils Data Numerous sources of soil information are available. Section 12.2 of the Timber Pile Design and Construction Manual(Collin 2002) lists the following: L Topographic maps from the U.S. Geologic Survey (USGS) 11 Topographic maps from the Army Map Service L: Topographic maps from the U.S. Coast and Geodetic Survey Topographic information from the USACE for some rivers and adjacent shores and for the Great Lakes and their connecting waterways Nautical and aeronautical charts from the Hydrographic Office of the Department of the Navy Geologic information from State and local governmental agencies, the Association of Engineering Geologists, the Geological Society of America, the Geo-Institute of the American Society of Civil Engineers, and local universities �= Soil survey maps from the Soil Conservation Service of the U.S. Department of Agriculture 10.3.3.2 Soils Data from Site Investigations Site investigations for soils include surface and subsurface investigations. Surface investigations can identify evidence of landslides,areas affected by erosion or scour,and accessibility for equipment needed for subsurface testing and for equipment needed in construction. Surface investigations can also help identify the suitability or unsuitability of particular foundation styles based on the past performance of existing structures. However, caution should be used when basing the selection of a foundation style solely on the performance of existing structures because the structures may not have experienced a design event. The 2012 IBC requires that geotechnical investigations be conducted by Registered Design Professionals.Section 1803.2 allows building officials to waive geotechnical investigations where satisfactory data are available from adjacent areas and demonstrate that investigations are not required.The 2012 IRC requires building officials to determine whether soils tests are needed where"quantifiable data created by accepted soil science methodologies indicate expansive, compressible, shifting or other questionable soil characteristics are likely to be present." Because of the hazards in coastal areas, a best practices approach is to follow the 2012 IBC requirements. Subsurface exploration provides invaluable data on soils at and below grade.The data are both qualitative(e.g., soil classification) and quantitative (e.g., bearing capacity). Although some aspects of subsurface exploration are discussed here, subsurface exploration is too complicated and site-dependent to be covered fully in one document. Consulting with geotechnical engineers familiar with the site is strongly recommended. 10-6 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 Subsurface exploration typically consists of boring or creating test pits, soils sampling, and laboratory tests. The Timber Pile Design and Construction Manual(Collin 2002) recommends a minimum of one boring per structure,a minimum of one boring for every 1,000 square feet of building footprint,and a minimum of two borings for structures that are more than 100 feet wide.Areas with varying soil structure and profile dictate more than the minimum number of borings.Again, local geotechnical engineers should be consulted. The following five types of data from subsurface exploration are discussed in the subsections below: soil classification, bearing capacity, compressive strength, angle of internal friction, and subgrade modulus. Soil Classification Soil classification qualifies the types of soils present along the boring depth.ASTM D2487-10 is a consensus standard for soil classification.Soil classification is based on whether soils are cohesive(silts and clays) or non- cohesive(composed of granular soils particles).The degree of cohesiveness affects foundation design. Coupled with other tests such as the plasticity/Atterburg Limits soil classification can identify unsuitable or potentially problematic soils.Table 10-2 contains the soil classifications from ASTM D2487-10.ASTM D2488-09a is a simplified standard for soil classification that may be used when directed by a design professional. Bearing Capacity Bearing capacity is a measure of the ability of soil to support gravity loads without soil failure or excessive settlement. Bearing capacity is generally measured in pounds/square foot and occasionally in tons/square foot. Soil bearing capacity typically ranges from 1,000 pounds/square foot (relatively weak soils) to more than 10,000 pounds/square foot (bedrock). Bearing capacity has a direct effect on the design of shallow foundations. Soils with lower bearing capacities require proportionately larger foundations to effectively distribute gravity loads to the supporting soils. For deep foundations,like piles,bearing capacity has less effect on the ability of the foundation to support gravity loads because most of the resistance to gravity loads is developed by shear forces along the pile. Presumptive allowable load bearing values of soils are provided in the 2012 IBC and the 2012 IRC.Frequently, designs are initially prepared based on presumed bearing capacities. The builder's responsibility is to verify that the actual site conditions agree with the presumed bearing capacities.As a best practices approach, the actual soil bearing capacity should be determined to allow the building design to properly account for soil capacities and characteristics. Compressive Strength Compressive strength is typically determined by Standard Penetration Tests. Compressive strength controls the design of shallow foundations via bearing capacity and deep foundations via the soil's resistance to lateral loads. Compressive strength is also considered when determining the capacity of piles to resist vertical loads. Compressive strength is determined by advancing a probe, 2 inches in diameter, into the bottom of the boring by dropping a 140-pound slide hammer a height of 30 inches. The number of drops, or blows, required to advance the probe 6 inches is recorded. Blow counts are then correlated to soil properties. COASTAL CONSTRUCTION MANUAL 10-7 I 10 DESIGNING THE FOUNDATION Volume II i Table 10-2.ASTM D2487-10 Soil Classifications � . o E Major Divisions cz cn Typical Names Classification Criteria Well-graded gravels Classification D60 - . : and gravel-sand on basis of Cu = mixtures, little or no i percentage of i Cio greater than 4 GW fines fines: rr z (D30/l • Less than 5% Cz = pass No.200 ! (Dio�(D6o) Clean gravels ! sieve: GW, between 1 and 3 Gravels: ,i GP, SW, SP •50° or Poorly graded Not meeting both criteria for GW more of . GP ! gravels and gravel- ; • More than sand mixtures, little 12/° pass coarse, ,y or no fines i No. 200 fraction __- sieve: GM, - retained Silty gravels,,gravel- GC, SM,SC Atterberg limits I Atterberg limits on No.4 . • sand-silt mixtures • 5%to 12% plot below plotting in sieve i GM pass No, A line or ; hatched area 200 sieve: plasticity index i are borderline Gravels ess than 4 ! classifications l with ;.._ _. - borderline l� _ -- -- j reirin fines Clayey gravels, classification Atterberg limits { seuof dual ,f gravel-sand-clay requiring dual plot above Coarse- GC mixtures symbols "A"line or symbols. grained . i I plasticity index soils more, . , I less than 7 than 50% _=-_.._-_ -_ --_-_- ------ -- .. — — — retained ; Well-graded sands D60 on No. . and gravelly sands, C. = 200 sieve ••I ' i little or no fines Cio greater than 6 SW • . Clean Cz = �D3o f sands lDio)lD60� 'i __ _ .._ _ ___ between 1 and 3 _ Sands: 1 Poorly graded sands i Not meeting both criteria for SW More° SP ; and gravelly sands, than 50/o little or no fines • of coarse -_____ =_ -__ _ - - --..--•- - - -- fraction , Silty sands, sand-silt ? Atterberg limits j Atterberg limits passes mixtures plot below plotting in No.4. SM ; "A"line or hatched area sieve . 1. I i plasticity index i are borderline : less than 4 ! classifications • with.e . i Clayey sands, sand- ; Atterberg requiring fines ! limits plot ; use of dual i clay mixtures .. � � symbols. SC above"A"line or plasticity { index greater j ' an , 10-8 COASTAL CONSTRUCTION MANUAL COASTAL CONSTRUCTION MANUAL }:y WSJ r,#� � - . - F v,A yin y • (` +e : Preface The 2011 Coastal Construction Manual, Fourth Edition (FEMA P-55), is a two-volume publication that provides a comprehensive approach to planning, siting, designing, constructing, and maintaining homes in the coastal environment. Volume I of the Coastal Construction Manual provides information about hazard identification, siting decisions, regulatory requirements, economic implications, and risk management. The primary audience for Volume I is design professionals, officials, and those involved in the decision-making process. Volume II contains in-depth descriptions of design, construction, and maintenance practices that, when followed, will increase the durability of residential buildings in the harsh coastal environment and reduce economic losses associated with costal natural disasters. The primary audience for Volume II is the design professional who is familiar with building codes and standards and has a basic understanding of engineering principles. Volume II is not a standalone reference for designing homes in the coastal environment.The designer should have access to and be familiar with the building codes and standards that are discussed in Volume II and listed in the reference section at the end of each chapter. The designer should also have access to the building codes and standards that have been adopted by the local jurisdiction if they differ from the standards and codes that are cited in Volume II. If the local jurisdiction having authority has not adopted a building code, the most recent code should be used. Engineering judgment is sometimes necessary, but designers should not make decisions that will result in a design that does not meet locally adopted building codes. The topics that are covered in Volume II are as follows: Chapter 7— Introduction to the design process, minimum design requirements, losses from natural hazards in coastal areas, cost and insurance implications of design and construction decisions, sustainable design, and inspections. COASTAL CONSTRUCTION MANUAL PREFACE Volume II Chapter 8— Site-specific loads, including from snow, flooding, tsunamis, high winds, tornadoes, seismic events, and combinations of loads. Example problems are provided to illustrate the application of design load provisions of ASCE 7-10,Minimum Design Loads for Buildings and Other Structures. D Chapter 9— Load paths, structural connections, structural failure modes, breakaway walls, building materials, and appurtenances. Chapter 10— Foundations, including design criteria, requirements and recommendations, style selection (e.g., open, closed), pile capacity in soil', and installation. E Chapter 11— Building envelope, including floors in elevated buildings, exterior doors, windows and skylights, non-loading-bearing walls, exterior wall coverings, soffits, roof systems, and attic vents. El Chapter 12— Installing mechanical equipment and utilities. L, Chapter 13— Construction, including the foundation, structural frame, and building envelope. Common construction mistakes, material selection and durability, and techniques for improving resistance to decay and corrosion are also discussed. Li Chapter 14— Maintenance of new and existing buildings, including preventing damage from corrosion, moisture, weathering, and termites; building elements that require frequent maintenance; and hazard-specific maintenance techniques. © Chapter 15— Evaluating existing buildings for'the need for and feasibility of retrofitting for wildfire, seismic, flood, and wind hazards and implementing the retrofitting. Wind retrofit packages that can be implemented during routine maintenance are also discussed (e.g., replacing roof shingles). For additional information on residential coastal construction, see the FEMA Residential Coastal Construction Web site at http://www.fema.gov/rebuild/mat/fema55.shtm. ii COASTAL CONSTRUCTION MANUAL COASTAL CONSTRUCTION MANUAL Fourth Edition Authors and Key Contributors William Coulbourne,Applied Technology Council Christopher P.Jones, Durham, NC Acknowledgments Omar Kapur, URS Group, Inc. Vasso Koumoudis, URS Group, Inc. Philip Line, URS Group, Inc. David K. Low, DK Low and Associates Glenn Overcash, URS Group, Inc. Samantha Passman, URS Group, Inc. Adam Reeder,Atkins Laura Seitz, URS Group, Inc. Thomas Smith,TLSmith Consulting Scott Tezak, URS Group, Inc.—Consultant Project Manager Fourth Edition Volume II Reviewers and Contributors Katy Goolsby-Brown, FEMA Region IV John Ingargiola, FEMA Headquarters—Technical Assistance and Research Contracts Program Manager John Plisich, FEMA Region IV Paul Tertell, FEMA Headquarters—Project Manager Ronald Wanhanen, FEMA Region VI Gregory P. Wilson, FEMA Headquarters Brad Douglas,American Forest and Paper Association Gary Ehrlich, National Association of Home Builders Dennis Graber, National Concrete Masonry Association David Kriebel, United States Naval Academy Marc Levitan, National Institute of Standards and Technology Tim Mays,The Military College of South Carolina Sam Nelson,Texas Department of Insurance Janice Olshesky, Olshesky Design Group, LLC Michael Powell, Delaware Department of Natural Resources and Environmental Control David Prevatt, University of Florida Timothy Reinhold, Insurance Institute for Business &Home Safety Tom Reynolds, URS Group, Inc. Michael Rimoldi, Federal Alliance for Safe Homes Randy Shackelford, Simpson Strong-Tie John Squerciati, Dewberry Keqi Zhang, Florida International University Fourth Edition Technical Editing, Layout, and Illustration Diana Burke, URS Group, Inc. Lee-Ann Lyons, URS Group, Inc. Susan Ide Patton, URS Group, Inc. Billy Ruppert, URS Group, Inc. COASTAL CONSTRUCTION MANUAL iii COASTAL CONSTRUCTION MANUAL Contents Chapter 7. Pre-Design Considerations 7-1 • 7.1 Design Process 7-2 7.2 Design Requirements 7-3 7.3 Determining the Natural Hazard Risk 7-3 7.4 Losses Due to Natural Hazards in Coastal Areas 7-5 7.5 Initial, Long-Term, and Operational costs 7-6 7.5.1 Cost Implications of Siting Decisions 7-7 7.5.2 Cost Implications of Design Decisions 7-7 7.5.3 Benefits and Cost Implications of Siting, Design, and Construction Decisions 7-11 7.6 Hazard Insurance 7-12 7.6.1 Flood Insurance 7-13 7.6.1.1 Rating Factors 7-13 7.6.1.2 Coverage 7-17 7.6.1.3 Premiums 7-18 7.6.1.4 Designing to Achieve Lower Flood Insurance Premiums 7-20 7.6.2 Wind Insurance 7-21 7.6.2.1 Territory 7-22 7.6.2.2 Fire Protection Class 7-22 7.6.2.3 Building Code Effectiveness Grading Schedule 7-22 7.6.2.4 Construction Type 7-23 7.6.2.5 Protective Devices 7-23 7.6.3 Earthquake Insurance 7-24 7.7 Sustainable Design Considerations 7-24 7.8 Inspection Considerations 7-25 7.9 References 7-26 COASTAL CONSTRUCTION MANUAL v CONTENTS Volume II Chapter 8. Determining Site-Specific Loads 1 8-1 8.1 Dead Loads 8-3 8.2 Live Loads 8-3 8.3 Concept of Tributary or Effective Area and Application of Loads to a Building 8-4 8.4 Snow Loads 8-5 8.5 Flood Loads 8-5 8.5.1 Design Flood 8-5 8.5.2 Design Flood Elevation 8-6 8.5.3 Design Stillwater Flood Depth 8-9 8.5.5 Design Breaking Wave Height 8-15 8.5.6 Design Flood Velocity 8-15 8.5.7 Hydrostatic Loads 8-17 8.5.8 Wave Loads 8-20 8.5.8.1 Breaking Wave Loads on Vertical Piles 8-21 8.5.8.2 Breaking Wave Loads on Vertical Walls 8-22 8.5.8.3 Wave Slam 8-25 8.5.9 Hydrodynamic Loads 8-28 8.5.10 Debris Impact Loads 8-31 8.5.11 Localized Scour 8-34 8.5.12 Flood Load Combinations 8-37 8.6 Tsunami Loads - 8-47 8.7 Wind Loads 8-47 8.7.1 Determining Wind Loads 8-49 8.7.2 Main Wind Force Resisting System 8-52 8.7.3 Components and Cladding 8-61 8.8 Tornado Loads 8-67 8.9 Seismic Loads 8-68 8.10 Load Combinations 8-73 8.11 References 8-81 vi COASTAL CONSTRUCTION MANUAL Volume II CONTENTS Chapter 9. Designing the Building 9-1 9.1 Continuous Load Path 9-1 9.1.1 Roof Sheathing to Framing Connection (Link#1) 9-4 9.1.2 Roof Framing to Exterior Wall (Link#2) 9-8 9.1.3 Wall Top Plate to Wall Studs (Link#3) 9-10 9.1.4 Wall Sheathing to Window Header (Link#4) 9-12 9.1.5 Window Header to Exterior Wall (Link#5) 9-12 9.1.6 Wall to Floor Framing (Link#6) 9-15 9.1.7 Floor Framing to Support Beam (Link#7) 9-17 9.1.8 Floor Support Beam to Foundation (Pile) (Link#8) 9-18 9.2 Other Load Path Considerations 9-21 9.2.1 Uplift Due to Shear Wall Overturning 9-21 9.2.2 Gable Wall Support 9-24 9.2.3 Connection Choices 9-24 9.2.4 Building Eccentricities 9-27 9.2.5 Framing System 9-27 9.2.5.1 Platform Framing 9-27 9.2.5.2 Concrete/Masonry 9-27 9.2.5.3 Moment-Resisting Frames 9-28 9.2.6 Roof Shape 9-30 9.3 Breakaway Wall Enclosures 9-30 9.4 Building Materials 9-33 9.4.1 Materials Below the DFE 9-34 9.4.2 Materials Above the DFE 9-35 9.4.3 Material Combinations 9-35 9.4.4 Fire Safety Considerations 9-36 9.4.5 Corrosion 9-37 9.5 Appurtenances 9-38 9.5.1 Decks and Covered Porches Attached to Buildings 9-38 9.5.1.1 Handrails 9-39 9.5.1.2 Stairways 9-39 9.5.2 Access to Elevated Buildings 9-39 9.5.3 Pools and Hot Tubs 9-40 9.6 References 9-43 COASTAL CONSTRUCTION MANUAL vii CONTENTS Volume II Chapter 10. Designing the Foundation ;! 10-1 10.1 Foundation Design Criteria 10-2 10.2 Foundation Styles 10-2 10.2.1 Open Foundations 10-3 10.2.2 Closed Foundations 10-3 10.2.3 Deep Foundations 10-4 10.2.4 Shallow Foundations 10-4 10.3 Foundation Design Requirements and Recommendations 10-4 10.3.1 Foundation Style Selection 10-5 10.3.2 Site Considerations 10-5 10.3.3 Soils Data 10-5 10.3.3.1 Sources of Published Soils Data 10-6 10.3.3.2 Soils Data from Site Investigations 10-6 10.4 Design Process 10-10 10.5 Pile Foundations 10-11 10.5.1 Compression Capacity of Piles—Resistance to Gravity Loads 10-12 10.5.2 Tension Capacity of Piles 10-15 10.5.3 Lateral Capacity of Piles 10-18 10.5.4 Pile Installation 10-20 10.5.5 Scour and Erosion Effects on Pile Foundations 10-21 10.5.6 Grade Beams for Pile Foundations 10-23 10.6 Open/Deep Foundations 10-25 10.6.1 Treated Timber Pile Foundations 10-25 10.6.1.1 Wood Pile-to-Beam Connections 10-26 10.6.1.2 Pile Bracing 10-27 10.6.1.3 Timber Pile Treatment 10-31 10.6.2 Other Open/Deep Pile Foundation Styles 10-31 10.7 Open/Shallow Foundations 10-34 10.8 Closed/Shallow Foundations 10-35 10.9 Pier Foundations 10-36 10.9.1 Pier Foundation Design Examples 10-37 10.9.2 Pier Foundation Summary 10-45 10.10 References 10-46 viii COASTAL CONSTRUCTION MANUAL is 1 Volume II i CONTENTS Chapter 11. Designing the Building Envelope 11-1 11.1 Floors in Elevated Buildings 11-4 11.2 Exterior Doors 11-4 11.2.1 High Winds I 11-6 11.2.1.1 Loads and Resistance 11-6 11.2.1.2 Wind-Borne Debris 11-7 11.2.1.3 Durability 11-7 11.2.1.4 Water Infiltration 11-7 11.3 Windows and Sklylights 11-9 11.3.1 High Winds 11-9 11.3.1.1 Loads and Resistance 11-9 11.3.1.2 Wind-Borne Debris 11-10 11.3.1.3 Durability 11-13 11.3.1.4 Water Infiltration 11-14 11.3.2 Seismic 11-15 11.3.3 Hail 11-15 11.4 Non-Load-Bearing Walls, Wall Coverings, and Soffits 11-15 11.4.1 High Winds 11-16 11.4.1.1 Exterior Walls 11-16 11.4.1.2 Flashings 11-21 11.4.1.3 Soffits 11-22 11.4.1.4 Durability 11-23 11.4.2 Seismic 11-24 11.5 Roof Systems 11-24 11.5.1 Asphalt Shingles 11-25 11.5.1.1 High Winds 11-25 11.5.1.2 Hail 11-36 11.5.2 Fiber-Cement Shingles 11-36 11.5.2.1 High Winds ,1 11-37 11.5.2.2 Seismic 11-37 11.5.2.3 Hail 11-37 11.5.3 Liquid-Applied Membranes 11-37 11.5.3.1 High Winds 11-37 11.5.3.2 Hail 11-38 11.5.4 Tiles 11-38 COASTAL CONSTRUCTION MANUAL ix CONTENTS Volume II 11.5.4.1 High Winds ' 11-38 11.5.4.2 Seismic 11-43 11.5.4.3 Hail 11-45 11.5.5 Metal Panels and Metal Shingles 11-45 11.5.5.1 High Winds 11-45 11.5.5.2 Hail 11-46 11.5.6 Slate 11-46 11.5.6.1 High Winds 11-46 11.5.6.2 Seismic 11-47 11.5.6.3 Hail 11-47 11.5.7 Wood Shingles and Shakes 11-47 11.5.7.1 High Winds 11-47 11.5.7.2 Hail 11-48 11.5.8 Low-Slope Roof Systems 11-48 11.5.8.1 High Winds 11-49 11.5.8.2 Seismic 11-49 11.5.8.3 Hail 11-49 11.6 Attic Vents 11-49 11.7 Additional Environmental Considerations 11-52 11.7.1 Sun 11-52 11.7.2 Wind-Driven Rain 11-52 11.8 References 11-52 List of Figures 11-58 List of Tables 11-60 Chapter 12. Installing Mechanical Equipment and Utilities 12-1 12.1 Elevators 12-1 12.2 Exterior-Mounted Mechanical Equipment 12-2 12.2.1 High Winds 12-2 12.2.2 Flooding 12-3 12.2.3 Seismic Events 12-6 12.3 Interior Mechanical Equipment 12-6 12.4 Electric Utility, Telephone, and Cable TV Systems 12-6 12.4.1 Emergency Power 12-9 x COASTAL CONSTRUCTION MANUAL Volume II CONTENTS 12.5 Water and Wastewater Systems 12-10 12.5.1 Wells 12-10 12.5.2 Septic Systems 12-11 12.5.3 Sanitary Systems 12-11 12.5.4 Municipal Water Connections 12-12 12.5.5 Fire Sprinkler Systems 12-12 12.6 References 12-12 Chapter 13. Constructing the Building 13-1 13.1 Foundation Construction 13-2 13.1.1 Layout 13-2 13.1.2 Pile Foundations 13-5 13.1.3 Masonry Foundation Construction 13-8 13.1.4 Concrete Foundation Construction 13-10 13.1.5 Wood Foundation Construction 13-12 13.1.6 Foundation Material Durability 13-13 13.1.7 Field Preservative Treatment' 13-17 13.1.8 Substitutions 13-18 13.1.9 Foundation Inspection Points 13-18 13.1.10 Top Foundation Issues for Builders 13-18 13.2 Structural Frame 13-19 13.2.1 Structural Connections 13-19 13.2.2 Floor Framing 13-23 13.2.2.1 Horizontal Beams and Girders 13-24 13.2.2.2 Substitution of Floor Framing Materials 13-25 13.2.2.3 Floor Framing Inspection Points 13-25 13.2.3 Wall Framing 13-25 13.2.3.1 Substitution of Wall Framing Materials 13-27 13.2.3.2 Wall Framing Inspection Points 13-27 13.2.4 Roof Framing 13-27 13.2.4.1 Substitution of Roof Framing Materials 13-28 13.2.4.2 Roof Frame Inspection Points 13-28 13.2.5 Top Structural Frame Issues for Builders 13-28 13.3 Building Envelope 13-29 13.3.1 Substitution of Building Envelope Materials 13-30 COASTAL CONSTRUCTION MANUAL xi CONTENTS 1 Volume II 13.3.2 Building Envelope Inspection Points 13-31 13.3.3 Top Building Envelope Issues for Builders 13-31 13.4 References 13-32 Chapter 14. Maintaining the Building 14-1 14.1 Effects of Coastal Environment 14-2 14.1.1 Corrosion 14-2 14.1.2 Moisture 14-3 14.1.3 Weathering 14-4 14.1.4 Termites 14-4 14.2 Building Elements That Require Frequent Maintenance 14-5 14.2.1 Glazing 14-7 14.2.2 Siding 14-7 14.2.3 Roofs 14-8 14.2.4 Exterior-Mounted Mechanical and,Electrical Equipment 14-9 14.2.5 Decks and Exterior Wood 14-9 14.2.6 Metal Connectors 14-10 14.3 Hazard-Specific Maintenance Techniques 14-11 14.3.1 Flooding 14-12 14.3.2 Seismic and Wind 14-12 14.4 References 14-13 Chapter 15. Retrofitting Buildings for Natural Hazards 15-1 15.1 Wildfire Mitigation 15-2 15.2 Seismic Mitigation 15-5 15.3 Flood Mitigation 15-8 15.3.1 Elevation 15-8 15.3.2 Relocation 15-10 15.3.3 Dry Floodproofing 15-11 15.3.4 Wet Floodproofing 15-12 15.3.5 Floodwalls and Levees 15-13 15.3.6 Multihazard Mitigation 15-14 15.4 High-Wind Mitigation 15-15 xii COASTAL CONSTRUCTION MANUAL Volume II CONTENTS 15.4.1 Evaluating Existing Homes 15-16 15.4.2 Wind Retrofit Mitigation Packages 15-16 15.4.2.1 Basic Mitigation Package 15-17 15.4.2.2 Intermediate Mitigation Package 15-19 15.4.2.3 Advanced Mitigation Package 15-19 15.4.2.4 Additional Mitigation Measures 15-19 15.4.3 FEMA Wind Retrofit Grant Programs 15-19 15.5 References 15-21 Acronyms A-1 Glossary G-1 Index I-1 List of Figures Chapter 7 Figure 7-1. Design framework for a successful building, incorporating cost, risk tolerance, use, location, materials, and hazard resistance 7-3 Figure 7-2. Average damage per structure vs. distance from the Florida Coastal Construction Control Line for Bay County, FL 7-4 Figure 7-3. Basic benefit-cost model 7-12 Chapter 8 Figure 8-1. Summary of typical loads and characteristics affecting determination of design load 8-2 Figure 8-2. Examples of tributary areas for different structural elements 8-4 Figure 8-3. Flowchart for estimating maximum likely design stillwater flood depth at the site 8-7 Figure 8-4. Erosion's effects on ground elevation 8-8 Figure 8-5. Parameters that are determined or affected by flood depth 8-9 Figure 8-6. Velocity versus design stillwater flood depth 8-17 Figure 8-7. Lateral flood force on a vertical component 8-19 COASTAL CONSTRUCTION MANUAL xiii CONTENTS Volume II Figure 8-8. Vertical (buoyant) flood force 8-20 Figure 8-9. Breaking wave pressure distribution against a vertical wall 8-23 Figure 8-10. Wave crests not parallel to wall 8-24 Figure 8-11. Water depth versus wave height, and water depth versus breaking wave force against, a vertical wall 8-25 Figure 8-12. Lateral wave slam against an elevated building 8-26 Figure 8-13. Hydrodynamic loads on a building 8-28 Figure 8-14. Scour at single vertical foundation member, with and without underlying scour resistant stratum 8-34 Figure 8-15. Deep scour around foundation piles, Hurricane Ike 8-35 Figure 8-16. Scour around a group of foundation piles 8-36 Figure 8-17. Effect of wind on an enclosed building and a building with an opening 8-48 Figure 8-18. Distribution of roof, wall, and internal pressures on one-story, pile-supported building 8-49 Figure 8-19. Variation of maximum negative MWFRS pressures based on envelope procedures for low-rise buildings 8-51 Figure 8-20. Components and cladding wind pressures 8-62 Figure 8-21. Effect of seismic forces on supporting piles 8-69 Chapter 9 Figure 9-1. Load path failure at gable end 9-2 Figure 9-2. Load path failure in connection between home and its foundation 9-2 Figure 9-3. Roof framing damage and loss due to load path failure at top of wall/roof structure connection 9-3 Figure 9-4. Load path failure in connections between roof decking and roof framing 9-3 Figure 9-5. Newer home damaged from internal pressurization and inadequate connections 9-4 Figure 9-6. Example load path for case study building 9-5 Figure 9-7. Connection of the roof sheathing to the roof framing (Link#1) 9-6 Figure 9-8. Connection of roof framing to exterior wall (Link#2) 9-8 Figure 9-9. Connection of truss to wood-frame wall 9-10 xiv COASTAL CONSTRUCTION MANUAL Volume II CONTENTS Figure 9-10. Roof truss-to-masonry wall connectors embedded into concrete-filled or grouted masonry cell 9-11 Figure 9-11. Connection of wall top plate-to-wall stud (Link#3) 9-11 Figure 9-12. Wall top plate-to-wall stud metal connector 9-12 Figure 9-13. Connection of wall sheathing to window header (Link#4) 9-13 Figure 9-14. Connection of window header to exterior wall (Link#5) 9-13 Figure 9-15. Connection of wall to floor framing (Link#6) 9-15 Figure 9-16. Connection of floor framing to support beam (Link#7) 9-17 Figure 9-17. Metal joist-to-beam connector 9-17 Figure 9-18. Connection of floor support beam to foundation (Link#8) 9-19 Figure 9-19. Diaphragm stiffening and corner pile bracing to reduce pile cap rotation 9-20 Figure 9-20. Shear wall holddown connector with bracket attached to a wood beam 9-24 Figure 9-21. Gable-end failure 9-25 Figure 9-22. Gable-end bracing detail; nailing schedule, strap specification, brace spacing, and overhang limits should be adapted for the applicable basic wind speed 9-26 Figure 9-23. Example of two-story platform framing on a pile-and-beam foundation 9-28 Figure 9-24. Two-story masonry wall with wood floor and roof framing 9-29 Figure 9-25. Steel moment frame with large opening 9-29 Figure 9-26. Gable-end failure caused by high winds 9-31 Figure 9-27. Hip roof that survived high winds with little to no damage 9-31 Figure 9-28. Typical failure mode of breakaway wall beneath an elevated building 9-32 Figure 9-29. Breakaway wall panel prevented from breaking away cleanly'by utility penetrations 9-32 Figure 9-30. Lattice beneath an elevated house in Zone V 9-33 Figure 9-31. House being constructed with a steel frame on wood piles 9-36 Figure 9-32. Townhouse framing system 9-37 Figure 9-33. Recommendations for orientation of in-ground pools 9-41 Figure 9-34. Recommended contraction joint layout for frangible slab-on-grade below elevated building 9-42 COASTAL CONSTRUCTION MANUAL xv CONTENTS 9 Volume II Chapter 10 Figure 10-1. Closed foundation failure due to erosion and scour undermining 10-4 Figure 10-2. Near collapse due to insufficient pile embedment 10-13 Figure 10-3. Surviving pile foundation 10-13 Figure 10-4. Deflected pile shape for an unbraced pile 10-19 Figure 10-5. Pier installation methods 10-20 Figure 10-6. Scour and erosion effects on piling embedment 10-21 Figure 10-7. Column connection failure 10-24 Figure 10-8. Scour around grade beam 10-25 Figure 10-9. Profile of timber pile foundation type 10-26 Figure 10-10. Diagonal bracing using dimensional lumber 10-28 Figure 10-11. Diagonal bracing schematic 10-28 Figure 10-12. Knee bracing 10-30 Figure 10-13. Section view of a steel pipe pile with concrete column and grade beam foundation type 10-32 Figure 10-14. Section view of a foundation constructed with reinforced concrete beams and columns to create portal frames 10-33 Figure 10-15. Profile of an open/shallow foundation 10-34 Figure 10-16. Stem wall foundation design 10-36 Figure 10-17. Performance comparison of pier foundations 10-37 Figure 10-18. Pier foundation and spread footing under gravity loading 10-38 Figure 10-19. Pier foundation and spread footing exposed to uplift forces 10-38 Figure 10-20. Pier foundation and spread footing exposed to uplift and lateral forces 10-39 Chapter 11 Figure 11-1. Good structural system performance but the loss of shingles, underlayment, siding, housewrap, and soffts resulted in significant interior water damage 11-2 Figure 11-2. Numerous wind-borne debris scars and several missing asphalt shingles 11-3 xvi COASTAL CONSTRUCTION MANUAL • Volume II CONTENTS Figure 11-3. House that survived a wildfire due in part to fire-resistant walls and roof while surrounding houses were destroyed 11-3 Figure 11-4. Plywood panels on the underside of a house that blew away because of excessive nail spacing 11-5 Figure 11-5. Sliding glass doors pulled out of their tracks by wind suction 11-5 Figure 11-6. Garage door blown from its track as a result of positive pressure 11-6 Figure 11-7. A 3/8-inch gap between the threshold and door which allowed wind-driven rain to enter the house 11-8 Figure 11-8. Window frame pulled out of the wall because of inadequate window frame attachment 11-9 Figure 11-9. Very old building with robust shutters constructed of 2x4 lumber, bolted connections, and heavy metal hinges 11-10 Figure 11-10. Unprotected cupola window that was broken 11-11 Figure 11-11. Design pressure and impact-resistance information in a permanent window label 11-12 Figure 11-12. Roll-up shutter slats that detached from the tracks 11-12 Figure 11-13. Shutter punctured by roof tile 11-13 Figure 11-14. House in Puerto Rico with metal jalousie louvers 11-14 Figure 11-15. Blown-off vinyl siding and foam sheathing; some blow-off of interior gypsum board 11-17 Figure 11-16. Blown-off fiber cement siding; broken window 11-18 Figure 11-17. Four brick veneer failure modes; five corrugated ties that were not embedded in the mortar joints 11-18 Figure 11-18. Typical EIFS assemblies 11-19 Figure 11-19. Blown-off EIFS, resulting in extensive interior water damage; detachment of the gypsum board or stud blow off; two windows broken by debris 11-20 Figure 11-20. Collapse of the breakaway wall, resulting in EIFS peeling 11-21 Figure 11-21. EIFS with a barrier design: blown-off roof decking; severely rotted OSB due to leakage at windows 11-22 Figure 11-22. Blown-away soffit,which allowed wind-driven rain to enter the attic 11-23 Figure 11-23. Blow-off of several newer shingles on a roof that had been re-covered by installing new asphalt shingles on top of old shingles 11-25 COASTAL CONSTRUCTION MANUAL xvii CONTENTS Volume II Figure 11-24. Small area of sheathing that was exposed after loss of a few shingles and some underlayment 11-26 Figure 11-25. Typical underlayment attachment 11-26 Figure 11-26. Enhanced underlayment Option 1, first variation: self-adhering modified bitumen over the sheathing 11-27 Figure 11-27. Enhanced underlayment Option 1,'second variation: self-adhering modified bitumen over the felt 11-28 Figure 11-28. House that used enhanced underlayment Option 3 with taped sheathing joints. The self-adhering modified bitumen tape was stapled because of bonding problems 11-29 Figure 11-29. Underlayment that was not lapped over the hip 11-30 Figure 11-30. Loss of shingles and underlayment along the eave and loss of a few hip shingles 11-31 Figure 11-31. Loss of shingles and underlayment along the rake 11-31 Figure 11-32. Incorrect installation of the starter course 11-32 Figure 11-33. Uplift loads along the rake that are transferred to the ends of the rows of self-sealing adhesive 11-33 Figure 11-34. A bleeder strip that was used at a rake blow-off 11-34 Figure 11-35. Inadequate sealing of the self-sealing adhesive at a hip 11-34 Figure 11-36. Proper and improper location of shingle fasteners (nails) 11-35 Figure 11-37. Proper and improper location of laminated shingle fasteners (nails) 11-35 Figure 11-38. Shingles that unzipped at the band lines 11-36 Figure 11-39. Blow-off of eave and hip tiles and some broken tiles in the field of the roof 11-39 Figure 11-40. Large area of blown-off underlayment on a mortar-set tile roof 11-39 Figure 11-41. Blow-off of wire-tied tiles installed over a concrete deck 11-39 Figure 11-42. Extensive blow-off of mortar-set tiles 11-40 Figure 11-43. Blown-offadhesive-set tile 11-40 Figure 11-44. Adhesive that debonded from the cap sheet 11-41 Figure 11-45. Blow-off of mechanically attached tiles 11-41 Figure 11-46. Blow-off of hip tiles that were nailed to a ridge board and set in mortar 11-42 xviii COASTAL CONSTRUCTION MANUAL Volume II CONTENTS Figure 11-47. Damage to field tiles caused by tiles from another area of the roof, including a hip tile 11-42 Figure 11-48. The fastener heads on this mechanically attached tile roof had corroded 11-43 Figure 11-49. Area of the roof where tiles were not nailed to batten strips 11-44 Figure 11-50. Tiles that were nailed to thin wood sheathing 11-44 Figure 11-51. Tile that slipped out from under the hip tiles 11-45 Figure 11-52. Blow-off of one of the nailers caused panels to progressively fail; cantilevered condenser platform; broken window 11-46 Figure 11-53. Damaged slate roof with nails that typically pulled out of the deck 11-47 Figure 11-54. Loss of wood shingles due to fastener corrosion 11-48 Figure 11-55. Method for maintaining a continuous load path at the roof ridge by nailing roof sheathing 11-50 Figure 11-56. Holes drilled in roof sheathing for ventilation and roof diaphragm action is maintained 11-51 Chapter 12 Figure 12-1. Condenser damaged as a result of insufficient elevation, Hurricane Georges (U.S. Gulf Coast, 1998) 12-4 Figure 12-2. Proper elevation of an air-conditioning condenser in a floodprone area; additional anchorage is recommended 12-4 Figure 12-3. Small piles supporting a platform broken by floodborne debris 12-5 Figure 12-4. Electric service meters and feeders that were destroyed by floodwaters during Hurricane Opal (1995) 12-7 Figure 12-5. Recommended installation techniques for electric and plumbing lines and utility elements 12-8 Figure 12-6. Damage caused by dropped overhead service, Hurricane Marilyn (U.S. Virgin Islands, 1995) 12-9 Chapter 13 Figure 13-1. Site layout 13-3 Figure 13-2. Typical pile notching process 13-4 Figure 13-3. Improper overnotched wood pile 13-4 COASTAL CONSTRUCTION MANUAL xix 1 CONTENTS Volume II Figure 13-4. Properly notched pile { 13-5 Figure 13-5. Typical wood pile foundation 13-6 Figure 13-6. Open masonry foundation 13-10 Figure 13-7. Concrete foundation 13-11 Figure 13-8. Concrete house 13-11 Figure 13-9. Wood decay at the base of a post supported by concrete 13-14 Figure 13-10. Examples of minimizing the least dimension of wood contact surfaces 13-15 Figure 13-11. Drip cut to minimize horizontal water movement along the bottom surface of a wood member 13-15 Figure 13-12. Exposure of end grain in stair stringer cuts 13-16 Figure 13-13. Deterioration in a notched stair stringer 13-16 Figure 13-14. Alternative method of installing stair treads 13-17 Figure 13-15. Connector failure caused by insufficient nailing 13-20 Figure 13-16. Reinforcement of overnotched piles 13-21 Figure 13-17. Beam support at misaligned piles 13-22 Figure 13-18. Proper pile notching for two-member and four-member beams 13-22 Figure 13-19. Proper use of metal twist strap ties; solid blocking between floor joists 13-23 Figure 13-20. Engineered joists used as floor joists with proper metal brace to keep the bottoms of the joists from twisting; engineered wood beam 13-24 Figure 13-21. Acceptable locations for splices in multiple-member girders 13-25 Figure 13-22. Full-height sheathing to improve transfer of shear 13-26 Chapter 14 Figure 14-1. Pile that appears acceptable from the exterior but has interior decay 14-1 Figure 14-2. Wood decay behind a metal beam connector 14-3 Figure 14-3. Severely corroded deck connectors 14-11 Figure 14-4. Deteriorated wood sill plate 14-12 xx COASTAL CONSTRUCTION MANUAL Volume II `1 CONTENTS Chapter 15 Figure 15-1. The three concentric zones of defensible space 15-2 Figure 15-2. The building envelope 15-3 Figure 15-3. Fire spreads vertically through vegetation 15-3 Figure 15-4. FEMA P-737, Home Builder's Guide to Construction in Wildlife Zones: Technical Fact Sheet Series 15-4 Figure 15-5. FEMA 232, Homebuilders Guide to Earthquake Resistant Design and Construction 15-5 Figure 15-6. A house with severe damage due to cripple wall failure 15-6 Figure 15-7. Common open-front configurations in one- and two-family detached houses 15-7 Figure 15-8. FEMA 530, Earthquake Safety Guide for Homeowners 15-8 Figure 15-9. Home elevated on piles 15-9 Figure 15-10. Preparing a building for relocation 15-10 Figure 15-11. Dry floodproofed structure 15-11 Figure 15-12. Wet floodproofed structure ; 15-13 Figure 15-13. Home protected by a floodwall and a levee 15-15 Figure 15-14. FEMA P-804, Wind Retrofit Guide for Residential Buildings 15-15 Figure 15-15. Wind Retrofit Mitigation Packages 15-17 Figure 15-16. Bracing gable end overhangs 15-18 Figure 15-17. Sprayed polyurethane foam adhesive to secure roof deck panels 15-18 Figure 15-18. Continuous load path for wind-uplift of a residential, wood-frame building 15-20 Figure 15-19. HMA grant process 15-21 List of Tables Chapter 7 Table 7-1. Examples of Flood and Wind Mitigation Measures 7-8 Table 7-2. Sample NFIP Flood Insurance Premiums for Buildings in Zone A 7-19 COASTAL CONSTRUCTION MANUAL xxi CONTENTS Volume II Table 7-3. Sample NFIP Flood Insurance Premiums for Buildings in Zone V Free of Obstruction Below the Lowest Floor 7-19 Table 7-4. Sample NFIP Flood Insurance Premiums for Buildings in Zone V with Obstruction Below the Lowest Floor 7-20 Chapter 8 Table 8-1. Value of Dynamic Pressure Coefficient (Cp) as a Function of Probability of Exceedance 8-23 Table 8-2. Drag Coefficients for Ratios of Width to Depth (w/d) and Width to Height (w/h) 8-29 Table 8-3. Depth Coefficient (CD) by Flood Hazard Zone and Water Depth 8-33 Table 8-4. Values of Blockage Coefficient CB 8-33 Table 8-5. Selection of Flood Loads for Fa in ASCE 7-10 Load Combinations for Global Forces 8-37 Table 8-6. Roof Uplift Connector Loads at Building Edge Zones 8-53 Table 8-7. Lateral Diaphragm Load from Wind Perpendicular to Ridge 8-53 Table 8-8. Roof and Wall Sheathing Suction Loads 8-63 Table 8-9. Lateral Connector Loads from Wind at Building End Zones 8-63 Chapter 9 Table 9-1. General Guidance for Selection of Materials 9-33 Chapter 10 Table 10-1. Foundation Styles in Coastal Areas' 10-3 Table 10-2. ASTM D2487 10-Soil Classifications 10-8 Table 10-3. Advantages and Special Considerations of Three Types of Pile Materials 10-12 Table 10-4. Bearing Capacity Factors (Ng) 10-14 Table 10-5. Earth Pressure Coefficients 10-14 Table 10-6. Friction Angle Between Soil and Pile (8) 10-15 Table 10-7. Allowable Compression and Tension of Wood Piles Based on Varying Diameters, Embedments, and Installation Methods 10-18 Table 10-8. Values of nh Modulus of Subgrade Reaction 10-19 xxii COASTAL CONSTRUCTION MANUAL ti Volume II CONTENTS Table 10-9. Advantages and Special Considerations of Pile Installation Methods 10-21 Table 10-10. Example Analysis of the Effects of Scour and Erosion on a Foundation 10-23 Chapter 11 Table 11-1. Allowable Basic Wind Speed'as a Function of Class 11-31 Chapter 13 Table 13-1. Foundation and Floor Framing Inspection Points 13-18 Table 13-2. Wall Inspection Points 13-27 Table 13-3. Roof Frame Inspection Points 13-29 Table 13-4. Building Envelope Inspection Points 13-31 Chapter 14 Table 14-1. Maintenance Inspection Checklist 14-5 Chapter 15 Table 15-1. Advantages and Disadvantages of Elevation 15-9 Table 15-2. Advantages and Disadvantages of Relocation 15-10 Table 15-3. Advantages and Disadvantages of Dry Floodproofing 15-12 Table 15-4. Advantages and Disadvantages of Wet Floodproofing 15-13 Table 15-5. Advantages and Disadvantages of a Floodwall or Levee 15-14 List of Equations Chapter 8 Equation 8.1. Design Stillwater Flood Depth 8-10 Equation 8.2. Design Flood Velocity 8-16 Equation 8.3. Lateral Hydrostatic Load 8-18 Equation 8.4. Vertical (Buoyant) Hydrostatic Force 8-19 Equation 8.5. Breaking Wave Load on Vertical Piles 8-21 COASTAL CONSTRUCTION MANUAL xxiii 9 1 CONTENTS ; Volume II Equation 8.6. Breaking Wave Load on Vertical Walls 8-22 Equation 8.7. Lateral Wave Slam 8-26 Equation 8.8. Hydrodynamic Load (for All Flow Velocities) 8-29 Equation 8.9. Debris Impact Load 8-32 Equation 8.10. Localized Scour Around a Single Vertical Pile 8-35 Equation 8.11. Total Localized Scour Around Vertical Piles 8-36 Equation 8.12. Total Scour Depth Around Vertical Walls and Enclosures 8-37 Equation 8.13. Velocity Pressure 8-50 Equation 8.14. Design Wind Pressure for Low-Rise Buildings 8-50 Equation 8.15. Seismic Base Shear by Equivalent Lateral Force Procedure 8-69 Equation 8.16. Vertical Distribution of Seismic Forces 8-70 Chapter 10 Equation 10.1. Sliding Resistance 10-10 Equation 10.2. Ultimate Compression Capacity of a Single Pile 10-14 Equation 10.3. Ultimate Tension Capacity of a Single Pile 10-15 Equation 10.4. Load Application Distance for an Unbraced Pile 10-19 Equation 10.5. Determination of Square Footing Size for Gravity Loads 10-40 Equation 10.6. Determination of Soil Pressure 10-43 Chapter 13 Equation 13.1. Pile Driving Resistance for Drop Hammer Pile Drivers 13-8 List of Examples Chapter 8 Example 8.1. Design Stillwater Flood Depth Calculations 8-11 Example 8.2. Wave Slam Calculation 8-27 Example 8.3. Hydrodynamic Load on Piles versus Breaking Wave Load on Piles 8-30 xxiv COASTAL CONSTRUCTION MANUAL Volume II s CONTENTS Example 8.4. Flood Load Example Problem 8-38 Example 8.5. Roof Uplift Connector Loads 8-54 Example 8.6. Lateral Diaphragm Loads from Wind Perpendicular to Ridge 8-57 Example 8.7. Roof Sheathing Suction Loads 8-64 Example 8.8. Lateral Connection Framing Loads from Wind 8-66 Example 8.9. Seismic Load 8-70 Example 8.10. Load Combination Example Problem 8-75 Chapter 9 Example 9.1. Roof Sheathing Nail Spacing:for Wind Uplift 9-6 Example 9.2. Roof-to-Wall Connection for,Uplift 9-9 Example 9.3. Uplift and Lateral Load Path at Window Header 9-14 Example 9.4. Uplift and Lateral Load Path at Wall-to-Floor Framing 9-15 Example 9.5. Uplift Load Path at Floor to Support Beam Framing 9-18 Example 9.6. Uplift Load Path for Support'Beam-to-Pile 9-19 Example 9.7. Uplift and Compression Due.to Shear Wall Overturning 9-21 Chapter 10 Example 10.1. Calculation for Allowable Capacities of Wood Piles 10-16 Example 10.2. Diagonal Brace Force 10-29 Example 10.3. Pier Footing Under Gravity Load 10-40 Example 10.4. Pier Footing Under Uplift Load 10-42 Example 10.5. Pier Footing Under Uplift and Lateral Loads 10-44 List of Worksheets Chapter 8 Worksheet 1. Flood Load Computation Non Tsunami Coastal A Zones (Solid Foundation) 8-44 COASTAL CONSTRUCTION MANUAL xxv I9 CONTENTS s Volume II . a Worksheet 2. Flood Load Computation Non Tsuy amic Zone V and Coastal A Zone (Open Foundation) 8-46 Worksheet 3. Load Combination Computation 8-80 xxvi COASTAL CONSTRUCTION MANUAL COASTAL CONSTRUCTION MANUAL .., a -,... "*. f..:i•I . Irre 4.11.: #111 , 7 ... 4 �' $t� rtry illiiiu timemaiiii, ..m! � i t I C I - 111 ,, � J `„'IE i rrriol, , ::-vi:.e......:' Pre - Design Considerations This chapter provides an overview of the issues that should be - considered before the building is designed. CROSS REFERENCE Coastal development has increased in recent years, and some For resources that augment of the sites that are chosen for development have higher risks of the guidance and other impact from natural hazards than in the past. Examples of sites information in this Manual, see the Residential Coastal with higher risks are those that are close to the ocean, on high Construction Web site(http:// bluffs that are subject to erosion, and on artificial fill deposits. www.fema.gov/rebuild/mat/ In addition, many of the residential buildings constructed today fema55.shtm). are larger and more costly than before, leading to the potential for larger economic losses if disaster strikes. However, studies conducted by the Federal Emergency Management Agency (FEMA) and others after major coastal disasters have consistently shown that coastal residential buildings that are properly sited, designed, and constructed have generally performed well during natural hazard events. Important decisions need to be made prior to designing the building. The decisions should be based on an understanding of regulatory requirements, the natural hazard and other risks associated with constructing a building on a particular site (see Chapter 4), and the financial implications of the decisions. The financial implications of siting decisions include the cost of hazard insurance, degree of hazard resistance and sustainability in the design, and permits and inspections. COASTAL CONSTRUCTION MANUAL 7-1 7 PRE-DESIGN CONSIDERATIONS Volume II Once a site has been selected, decisions must be ;made concerning building placement, orientation, and design. These decisions are driven primarily by the following: I Owner, designer, and builder awareness of natural hazards [ Risk tolerance of the owner r Aesthetic considerations (e.g., building appearance, proximity to the water,views from within the building, size and number of windows) Q Building use (e.g., full-time residence, part-time residence, rental property) E= Requirements of Federal, State, and local regulations and codes = Initial and long-term costs The interrelationships among aesthetics, building use, regulatory and code requirements, and initial cost become apparent during siting and design, and decisions are made according to the individual needs or goals of the property owner, designer, or builder. However, an understanding of the effect of these decisions on long-term and operational costs is often lacking. The consequences of the decisions can range from increased maintenance and utility costs to the ultimate loss of the building. The goal of this Manual is to provide the reader with an understanding of these natural hazards and provide guidance on concepts for designing a more hazard-resistant residential building. 7.1 Design Process The design process includes a consideration of the types of natural hazards that occur in the area where the building site is located and the design elements that allow a building to effectively withstand the potential damaging effects of the natural hazards (see Figure 7-1). The intent of this Manual is to provide sufficient technical information, including relevant examples, to help the designer effectively design a coastal residential building. This Manual does not describe all combinations of loads, types of material, building shapes and functions, hazard zones, and elevations applicable to building design in the coastal environment. The designer must apply engineering judgment to a range of problems. In addition, good design by itself is not enough to guarantee a high-quality structure. Although designing building components to withstand site-specific loads is important, a holistic approach that also includes good construction, inspection, and maintenance practices can lead to a more resilient structure. Before designing a building and to optimize the usefulness of Volume II of this Manual, the designer should obtain the codes and standards, such as ASCE 7 and ASCE 24, that are listed in the reference section of each chapter and other relevant information such as locally adopted building codes and appropriate testing protocols. Although codes and standards provide minimums, the designer may pursue a higher standard. Many decisions require the designer's judgment, but it is never appropriate to use a value or detail that will result in a building that is not constructed to code. 7-2 COASTAL CONSTRUCTION MANUAL Volume II PRE-DESIGN CONSIDERATIONS 7 Funding Risk Tolerance Figure 7-1. Design framework for Building Use a successful building, • Layout incorporating cost, risk Design Premise Design • Function tolerance, use, location, Anticipated loads • Continous load paths materials, and hazard must be transferred Location resistance through the building • Resist or avoid • Hazards• in continuous paths hazards • Loads/conditions to the supporting soils.An • Conditions greater ! • Regulations weaknesses in than design • Building codes the continuous conditions j and standards paths are potential • Constructability points of failure ! Materials • Durability - -- •Appearance • Maintenance Successful Building Volume II contains many design equations, but they do not cover all of the design calculations that are necessary and are provided only as examples: 7.2 Design Requirements The minimum design requirements for loads, materials, and material resistances for a given building design are normally specified in the locally adopted building code. Nothing in this Manual is intended to recommend the use of materials or systems outside the uses permitted in building code requirements. The loads used in this Manual are based on ASCE 7-10, which is the reference load standard in model building codes. Material and material resistance requirements cited in this Manual are based on the minimum requirements of applicable building codes. However, designers are encouraged throughout the Manual to seek out information on loads and materials that exceed the minimum requirements of the building code. Other sources of information for loads and materials are also provided. 7.3 Determining the Natural Hazard Risk Assessing risk to coastal buildings and building sites requires identifying or delineating hazardous areas and considering the following factors: Types of hazards known to affect a region Li Geographic variations in hazard occurrence and severity 11 Methods and assumptions underlying existing hazard identification maps or products COASTAL CONSTRUCTION MANUAL 7-3 7 PRE-DESIGN CONSIDERATIONS Volume II [ "Acceptable" level of risk 0 Consequences of using (or not using) recommended siting, design, and construction practices Geographic variations in coastal hazards occur, both along and relative (perpendicular) to the coastline. Hazards affecting one region of the country may not affect another. Hazards such as wave loads,which affect construction close to the shoreline, usually have a lesser or no effect farther inland. For example, Figure 7-2 shows how building damage caused by Hurricane Eloise in 1975 was greatest at the shoreline but diminished rapidly in the inland direction. The figure represents data from only one storm but shows the trend of a typical storm surge event on coastlines (i.e., damage decreases significantly as wave height decreases). The level of damage and distance landward are dictated by the severity of the storm and geographic location. Through Flood Insurance Studies (FISs) and FloodInsurance Rate Maps (FIRMs), FEMA provides detailed coastal flood hazard information (see Section 3.5).'However, these products reflect only flood hazards and do not include a consideration of a number of other hazards that affect coastal areas. Other Federal agencies and some states and communities have completed additional coastal hazard studies and delineations. The Residential Coastal Construction Web site (h'ttp://www.fema.gov/rebuild/mat/fema55.shtm) provides introductory information concerning more than 25 hazard zone delineations developed by or for individual communities or states (see "Web Sites for Information about Storms, Big Waves, and Water Level"). Some delineations have been incorporated into mandatory siting and/or construction requirements. When reviewing the hazard maps and delineations that are provided on the Residential Coastal Construction Web site, designers should be aware that coastal hazards are often mapped using different levels of risk or recurrence intervals. Thus, the consistent and acceptable level of risk (the level of risk judged by the designer to be appropriate for a particular building) should be considered early in the planning and design process (see Chapter 6). The hazard maps and delineations are provided as a historical reference only. The most up-to-date information can be obtained by contacting local officials. Figure 7-2. Average damage per structure(in thousands a 200 . Florida oastal of 1975 dollars)versus Construction distance from the Florida :L Control Line Coastal Construction 160 Control Line for Bay o.y Seaward Landward County, FL, Hurricane 0-0 Eloise(Florida, 1975) m 120 1= is SOURCE:ADAPTED FROM e0 O SHOWS 1978 r I. .. 480 . 0 v f rn f F. :40.. 0 -150 -100 -50 0 50 100 150 Distance from Coastal Construction Control Line(in feet) 7-4 COASTAL CONSTRUCTION MANUAL Volume II PRE-DESIGN CONSIDERATIONS 7 v 7.4 Losses Due to Natural Hazards in Coastal Areas It is easy for property owners to become complacent about the potential for a natural disaster to affect their properties. Hurricanes and earthquakes are generally infrequent events. A geographic area may escape a major hazard event for 20 or more years. Or,if an area has recently been affected, residents may believe the chances of a recurrence in the near future are remote.These perceptions are based on inaccurate assumptions and/or a lack of understanding of natural hazards and the risk of damage. I The population and property values along the U.S.coast are both rapidly increasing.Although better warning systems have reduced the number of fatalities and injuries associated with natural disasters, increases in the number and value of structures along the coast have dramatically increased potential property losses. From 2000 through 2009, there were 13 presidentially ttip declared disasters resulting from hurricanes and tropical uN „.......) systems, each causing more than $1 billion in losses. NOTE Hurricane Katrina in 2005 was the most expensive natural According to the Mortgage disaster in U.S. history, causing estimated economic losses Bankers Association (2006),from of more than $125 billion and insured losses of$35 billion, 1985 to 2005, hurricanes and surpassing Hurricane Andrews's $26.5 billion in losses in tropical storms accounted for the 1992. Other recent memorable storms are,Tropical Storm major nce l sf all catastrophic insurance losses.The percentages Allison (2001), Hurricane Rita (2005), Hurricane Wilma of property damage caused by (2005), Hurricane Ike (2008), and the 2004 hurricane i various catastrophic events during season in which four storms (Charley, Frances, Ivan, and this period were: Jeanne) affected much of the East Coast in both coastal and ! • 43.7 percent from inland areas. hurricane/tropical storms • 23.3 percent from Following Hurricane Andrew, which ravaged south Florida i wind/thunderstorms " in 1992, studies were conducted to determine,whether the i • 5.1 percent from earthquakes " damage suffered was attributable more to the intensity of the storm or to the location and type ,of development. Approximately 94.4 percent of all catastrophic events occurring According to the Insurance Institute for Business and Home i during this period were attributed ' Safety(IBHS): ! to natural disasters. Conservative estimates from claim studies reveal that approximately 25 percent of Andrew-caused insurance losses (about $4 billion) were attributable to construction that failed to meet the code due to poor enforcement, as well as shoddy workmanship. At the same time, concentrations of population and of property exposed to hurricane winds in southern Florida grew many-fold (IBHS 1999). After Hurricane Andrew, codes and regulations were enacted that support stronger building practices and wind protection. IBHS conducted a study in 2004 following Hurricane Charley that found: I ... homes built after the adoption of these new standards resulted in a decrease in the frequency and severity of damage to various building components. Furthermore, based on the analysis of additional living expense records, it is concluded that the new building code requirements allowed homeowners to return to their home more quickly and likely reduced the disruption of their day to day lives (IBHS 2004, p. 5). COASTAL CONSTRUCTION MANUAL : 7 5 7 PRE-DESIGN CONSIDERATIONS Volume II The past several decades have not resulted in major losses along the Pacific coast or Great Lakes, but periodic reminders support the need for maintaining a vigilant approach to hazard-resistant design for coastal structures in other parts of the country. In February 2009, the Hawaiian Islands and portions of California were under a tsunami watch. This type of watch occurs periodically in sections of northern California, Oregon, Washington, and Alaska and supports the need to construct buildings on elevated foundations. Although tsunamis on the Pacific coast may be less frequent than coastal hazard events on the Atlantic coast, ignoring the threat can result in devastating losses. Hazard events on the coastlines of the Great Lakes have resulted in damage to coastal structures and losses that are consistent with nor'easters on the Atlantic coast. Surge levels and high winds can occur every year on the Great Lakes,and it is important for designers to ensure that homeowners and builders understand the nature of storms on the Great Lakes. As in other regions, storm-related losses can result in the need to live in a house during lengthy repairs or be displaced for extended periods while the house is being repaired.The loss of irreplaceable possessions or property not covered by flood or homeowners insurance policies are issues a homeowner should be warned of and are incentives to taking a more hazard-resistant design approach. Chapters 2 and 3 contain more information about the hazards and risks associated with building in coastal areas. 7.5 Initial, Long-Term, and Operational Costs Like all buildings, coastal residential buildings have initial, long-term, and operational costs. C Initial costs include property evaluation, acquisition, permitting, design, and construction. c Long-term costs include preventive maintenance and repair and replacement of deteriorated or damaged building components.A hazard-resistant design can result in lower long-term costs by preventing or reducing losses from natural hazard events. L' Operational costs include costs associated with the use of the building, such as the cost of utilities and insurance. Optimizing energy efficiency may result in a higher initial cost but save in operational costs. In general, the decision to build in any area subject to significant natural hazards—especially coastal areas—increases the initial, long-term, and operational costs of building ownership. Initial costs are higher because the natural hazards must be identified, the associated risks assessed, and the building designed and constructed to resist damage from the natural hazard forces. Long-term costs are likely to be higher because a building in a high-risk area usually requires more frequent and more extensive maintenance and repairs than a building sited elsewhere. Operational costs are often higher,because of higher insurance costs and, in some instances, higher utility costs.Although these costs may seem higher, benefits such as potential reductions in insurance premiums and reduced repair time following a natural disaster may offset the higher costs. 7-6 COASTAL CONSTRUCTION MANUAL Volume II PRE-DESIGN CONSIDERATIONS 7 7.5.1 Cost Implications of Siting Decisions 0_00) COST The cost implications of siting decisions are as follows: CONSIDERATION n The closer buildings are sited to the water, the more likely Designers and homeowners they are to be affected by flooding, wave action, erosion, should recognize that erosion scour, debris impact, overwash, and corrosion. In addition, control measures can be wind speeds are typically higher along coastlines, particularly expensive, both initially and within the first several hundred feet inland. Repeated , In over somethe lifetimen sf a robsioing. p In instances, erosion exposure to these hazards, even when buildings are control costs can equal designed to resist their effects, can lead to increased long- ; or exceed the cost of the term costs for maintenance and damage repair. property or building being protected. 5 Erosion—especially long-term erosion—poses a serious _ threat to buildings near the water and on high bluffs above the floodplain. Wind-induced erosion can lower ground elevations around coastal buildings, exposing Zone V - - -.- buildings to higher-than-anticipated forces, and exposing Zone A buildings to Zone V flood hazards.Maintenance CROSS REFERENCE and repair costs are high for buildings in erosion hazard For information on siting areas, not only because of damage to the building, but coastal residential buildings, also because of the need for remedial measures (e.g., see Chapter 4. building relocation or erosion protection projects, such as _ - _, seawalls, revetments, and beach nourishment, where permitted). c; Sites nearest the water are likely to be in Zone V where building foundations, access stairs, parking slabs, and other components below the building are especially vulnerable to flood, erosion, and scour effects.As a result, the potential for repeated damage and repair is greater for Zone V buildings than buildings in other zones, and the buildings have higher flood insurance rates and increased operational costs. In addition, although elevating a building can protect the superstructure from flood damage, it may make the entire building more vulnerable to earthquake and wind damage. 7.5.2 Cost Implications of Design Decisions The cost implications of design decisions are as follows: NOTE E For aesthetic reasons, the walls of coastal buildings often Over the long term, poor siting include a large number of openings for windows and doors, decisions are rarely overcome especially in the walls that face the water. Designs of this by building design. type lead to greater initial costs to strengthen the walls and to protect the windows and doors from wind and - wind-borne debris (missiles). If adequate protection in the form of shutter systems or impact-resistant glazing is not provided, long-term costs are greater because of(1) the need to repair damage to glazing and secondary damage by the penetration of wind-driven rain and sea spray and/or (2) the need to install retrofit protection devices at a later date. COASTAL CONSTRUCTION MANUAL 7-7 7 PRE-DESIGN CONSIDERATIONS . Volume II C As explained in Chapter 5, National Flood InsuOnce Program (NFIP) regulations allow buildings in Coastal A Zones to be constructed on perimeter;wall (e.g., crawlspace) foundations or on earth fill. Open (pile, pier, or column) foundations are required only for Zone V buildings.Although a Coastal A Zone building on a perimeter wall foundation or fill may have a lower initial construction cost than a similar building on an open foundation, it may be subject to damaging waves, velocity flows, and/or erosion and scour over its useful life.As a result, the long-term costs for a building on a perimeter wall foundation or fill may actually be higher because of the increased potential for damage. n In an effort to reduce initial construction costs, designers may select building materials that require high levels of maintenance. Unfortunately, the initial savings are often offset because (1) coastal buildings, particularly those near bodies of saltwater, are especially prone to the effects of corrosion, and (2) owners of coastal buildings frequently fail to sustain the continuing and time-consuming levels of maintenance required. The net effect is often;increased building deterioration and sometimes a reduced capacity of structural and non-structural components to resist the effects of future natural hazard events. Table 7-1 provides examples of design elements and the cost considerations associated with implementing them. Although these elements may have increased costs when implementing them on a single building, developers may find that incorporating them into speculative houses with large-scale implementation can provide some savings. Table 7-1. Examples of Flood and Wind Mitigation Measures Mitigation Measure Cross Benefits/Advantages Costs/Other Considerations References(a) Adding 1 to 2 feet to the Reduces the potential May conflict with community required elevation of the for the structure to be building height restrictions; may lowest floor or lowest 5.4.2 damaged by waves and/ require additional seismic design horizontal structural 6.2.1.3 or floodwaters; reduces considerations; longer pilings member of the building flood insurance premiums may cost more i Increasing embedment 10.2.3 Adds.protection against Longer pilings may cost more depth of pile foundations 13.1.2 scours and erosion Improving flashing and Reduces water and wind Increases the number of weather-stripping around 11.4.1.2 infiltration into building important tasks for a contractor windows and doors to monitor ' Installing fewer breakaway Decreases potential for walls or more openings damage to understory of Reduces the ability to use in continuous foundation 5.4.2 structure; reduces amount understory structure for storage walls than currently noted of debris during storm for open foundations on the building plans event Elevating a building in a Coastal Zone A on an Reduces the potential open foundation or using 5.4.2 for the structure to be Breakaway walls still require only breakaway walls for 10.3.1 damaged by waves, flood openings in Zone A enclosures below the erosion, and floodwaters lowest floor 7-8 COASTAL CONSTRUCTION MANUAL Volume II PRE-DESIGN CONSIDERATIONS 7 Table 7-1. Examples of Flood and Wind Mitigation Measures (concluded) Mitigation Measure Cross Benefits/Advantages Costs/Other Considerations References(a) :Reduces the potential for damage from wind-borne Adding shutters for :debris impact during a Shutters require installation or glazing protection 11.3.1.2 storm event; reduces activation before a storm event ' potential for wind-driven rain water infiltration Using asphalt roof Reduces shingle blowoff High bond strength shingles are shingles with high bond 11.5.1 'during high winds slightly more expensive strength 7 " Instead of vinyl siding, I installing cladding systems that have passed a test Tested cladding systems These systems may cost more protocol that simulates 11.4.1.1 (reduce blowoff on walls than other materials and may design-level"fluctuating 14.2.2 during high winds require additional maintenance wind pressures(on a realistic installed wall specimen) Using metal connectors or fasteners with a thicker 14.1.1 ,Increases useful life of Thicker galvanized or stainless galvanized coating or 14.2.6 connectors and fasteners steel coatings are more costly connectors made of stainless steel i Installing roof sheathing; using a high-wind . prescriptive approach Reduces wind and water Minimal increased cost when for improved fasteners, 11.5-. damage to roof covering these tasks are done during a installing additional 15.3.1 • land interior from a severe reroofing project ' underlayments, or event improving roof covering details as required (a)Sections in this Manual COASTAL CONSTRUCTION MANUAL 7-9 7 PRE-DESIGN CONSIDERATIONS Volume II • DESIGNING FOR FLOOD LEVELS ABOVE THE BASE FLOOD ELEVATION (BFE) Designers and owners should consider designing buildings for flood levels above the BFE for the following reasons: • Floods more severe than the base flood can and do occur, and the consequences of flood levels above the BFE can be devastating. ; -- • Older FIRMs may not reflect current base flood hazards. , '1 • FIRMs do not account for the effect of future ,1 1, conditions flood hazards;future flood hazards , -;•- i a ).,` _..—_ may exceed present-day flood hazards because ;%' - U III II '* r of sea level rise, coastal erosion, and other a ,r P 4. 1 ' J - I �. factors. r ; l •a , • Buildings elevated above the BFE will sustain less I ffi , flood damage and will be damaged less often ' %-- .,. ,' ' ; a I �� Pg.:: than buildings constructed at the BFE. "1,,_ „} t. r • For a given coastal foundation type,the costs of f� ,a a ; building higher than the BFE are nominal when •t� r• . ,'f .+, a _- pi, °�t�� 1R, r rr.., f d(dF compared to reduced future costs to the owner. y�y * .; _C�` ; , WIN,pig • Flood damage increases rapidly with flood ,� ;r'"; "ilw -¢ - -'k-� elevation above the lowest floor, especially when '" 1^`- '" i waves are present: Lateral and vertical wave ' - "� `. '" • forces against elevated buildings("wave slam") - -�'-`� ,�` -_ , -- Y,. '.., can be large and destructive. Waves as small as .., *Y. 1, 1.5 feet high can destroy many residential walls. , �- � • Elevated buildings whose floor systems and r-- -* walls are submerged during a flood may enhance , _-- ti` foundation scour by constricting flow between the giu- elevated building and the ground. ` Z. c-p �i I."'- ...ter.. • Over a 50-year lifetime,the chance of a base flood r., , - -, - - - occurring is about 40 percent. For most coastal ilt°�•' �''"' "1-1- rt-- areas,the chance of a flood approximately 3 , - feet higher than the BFE occurring over 50 years '�'� - will only be about 10 percent. Designing and ' -Liik+- constructing to an elevation of BFE+3 feet is not •-. '' ' - - normally difficult. �,,, - f' It �" t' `1 it Y �' a • Owners whose buildings are elevated above -i1 - .I ., q �,6 the BFE can save significant amounts of money it- ,. „___ _ ' ' through reduced flood insurance premiums. '• '- Premiums can be reduced by up to 50 to 70 , '` ",- c-''% �- percent, and savings can reach several thousands .ram •_ _"--• `•'' I:I'll. of dollars per year in Zone V. >`- ` t ., F, 7-10 COASTAL CONSTRUCTION MANUAL Volume II PRE-DESIGN CONSIDERATIONS 7 i 7.5.3 Benefits and Cost Implications of Siting, Design, and Construction Decisions . This Manual is designed to help property ,owners manage some -r- of the risk associated with constructing a residential building -in a coastal area. As noted in Chapter 2, studies of the effects of CROSS REFERENCE natural disasters on buildings demonstrate that sound siting, design, engineering, construction, and maintenance practices are important For more information on factors in the ability of a building to survive a hazard event with designing coastal residential little or no damage. This chapter and the remainder of Volume II buildings, see Chapter 9. provide detailed information about how to site, design, construct, _ and maintain a building to help manage risks. Constructing to a model building code and complying with regulatory siting requirements provides a building with a certain level of protection against damage from natural hazards. However, compliance with minimum code and regulatory requirements'does not guarantee that a building is not at risk from a natural hazard. Exceeding code and minimum regulatory requirements provides an added measure of safety but also adds to the cost of construction,which must be weighed against the benefit gained. The often minimal initial cost of mitigation measures offers long-term benefits that provide a cost savings from damage avoided over the life of the building. Incorporating mitigation measures can reduce a homeowner's insurance premiums and better protect the building, its contents, and occupants during a natural hazard event, thus decreasing potential losses. Similar to cost reductions provided by the U.S. Green Building Council LEED[Leadership in Energy and Environmental Design])for Homes Reference Guide (USGBC 2009) and ICC 700-2008, incorporating hazard mitigation measures into a building may pay for themselves over a few years based on insurance premium savings and the improved energy efficiency that some of the techniques provide. Table 7-1 lists examples of flood and wind mitigation measures ' - - that can be taken to help a structure withstand natural hazard CROSS REFERENCE events. The need for and benefit of some mitigation measures are difficult to predict. For example, elevating a building above the Unless both questions design flood elevation (DFE) could add to the cost of the building. presented in Section 4.8 of this Manual (regarding This additional cost must be weighed against the probability of a I the acceptable level of flood or storm surge exceeding the DFE: Figure 7-3 illustrates residual risk at a site) can the comparative relationship between damage, project costs, and be answered affirmatively, benefits associated with a hazard mitigation project on a present- I the property owner should valuer basis over the life of the project. reconsider purchasing the property. 1 Present value is the current worth of future sums of money.For example,the present value of$100 to be received 10 years from now is about$38.55,using a discount rate equal to 10 percent interest compounded annually. COASTAL CONSTRUCTION MANUAL 7-11 1 7 PRE-DESIGN CONSIDERATIONS Volume II Figure 7-3. A Basic benefit-cost model ` I Net benefit=Money saved i by implementing mitigation Net that reduces damage benefit during a hazard event Cost of mitigation Cost of damage without A mitigation Cost of damage with mitigation 7.6 Hazard Insurance Insurance should never be viewed as an alternative to damage prevention. However, despite best efforts to manage NOTE risk, structures in coastal areas are always subject to potential Adamage duringa natural hazard event. Hazard insurance to by homeowners single-family home is covered g homeowners insurance, offset potential financial exposure is an important consideration and a multi-family building is for homeowners in coastal areas. Insurance companies base covered by a dwelling policy.A hazard insurance rates on the potential for a building to be homeowner policy is different damaged by various hazards and the predicted ability of the from a dwelling policy.A homeowner policy is a multi- building to withstand the hazards. Hazard insurance rates peril package policy that include the following considerations: automatically includes fire and allied lines, theft, and liability Type of building coverage. For a dwelling policy, peril coverages are purchased n Area of building footprint separately. In addition to Federal and private flood insurance,this L' Type of construction chapter focuses on homeowners insurance. 1 Location of building _ t_. Date of construction E' Age of the building 7-12 COASTAL CONSTRUCTION MANUAL Volume II PRE-DESIGN CONSIDERATIONS 7 Existence and effectiveness of a fire department and fire hydrants (or other dependable, year-round sources of water) Effectiveness of the building code and local building department at the time of construction Although designers and builders may not be able to control the rates and availability of insurance, they should understand the implications of siting and construction decisions on insurance costs and should make homeowners aware of the risk and potential expense associated with owning a house in a high-hazard area. Insurance considerations can and do affect the decisions about the placement and height of coastal buildings and the materials used in their construction. Input from an insurance industry representative during the design process, rather than after the completion of the building, can positively influence important decisions in addition to potentially saving homeowners;money on insurance premiums. Standard homeowners insurance policies cover multiple perils, including fire, lightning,hail, explosion, riot, smoke, vandalism, theft, volcanic eruption, falling objects, weight of snow, and freezing. Wind is usually (but not always) covered, and an endorsement can often be added for earthquake coverage. Homeowners insurance also includes liability coverage.A separate policy is normally required for flooding. 7.6.1 Flood Insurance As described in Chapter 5, flood insurance is offered through the (('� NFIP (see Section 6.2.2.1) in communities that participate in the NOTE program (e.g.,incorporated cities, towns,villages; unincorporated - - - areas of counties, parishes, and federally recognized Indian tribal Standard homeowners governments). This flood insurance is required as a condition normsu lye oo r s o not normally cover damage from of receiving federally backed, regulated, or insured financial flood or earth movement(e.g., assistance for the acquisition of buildings in Special Flood Hazard ' earthquakes, mudslides). Areas (SFHAs). This includes almost all mortgages secured by property in an SFHA. NFIP flood insurance is not available in communities that do not participate in the NFIP. Most coastal communities participate in the program because they recognize the risk of flood hazard events and the need for flood insurance. The following sections summarize how coastal buildings are rated for flood insurance and how premiums are established. 7.6.1.1 Rating Factors The insurance rate is a factor that is used to determine the - amount to be charged for a certain amount of insurance coverage, NOTE called the premium. Premiums are discussed in Section 7.6.1.3. The following seven rating factors are used for flood insurance NFIP regulations define basement as any area of coverage for buildings (not including contents): a building with the floor subgrade(i.e., below ground LI Building occupancy level)on all sides. 12 Building type r, Flood insurance zone COASTAL CONSTRUCTION MANUAL 7-13 7 PRE DESIGN CONSIDERATIONS Volume II Date of construction CROSS REFERENCE Elevation of lowest floor or bottom or the lowest horizontal - - structural member of the lowest floor For additional information about enclosures, the use r= Enclosures below the lowest floor of space below elevated buildings, and flood r_, Location of utilities and service equipment insurance, see Chapter 5. Building Occupancy The NFIP bases rates for flood insurance in part on four types of building occupancy: r_ Single-family L= Two-to four-family C Other residential E Non-residential Only slight differences exist among the rates for the three types of residential buildings. Building Type The NFIP bases rates for flood insurance in part on the following building-type factors: Li Number of floors (one floor or multiple floors) E Presence of a basement r- First floor elevation (whether the building is elevated and/or whether there is an enclosure below the lowest elevated floor) Manufactured home affixed to a permanent foundation NFIP flood insurance is generally more expensive for buildings with basements and for buildings with enclosures below BFE. Flood Insurance Zone The NFIP bases rates for flood insurance in part on flood insurance zones. The zones are grouped as follows for rating purposes: Zone V(V,VE, and V1—V30). The zone closest to the water, subject to "coastal high hazard flooding" (i.e., flooding with wave heights greater than 3 feet). Flood insurance is most expensive in Zone V because of the severity of the hazard. However,the zone is often not very wide. Zones V1—V30 were used on FIRMs until 1986. FIRMs published since then show Zone VE. 7-14 COASTAL CONSTRUCTION MANUAL Volume II PRE-DESIGN CONSIDERATIONS 7 Zone A(A,AE,AR,AO, and Al—A30). Coastal flood hazard areas where the wave -!` NOTE E_ heights are less than 3 feet. Zones Al—A30 - were used on FIRMs until 1986. FIRMs Because Zones B, C, and X designate areas published since then show Zone AE. outside the SFHA, construction in these zones is not subject to NFIP floodplain regulations. Homeowners in these areas, however, can Zones B, C, and X. The zones outside purchase Preferred Risk Policies of flood the 100-year floodplain or SFHA. Flood insurance.The rates in these areas are insurance is least expensive in these zones significantly lower than those in Zone V and and generally not required by mortgage Zone A. lenders. Zone B and Zone C were used on FIRMs until 1986. FIRMs published since then show Zone X. FIRMs show areas designated as being in the Coastal Barrier Resource System (CBRS) or "otherwise protected areas." These CROSS REFERENCE areas (known as "CBRA zones") are identified in the Coastal For more information about Barrier Resources Act (CBRA) and amendments. Flood insurance the CBRA and CBRS, see is available for buildings in these zones only if the buildings were Chapter 5. walled and roofed before the CBRA designation date shown in the FIRM legend and only if the community participates in the NFIP. Date of Construction In communities participating in the NFIP, '011 buildings constructed on or before the date NOTE of the first FIRM for that community or on Flood insurance is available through the NFIP for or before December 31, 1974, whichever the following types of buildings: single-family, is later, have flood insurance rates that are 2-to 4-family, other residential, and non- "grandfathered" or "subsidized." These residential buildings. Condominium policies are buildings are referred to as pre-FIRM. They also available. Designers may wish to consult are charged a flat rate based on building knowledgeable insurance agents and the Flood Insurance Manual(FEMA 2011)for policy details occupancy, building type, and flood and exclusions that affect building design and insurance zone. use.Additional information is available in FEMA FIA-2,Answers to Questions about the National The rates for buildings constructed after the Flood Insurance Program (2004). date of the first FIRM (post-FIRM buildings) are based on building occupancy, building type, flood insurance zone, and two additional factors: (1) elevation of the top of the lowest floor (in Zone A) or bottom of the lowest horizontal structural member of the lowest floor (in Zone V), and (2) enclosed areas below the lowest floor in an elevated building. If a pre-FIRM building is substantially improved (i.e., the value of the improvement exceeds 50 percent of the market value of the building before the improvement was made), it is rated as a post-FIRM building. If a pre-FIRM building is substantially damaged for any reason (i.e., the true cost of repairing the building to its pre-damaged condition exceeds 50 percent of the value of the building before it was damaged), it is also rated as a post-FIRM building regardless of the amount of repairs actually undertaken. The local building COASTAL CONSTRUCTION MANUAL 7-15 7 PRE-DESIGN CONSIDERATIONS Volume II official or floodplain administrator, not the insurance agent, determines whether a building is substantially improved or substantially damaged. If a building is determined to be substantially improved or substantially damaged, the entire structure must be brought into compliance with the current FIRM requirements. An additional insurance rate table is applied to buildings constructed in Zone V on or after October 1, 1981. The table differentiates between buildings with an obstruction below the elevated lowest floor and those without such an obstruction. Elevation of Lowest Floor or Bottom or Lowest Horizontal Structural Member of the Lowest Floor In Zone A, the rating for post-FIRM buildings is based on the `" elevation of the lowest floor in relation to the BFE. In Zone V, ,tr1/4),\ the rating for post-FIRM buildings is based on the elevation —7-7-4 WARNING of the bottom of the lowest floor's lowest horizontal structural Differences exist between what member in relation to the BFE. Flood insurance rates are lower • is permitted under floodplain for buildings elevated above the BFE. Rates are significantly management regulations and higher for buildings rated at 1 foot or more below the BFE. what is covered by NFIP flood insurance. Some building design Ductwork or electrical, plumbing, or mechanical components considerations should be guided under the lowest floor must either be designed to prevent water by floodplain management infiltration or elevated above the BFE. Additional elevation of requirements and by knowledge of the design's impact on flood the lowest floor may be required. . insurance policy premiums. Although allowable,some designs In Zone A, a building on a crawlspace must have openings ; that meet NFIP requirements will in the crawlspace walls that allow for the unimpeded flow of ' result in higher premiums. floodwaters more than 1-foot deep. If the crawlspace walls do i _ _ _ not have enough properly sized openings, the crawlspace is considered an enclosed floor, and the building may be rated as having its lowest floor at the elevation of the grade inside the crawlspace. Similarly, if furnaces and other equipment serving the building are below the BFE, the insurance agent must submit more information on the structure to the NFIP underwriting department before the policy's premium can be determined. Enclosures Below the Lowest Floor In Zone V, buildings built on or after October 31, 1981, are rated in one of three ways: COST CONSIDERATION 1. A building is rated as "free of obstruction" if there is Significant financial penalties may be associated with the improper no enclosure below the lowest floor other than insect design, construction, conversion, screening or open wood latticework. "Open" means that at or use of areas below the lowest least 50 percent of the lattice construction is open. floor. 2. A building is subject to a more expensive "with obstruction" rate if service equipment or utilities are located below the lowest floor or if breakaway walls enclose an area of less than 300 square feet below the lowest floor. 3. If the area below the lowest floor has more than 300 square feet enclosed by breakaway walls, has non-breakaway walls, or is finished, the floor of the enclosed area is the building's lowest floor and 7-16 COASTAL CONSTRUCTION MANUAL Volume II PRE-DESIGN CONSIDERATIONS 7 the insurance agent must submit more information on the structure to the NFIP before the policy's premium can be determined. Although the NFIP allows enclosures below the lowest floor, enclosures affect the flood insurance premiums. The addition of a floor system above the ground, but below the lowest floor of the living space, can result in additional impacts to flood insurance premiums. 7.6.1.2 Coverage The flood insurance that is available under the NFIP is called a Standard Flood Insurance Policy (SFIP). See FEMA F-122, NOTE National Flood Insurance Program Dwelling Form: Standard The amount of building and Flood Insurance Policy (FEMA 2009a) for more information contents coverage should be about NFIP coverage. based on replacement value, not market value. Replacement value To be insurable under the NFIP, a building must be walled is the actual cost of rebuilding and roofed with two or more rigid exterior walls and must the building or replacing the contents.This may be higher or be more than 50 percent above grade. Examples of structures lower than market value. that are not insurable because they do not meet this definition are gazebos, pavilions, docks, campers, underground storage tanks, swimming pools, fences, retaining walls, seawalls, bulkheads, septic tanks, and tents. Buildings constructed entirely over water or seaward of mean high tide after October 1, 1982, are not eligible for flood insurance coverage. Certain parts of boathouses located partially over water (e.g., ceiling, roof over the area where boats are floated) are not eligible for coverage. Coverage does not include contents. Contents of insurable walled and roofed buildings can be insured under separate coverage within the same policy. Finishing materials and contents in basements or in enclosures below the lowest elevated floor in post-FIRM buildings are not covered with some exceptions. Certain building components and contents in areas below the elevated floors of elevated buildings are covered. Coverage can even include some items prohibited by FEMA/local floodplain management regulations if the NFIP deems the items essential to the habitability of the building. Designers and building owners should not confuse insurability with proper design and construction. Moreover, significant financial penalties (e.g., increased flood insurance rates, increased uninsured losses) may result from improper design or use of enclosed areas below the BFE. With the above caveats in mind, buildings insured under the NFIP include coverage (up to specified policy limits) for the following items below the BFE: 72. Minimum-code-required utility connections, electrical outlets, switches, and circuit breaker boxes Footings, foundation, posts, pilings, piers, or other foundation walls and anchorage system(s) as required for the support of the building Drywall for walls and ceilings and nonflammable insulation (in basements only) E Stairways and staircases attached to the building that are not separated from the building by an elevated walkway COASTAL CONSTRUCTION MANUAL 7-17 11 7 PRE-DESIGN CONSIDERATIONS Volume II _- Elevators, dumbwaiters, and relevant equipment, except for such relevant equipment installed below the BFE on or after October 1, 1987 I-, Building and personal property items—necessary for the habitability of the building—connected to a power source and installed in their functioning location as long as building and personal property coverage has been purchased. Examples of building and personal property items are air conditioners, cisterns, fuel tanks, furnaces, hot water heaters, solar energy equipment,well water tanks and pumps, sump pumps, and clothes washers and dryers. • Debris removal for debris that is generated during a flood An SFIP does not provide coverage for the following building components and contents in areas below the elevated floors of elevated residential buildings: Breakaway walls and enclosures that do not provide support to the building • Drywall for walls and ceilings L Non-structural slabs beneath an elevated building [1 Walks, decks, driveways, and patios outside the.perimeter of the exterior walls of the building L Underground structures and equipment, including wells, septic tanks, and septic systems t- Equipment, machinery, appliances, and fixtures not deemed necessary for the habitability of the building Fences, retaining walls, seawalls, and revetments r. Indoor and outdoor swimming pools 1.7 Structures over water, including piers, docks, and boat houses t' Personal property L. Land and landscaping 7.6.1.3 Premiums Premiums are based on the seven rating factors discussed in Section 7.6.1.1, plus the following: An expense constant L: A Federal policy fee I-= The cost of Increased Cost of Compliance coverage E. The amount of deductible the insured chooses If a community elects to exceed the minimum NFIP requirements, it may apply for a classification under the NFIP Community Rating System (CRS). Based on its floodplain management program, the community 7-18 COASTAL CONSTRUCTION MANUAL Volume II PRE-DESIGN CONSIDERATIONS 7 could receive a CRS classification that providdyes up to a 45 percent premium discount for property owners within the community. At the time of this publication, nearly 1,250 communities were participating in the CRS, representing more than 69 percent of all flood insurance policies. For more information on the CRS, see Section 5.2.4. Tables 7-2, 7-3, and 7-4 list sample NFIP premiums for a post-FIRM, one-story, single-family residence without a basement located in various flood zones. For buildings in Zone V,premiums are somewhat higher for structures with breakaway obstructions, and premiums are dramatically higher for structures with obstructions (e.g., service equipment, utilities, non-breakaway walls) below the lowest floor. Reductions in flood insurance premiums can quickly offset the increased costs associated with building above the BFE. For buildings in Zone A, premiums are higher when proper flood openings are not provided in enclosed areas or when service equipment or utilities are located below the BFE. i Table 7-2.Sample NFIP Flood Insurance Premiums for Buildings in Zone A; $250,000 Building/$100,000 Contents Coverage Floor Elevation Reduction in Annual above BFE Annual Flood premium Savings Premium 0 0% $ 1,622 $0 1 foot • 45% $897 $725 ; 2 feet 61% $638 $984 3 feet : 66% $548 $ 1,074 4 feet 67% $530 $ 1,092 Rates as of May 2011 per the National Flood Insurance Program Flood Insurance Manual(FEMA 2011)for a Zone V structure free of obstruction. Rates include building($250,000),contents($100,000),and associated fees,including increased cost of compliance. Table 7-3. Sample NFIP Flood Insurance Premiums for Buildings in Zone V Free of Obstruction Below the Lowest Floor;$250,000 Building/$100,000 Contents Coverage Reduction in Floor Elevation Annual Flood Annual Savings above BFE premium Premium 0 0% $7,821 $ 0 =1 foot 33% $5,256 $2,565 2feet 55% $3,511 $4,310 ' - 3 feet 65% $2,764 $5,057 4 feet 71% $2,286 $5,535 Rates as of May 2011 per the National Flood Insurance Program Flood Insurance Manual(FEMA 2011)for a Zone V structure free of obstruction. Rates include building($250,000),contents($100,000),and associated fees,including increased cost of compliance;premium to be determined by NFIP underwriting. COASTAL CONSTRUCTION MANUAL 7-19 7 PRE-DESIGN CONSIDERATIONS Volume II Table 7-4.Sample NFIP Flood Insurance Premiums foriBuildings in Zone V with Obstruction Below the Lowest Floor;$250,000 Building/$100,000 Contents Coverage Floor Elevation Reduction in Annual above BFE Annual Flood premium Savings Premium 0 0% $ 10,071 $0 1 foot 22% $7,901 $2,170 2 feet 40% $ 6,056 $4,015 3 feet 50% $5,076 $i4,995 4 feet 54% $4,591 $:5,480 Rates as of May 2011 per the National Flood Insurance Program Flood Insurance Manual(FEMA 2011)for a Zone V structure free of obstruction. Rates include building($250,000),contents($100,000),and associated fees,including increased cost of compliance;premium to be determined by NFIP underwriting. 7.6.1.4 Designing to Achieve Lower Flood Insurance Premiums Tables 7-2,7-3, and 7-4 demonstrate that considerable savings can be achieved on flood insurance premiums by elevating a building above the BFE and by constructing it to be free of obstruction. Other siting, design and construction decisions can also lower'premiums. Designers should refer to FEMA's V Zone Risk Factor Rating Form to estimate flood insurance premium discounts and as a planning tool to use with building owners. The form is in Chapter 5 of the Flood Insurance Manual (FEMA 2011), available at http://www.fema.gov/business/nfip/manual.shtm. Discount points,which translate into reduced premiums, are awarded for: E Lowest floor elevation E' Siting and environmental considerations I C Building support systems and design details u Obstruction-free and enclosure construction considerations In addition to lowest floor elevation and free-of-obstruction discounts illustrated in Tables 7-2 and 7-3, flood insurance premium discounts also can be obtained for: C. Distance from shoreline to building rz Presence of large dune seaward of the building, Presence of certified erosion control device or ongoing beach nourishment project O Foundation design based on eroded grade elevation and local scour O-' Foundation design based on this Manual and ASCE 7-10 loads and load combinations i0 Minimizing foundation bracing - 7-20 � COASTAL CONSTRUCTION MANUAL Volume II PRE-DESIGN CONSIDERATIONS 7 r •- Spacing of piles/columns/piers h� Size and depth of piles and pier footings Superior connections between piles/columns/piers and girders Some poor practices reduce discount points.Negative discount points,which result in higher flood insurance premiums, are given for: E Shallow pile embedment E Certain methods of pile installation E Small-diameter piles or columns • Non-bolted connections between piles/columns/piers and girders r: Over-notching of wood piles L Small pier footings Presence of elevators, equipment, ductwork and obstructions below the BFE Presence of solid breakaway walls Presence of finished breakaway walls Table 10 (V Zone Risk Relativities) in the Flood Insurance Manual(FEMA 2011) provides an indication of how building discount points translate into flood premium discounts. Designers and owners should review this table and consult with a knowledgeable flood insurance agent regarding the flood insurance premium implications of using or avoiding certain design construction practices 7.6.2 Wind Insurance Wind insurance coverage is generally part of a homeowners insurance policy. At the time this Manual was published, underwriting associations (or "pools") provided last resort insurance to homeowners in coastal areas who could not obtain coverage from private companies. The following seven states had beach and windstorm insurance plans at the time this Manual was released:Alabama, Florida, Louisiana, Mississippi, North Carolina, South Carolina, and Texas. Georgia and New York provide this kind of coverage for windstorm and hail in certain coastal communities through other property pools. In addition, New Jersey operates the Windstorm Market Assistance Program (Wind-MAP) to help residents in coastal communities find homeowners insurance on the voluntary market. When Wind-MAP does not identify an insurance carrier for a homeowner, the New Jersey Insurance Underwriting Association, known as the FAIR Plan, may provide a policy for windstorm, hail, fire, and other perils but does not cover liability. Many insurance companies encourage their policyholders to retrofit their homes to resist wind-related damage, and some companies have established discount programs to reduce premiums, and other types of financial incentives, to reflect the risk reduction for homes that have been properly retrofitted. Some State insurance departments also have put in place insurance discount programs for properly retrofitted homes. The IBHS FORTIFIED for Existing Homes Program has been designed with the support of IBHS COASTAL CONSTRUCTION MANUAL 7-21 7 PRE-DESIGN CONSIDERATIONS Volume II member insurance companies, although each individual company makes its own decisions about how it is implemented. Wind is only one part of the rating system for multi-peril insurance policies such as a homeowners insurance policy. Most companies rely on the Homeowner's Multistate General Rules and State-specific exceptions Manual of the Insurance Services Office (ISO) as the benchmark for developing their own manuals. ISO stresses that the rules in the manual are advisory only and that each company decides what to use and charge. The ISO publishes a homeowner's manual in every state except Hawaii, North Carolina, and Washington (where State-mandated insurance bureaus operate). The seven basic factors in rating a homeowners insurance policy are: r` Form (determines type of coverage) t Age of the structure C1 Territory E Fire protection class C Building code effectiveness IT Construction type Protective devices The last five factors are discussed below. Premiums can also vary because of factors such as amount of coverage and deductible, but these additional factors are not related to building construction. Some companies, however, adjust their higher optional deductible credit according to construction type, giving more credit to more fire-resistant concrete and masonry buildings. 7.6.2.1 Territory Wind coverage credit varies by territory. An entire state may be one territory, but some states, such as Florida, are divided into county and sub-county territories. In Florida, the Intracoastal Waterway is often used as the boundary line. 7.6.2.2 Fire Protection Class ISO publishes a public protection classification for each municipality or fire district based on an analysis of the local fire department, water system, and fire alarm system. This classification does not affect wind coverage but is an important part of the rate. 7.6.2.3 Building Code Effectiveness Grading Schedule The adoption and enforcement of building codes by local jurisdictions are routinely assessed through the Building Code Effectiveness Grading Schedule (BCEGS) program, developed by the ISO. Participation in BCEGS is voluntary and may be declined by local governments if they do not wish to have their local 7-22 COASTAL CONSTRUCTION MANUAL 5 Volume II PRE-DESIGN CONSIDERATIONS 7 building codes evaluated.The results of BCEGS assessments are routinely provided to ISO's member private insurance companies, which in turn may offer rating credits for new buildings constructed in communities with strong BCEGS classifications. Conceptually, communities with well-enforced, up-to-date codes should experience fewer disaster-related losses and as a result, should have lower insurance rates. In conducting the assessment, ISO collects information related to personnel qualification and continuing education, as well as number of inspections performed per day. This type of information combined with local building codes is used to determine a grade for the jurisdiction. The grades range from 1 to 10, with a BCEGS grade of 1 representing exemplary commitment to building code enforcement, and a grade of 10 indicating less than minimum recognized protection. Most participating communities fall in the 3 to 5 grade range. 7.6.2.4 Construction Type To simplify insurance underwriting procedures, buildings are identified as being in only one of four categories: Frame: exterior walls of wood or other combustible construction, including stucco and aluminum siding L- Masonry veneer: exterior walls of combustible material, veneered with brick or stone G Masonry: exterior walls of masonry materials; floor and roof of combustible materials c) Superior: non-combustible, masonry non-combustible, or fire resistive Masonry veneer and masonry are often difficult to differentiate and are therefore often given the same rating. Not many single-family homes qualify for the superior category,which results in a 15 percent credit off rates for the masonry categories.A home in the superior category may also qualify for a wind credit because some insurers believe that buildings with walls, floors, and roofs made of concrete products offer good resistance to windstorms and Category 1 hurricanes. Therefore, a fire-resistive home may get a wind-resistive credit. ISO's dwelling insurance program allows companies to collect data from the owner, the local building department, or their own inspectors to determine whether a house can be classified as wind-resistive or semi-wind-resistive for premium credit purposes. 7.6.2.5 Protective Devices Protective devices are not considered basic factors but items that may deserve some credits. This approach is more common for fire and theft coverage than for wind. Fire and theft coverage credits sprinklers and fire and/or burglar alarms tied to the local fire or police stations. ISO's rules do not address wind-protective devices except in Florida. In Florida, a premium credit is given if exterior walls and roof openings (not including roof ridge and soffit vents) are fully protected with storm shutters of any style and material that are designed and properly installed to meet the latest ASCE 7-10 engineering standard. This standard has been adopted by Dade County. Shutters must be able to withstand impact from wind-borne debris in accordance COASTAL CONSTRUCTION MANUAL + 7-23 1 7 PRE-DESIGN CONSIDERATIONS Volume II with the standards set by the municipality, or if there are no local standards, by Dade County.The rules also provide specifications for alternatives to storm shuttaers, such as windstorm protective glazing material. 7.6.3 Earthquake Insurance Earthquake insurance is an addition to a regular homeowners insurance policy. Earthquake insurance carries a very high deductible—usually 10 or 15 percent of the value of the house. In most states, ISO has developed advisory earthquake loss costs based on a seismic model used to estimate potential damage to individual properties in the event of an earthquake. The model is based on seismic data, soil types, damage information from previous earthquakes, and structural analysis of various types of buildings. Based on this model, postal Zip codes have been assigned to rating bands and loss costs developed for each band. The number of bands varies within each state and, at times, within a county. In California, the California Earthquake Authority (CEA), a State-chartered insurance company, writes most earthquake policies for homeowners. These policies cover the dwelling and its contents and are subject to a 15-percent deductible. CEA rates are also based on a seismic model used to estimate potential damage to individual properties in the event of an earthquake. 7.7 Sustainable Design Considerations Sustainability concepts are increasingly being incorporated into residential building design and construction. The voluntary green building rating systems of the past decade are being replaced with adoption by local and State jurisdictions of mandatory minimum levels of compliance with rating systems such as the U.S. Green Building Council LEED for Homes Reference Guide (USGBC 2009) or consensus-based standards such as ICC 700-2008. These programs and standards use a system in which credits are accumulated as points assigned to favorable green building attributes pertaining to lot design, resource efficiency, energy efficiency, water efficiency, and indoor environmental quality. Although green building programs are implemerited as above-minimum building code practices, many aspects of green construction and its impact on structural performance and durability are not readily apparent upon initial consideration. Green building programs such as National Association of Home Builders (NAHB) Green, EarthAdvantage, and other State and local programs may incorporate LEED for Homes, ICC 700-2008, EnergyStar and other rating systems or product certifications as part of their offerings. For example, a homeowner may decide, to add a rooftop solar panel system after the home is built. Depending on its configuration, this system could act as a "sail" in high winds, adding significant uplift loads to the roof and possibly triggering localized structural failure. To maintain expected structural performance in a high-wind event, these additional loads not only must be accommodated by the roof framing, but the complete load path for these additional loads must be traced and connections or framing enhanced as needed. Examples of other green attributes that may require additional design consideration for resistance to natural hazards are large roof overhangs for shading (due to the potential for increased wind loads), vegetative green roofs (due to the presence of added weight and moisture to sustain the roof), and optimized or advanced framing systems that reduce overall material usage and construction waste (due to larger spacing between framing members and smaller header and framing member sizes). 7-24 COASTAL CONSTRUCTION MANUAL ti Volume II PRE-DESIGN CONSIDERATIONS 7 It is important to verify that the design wind speed for an area is not in excess of the recommended maximum wind speeds for these systems. Building for resilience should not work against other green practices by unreasonably increasing the material resources needed to construct the building. However, buildings constructed to survive natural hazards reduce the need to be rebuilt and thus provide a more sustainable design approach. When new green building attributes introduce new technology or new building materials into the building design, new interactions may affect the building's structural integrity and durability. Examples of interactions between green building attributes and resistance to natural hazards (e.g., resilience of the building) are described in FEMA P-798, Natural Hazard Sustainability of Residential Construction (FEMA 2010c). When implementing green attributes into a design, the designer should consider that building for resilience is possibly the most important green building practice. A green building fails to provide benefits associated with green building practices if it is more susceptible to heavy damage from natural hazard events that result in lost building function and increased cost of repair. 7.8 Inspection Considerations After the completion of building permits and construction plans, good inspection and enforcement procedures are crucial. For coastal construction, building inspectors, code officers, designers, and floodplain managers must understand the flood-resistant design and construction requirements for which they need to check. The earlier a deviation is found, the easier it is to take corrective action working with the homeowner and builder. A plan review and inspection checklist tailored to flood-related requirements should be used. Some of the inspections that can be performed to meet compliance directives with the local community's flood-resistant provisions are listed below. For a community that does not have a DFE, a BFE is applicable. L' Stake-out or site inspection to verify the location of a building; distances from the flood source or body of water can also be checked Ei Fill inspection to check compaction and final elevation when fills are allowed in SFHAs E Footing or foundation inspection to check for flood-opening specifics for closed foundations, lowest floor inspection for slab-on-grade buildings, and embedment depth and pile plumbness for pile- supported structures r: Lowest floor inspection (floodplain inspection) per Section 109.3.3 of 2012 IBC and Section R109.1.3 of 2012 IRC. This is also a good time to verify that the mechanical and electrical utilities are above the BFE or DFE for additional protection. . Final inspection points for flood-prone buildings can include: Enclosures below elevated buildings for placement of flood vents and construction of breakaway walls, where applicable Use of enclosures for consistency with the use in the permit Placement of exterior fill, where permitted, according to plans and specifications COASTAL CONSTRUCTION MANUAL 7-25 7 PRE-DESIGN CONSIDERATIONS Volume it Materials below the DFE for flood-resistance; see NFIP Technical Bulletin 2, Flood Damage-Resistant Materials Requirements (FEMA 2008) L: Building utilities to determine whether they have been elevated or, when instructions are provided, installed to resist flood damage Existence of as-built documentation of elevations If a plan review and inspection checklist have been used, verification that have been signed off and placed in the permit file with all other inspection documentation More information regarding inspections is available in FEMA P-762, Local Officials Guide for Coastal Construction (FEMA 2009b). 7.9 References ASCE (American Society of Civil Engineers). 2010r Minimum Design Loads for Buildings and Other Structures.ASCE Standard ASCE 7-10. ASCE. Flood Resistant Design and Construction. ASCE Standard ASCE 24. FEMA(Federal Emergency Management Agency). 2004.Answers to Questions about the National Flood Insurance Program. FEMA FIA-2. FEMA. 2008. Flood Damage-Resistant Materials Requirements. Technical Bulletin 2. FEMA. 2009a. National Flood Insurance Program Dwelling Form: Standard Flood Insurance Policy. FEMA F-122. FEMA. 2009b. Local Officials Guide for Coastal Construction. FEMA P-762. FEMA. 2010c. Natural Hazard Sustainability for Residential Construction. FEMA P-798. FEMA. 2011. Flood Insurance Manual.Available at http://www.fema.gov/business/nfip/manual.shtm. Accessed May 2011. IBHS (Insurance Institute for Business and Home Safety). 1999. Coastal Exposure and Community Protection:Hurricane Andrew's Legacy. Tampa. IBHS and Insurance Research Council. 2004. The Benefits of Modern Wind Resistant Building Codes on Hurricane Claim Frequency and Severity-A Summary Report. ICC (International Code Council). 2008. National Green Building Standard. ICC 700-2008. Country Club Hills, IL: ICC. ICC. 2011a. International Building Code(2012 IBC). Country Club Hills, IL: ICC. ICC. 2011b. International Residential Code for One-and Two-Family Dwellings(2012 IRC). Country Club Hills, IL: ICC. 7-26 COASTAL CONSTRUCTION MANUAL Volume II PRE-DESIGN CONSIDERATIONS 7 Mortgage Bankers Association. 2006. Natural Disaster Catastrophic Insurance The Commercial Real Estate Finance Perspective. Washington, D.C. Shows, E.W. 1978. "Florida's Setback Line—An Effort to Regulate Beachfront Development." Coastal Zone Management Journal 4(1,2): 151-164. USGBC (U.S. Green Building Council). 2009. LEED for Homes Reference Guide. • COASTAL CONSTRUCTION MANUAL 7-27 6 COASTAL CONSTRUCTION MANUAL -- : � "; In ' -r'rrrr-dm , Determining Si Loads _ _ _._ This chapter provides guidance on determining site-specific = loads from high winds, flooding, and seismic events. The CROSS REFERENCE loads determined in accordance with this guidance are applied For resources that augment the to the design of building elements described in Chapters 9 guidance and other information in through 15. this Manual, see the Residential Coastal Construction Web site The guidance is intended to illustrate important concepts (http://www.fema.gov/rebuild/ and best practices in accordance with building codes and mat/fema55.shtm). standards and does not represent an exhaustive collection of - — load calculation methods. Examples of problems are provided to illustrate the application of design load provisions of ASCE 7-10. For more detailed guidance, see the applicable building codes or standards. NOTE Figure 8-1 shows the process of determining site-specific All coastal residential loads for three natural hazards (flood, wind, and seismic buildings must be designed events). The process includes identifying the applicable and constructed to prevent flotation, collapse, and lateral building codes and standards for the selected site, identifying movement due to the effects building characteristics that affect loads, and determining of wind and water loads acting factored design loads using applicable load combinations. simultaneously. Model building codes and standards may not provide COASTAL CONSTRUCTION MANUAL I • 8 DETERMINING SITE-SPECIFIC LOADS Volume II load determination and design guidance for the'hazards that are listed in the figure. In such instances, supplemental guidance should be sought. The loads and load combinations used in this Manual are required by ASCE 7-10 unless otherwise noted. Although the design concepts that are presented in this Manual are applicable to both Allowable Stress Design (ASD) and Load and Resistance Factor Design (LRFD), all calculations, analyses, and load combinations are based on ASD. Extension of the design concepts presented in this Manual to the LRFD format can be achieved by modifying the calculations to use strength-level loads and resistances. Typical loads types and characteristics affecting loads for building design Dead and live loads —l— Site characteristics Flood 4 Building characteristics affecting loads affecting loads • Orientation in relation to flow • Hydrostatic • Height above grade • Buoyancy • Soil:erosion/scour potential • Obstructions below BFE• • Dune protection' Hydrodynamic • Foundation type/size • Building setback • • Breaking wave • Debris impact • Tsunami Site characteristics Wind Building characteristics affecting loads • Windward affecting loads •. Ground roughness.around • Leeward • Roof shape. site .. • Uplift • Building geometry • Debris potential . • Height above grade Acting on: • Main wind force resisting .• Number and location system,; of openings • Components and cladding I_ Other environmental loads • Snow • Rain I Site characteristics. - •. ,Seismic Building characteristics affecting loads . - • Base shear .,affecting loads • Soil: liquefaction. . •-1 • Building geometry • Depth of foundation ., - • Building weight ; members Factored design loads • Building system response • Soil:type of support material determined using coefficient . (e.g:, bedrock,clay) . appropriate • Height above grade', load combinations • Number of stories Figure 8-1. Summary of typical loads and characteristics affecting determination of design load 8-2 COASTAL CONSTRUCTION MANUAL { Volume II DETERMINING SITE-SPECIFIC LOADS 8 8.1 Dead Loads Dead load is defined in ASCE 7-10 as "... the weight of all materials of construction incorporated into the building including, but not limited to, walls, floors, roofs, ceilings, stairways, built-in partitions, finishes, cladding, and other similarly incorporated architectural and structural items, and fixed service equipment including the weight of cranes." The sum of the dead loads of all the individual elements equals the unoccupied weight of a building. The total weight of a building is usually determined by multiplying the unit weight of the various building materials—expressed in pounds per unit area—by the surface area of the materials. Unit weights of building elements, such as exterior walls, floors and roofs, are commonly used to simplify the calculation of building weight. Minimum design dead loads are contained in ASCE 7-10, Commentary. Additional information about material weights can be found in Architectural Graphic Standards (The American Institute of Architects 2007) and other similar texts. Determining the dead load is important for several reasons: c The dead load determines in part the required size of the foundation (e.g., footing width, pile embedment depth, number of piles). li Dead load counterbalances uplift forces from buoyancy when materials are below the stillwater depth (see Section 8.5.7) and from wind (see Example 8.9). L Dead load counterbalances wind and earthquake overturning moments. O Dead load changes the response of a building to impacts from floodborne debris and seismic forces. E Prescriptive design in the following code references and other code references is dependent on the dead load of the building. For example, wind uplift strap capacity, joist spans, and length of wall bracing required to resist seismic forces are dependent on dead load assumptions used to tabulate the prescriptive requirements in the following examples of codes and prescriptive standards: • 2012 IRC, International Residential Code for One-and Two-Family Dwellings (ICC 2011b) • 2012 IBC, International Building Code (ICC 2011a) • ICC 600-2008, Standard for Residential Construction in High-Wind Regions (ICC 2008) • WFCM-12, Wood Frame Construction Manual for One-and Two-Family Dwellings (AF&PA 2012) AISI S230-07, Standard for Cold formed Steel Framing prescriptive Method for One-and Two-family Dwellings(AISI 2007) 8.2 Live Loads Live loads are defined in ASCE 7-10 as "... loads produced by the use and occupancy of the building ... and do not include construction or environmental loads such as wind load, snow load, rain load, earthquake load, flood load, or dead load." Live loads are usually taken as a uniform load spread across the surface being designed. For residential one- and two-family buildings, the uniformly distributed live load for habitable areas (except sleeping and attic areas) in ASCE 7-10 is 40 pounds/square foot. For balconies and decks on COASTAL CONSTRUCTION MANUAL 8-3 II 8 DETERMINING SITE-SPECIFIC LOADS Volume II 0 one- and two-family buildings, live load IN j, , is 1.5 times the live load of the occupancy NOTE served but not to exceed 100 pounds/ square foot. This requirement typically The live loads in the 2012 IBC and 2012 IRC for . balconies and decks attached to one-and two-family translates to a live load of 60 pounds/ dwellings differ from those in ASCE 7-10. Under the square foot for a deck or balcony accessed 2012 IBC,the live load for balconies and decks is the from a living room or den, or a live load ' same as the occupancy served. Under the 2012 IRC, a of 45 pounds/square foot for a deck minimum 40 pounds/square foot live load is specified for balconies and decks. Strict adherence to the or balcony accessed from a bedroom. ASCE 7-10 live loads for a residential deck requires a ASCE 7-10 contains no requirements ' complete engineering design and does not permit use for supporting a concentrated load in a . of the prescriptive deck ledger table in the 2012 IRC residential building. . or the prescriptive provisions in AWC DCA6, which are based on a 40 pounds/square'foot live load. 8.3 Concept of Tributary or Effective Area and Application of Loads to a Building The tributary area of an element is the area of the floor, wall, roof, or other surface that , Rafter member \ . is supported by that element. The tributary area is generally a rectangle formed by one- \\. Tributary area half the distance to the adjacent element in \ �\ \ for wall stud each applicable direction. \\ I �� \ I. ! I The tributary area concept is used to �. I distribute loads to various building elements. \`\ ,� • I Figure 8-2 illustrates tributary areas for roof loads, lateral wall loads, and column - PI, or pile loads. The tributary area is a factor Tributary area Tributaryarea in calculating wind pressure coefficients, as for rafter member continues for length of rafter /op described in Examples 8.7 and 8.8. on both sides ' of ridge Wall stud �jVTributary area �, for center column `_AO.' )* �I Figure 8-2. 70 Examples of tributary _ areas for different Center column structural elements 8-4 COASTAL CONSTRUCTION MANUAL t i Volume II DETERMINING SITE-SPECIFIC LOADS 8 8.4 Snow Loads Snow loads are applied as a vertical load on the roof or other exposed surfaces such as porches or decks. Ground snow loads are normally specified by the local building code or building official. In the absence of local snow load information, ASCE 7-10 contains recommended snow loads shown on a map of the United States. When the flat roof snow load exceeds 30 pounds/square foot, a portion of the weight of snow is added to the building weight when the seismic force is determined. 8.5 Flood Loads Floodwaters can exert a variety of load types on building elements. Both hydrostatic and depth-limited breaking wave NOTE loads depend on flood depth. • Flood load calculation procedures cited in this Flood loads that must be considered in design include: Manual are conservative, given the uncertain conditions of a L-1 Hydrostatic load—buoyancy (flotation) effects, lateral severe coastal event. loads from standing water, slowly moving water, and • Background information and nonbreaking waves procedures for calculating coastal flood loads are ;; Breaking wave load presented in a number of publications, including Hydrodynamic load—from rapidly moving water, ASCE 7-10 and the Coastal including broken waves Engineering Manual(USACE 2008). r Debris impact load—from waterborne objects The effects of flood loads on buildings can be exacerbated by storm-induced erosion and localized scour and by long-term erosion, all of which can lower the ground surface around foundation elements and cause the loss of load-bearing capacity and loss of resistance to lateral and uplift loads. As discussed in Section 8.5.3, the lower the ground surface elevation, the deeper the water, and because the wave theory used in this Manual is based on depth-limited waves, deeper water creates larger waves and thus greater loads. 8.5.1 Design Flood TERMINOLOGY: In this Manual, "design flood" refers to the locally adopted FREEBOARD regulatory flood. If a community regulates to minimum NFIP requirements, the design flood is identical to the base flood Freeboard is additional height in(the 1-percent-annual-chance flood or 100-year flood). If a co into tai DFE to accouuntnt for or uncertainties in community has chosen to exceed minimum NFIP building determining flood elevations elevation requirements, the design flood can exceed the base and to provide a greater level of flood. The design flood is always equal to or greater than the flood protection. Freeboard may base flood. be required by State or local regulations or be desired by a property owner. COASTAL CONSTRUCTION MANUAL 8-5 8 DETERMINING SITE-SPECIFIC LOADS Volume II 8.5.2 Design Flood Elevation Many communities have chosen to exceed minimum NFIP building elevation requirements, usually by requiring freeboard above the base flood elevation (BFE) but sometimes by regulating to a more severe flood than the base flood. In this Manual, "design flood elevation" (DFE) refers to the locally adopted regulatory flood elevation. In ASCE 24-05, the DFE is defined as the "elevation of the design flood, including wave height, relative to the datum specified on the community's flood hazard map."The design flood is the"greater of the following two flood events: (1) the base flood, affecting those areas identified as SFHAs on the community's FIRM or (2) the flood corresponding to the area designated as a flood hazard area on a community's flood hazard map or otherwise legally designated." The DFE is,often taken as the BFE plus any freeboard required by a community, even if the community has not adopted a design flood more severe than the 100-year flood. Coastal floods can and do exceed BFEs shown on FIRMs and minimum required DFEs established by local and State governments. When there are differences between the minimum required DFE and the recommended elevation based on consideration of other sources, the designer, in consultation with the owner, must decide whether elevating above the DFE provides benefits relative to the added costs of elevating higher than the minimum requirement. For example, substantially higher elevations require more stairs to access the main floor and may require revised designs to meet the community's height restriction. Benefits include reduced flood damage, reduced'flood insurance premiums, and the ability to reoccupy homes faster than owners of homes constructed at the minimum allowable elevation. In both Hurricanes Katrina and Ike, high water marks after the storms indicated that if the building elevations had been set to the storm surge elevation, the buildings may have survived. See FEMA 549, Hurricane Katrina in the Gulf Coast(FEMA 2006), and FEMA P-757, Hurricane Ike in Texas and Louisiana (FEMA 2009), for more information. In addition to considering the DFE per community regulations, designers should consider the following before deciding on an appropriate lowest floor elevation: The 500-year flood elevation as specified in the Flood Insurance Study(FIS) or similar study. The 500-year flood elevation (including wave effects) represents a larger but less frequent event than the typical basis for the DFE (e.g., the 100-year event). In order to compare the DFE to the 500-year flood elevation, the designer must obtain the 500-year wave crest elevation from the FIS or convert the 500- year stillwater level to a wave crest elevation if the latter is not included in the FIS report. The elevation of the expected maximum storm surge as specified by hurricane evacuation maps. Storm surge evacuation maps provide a maximum storm surge elevation for various hurricane categories. Depending on location, maps may include all hurricane categories (1 to 5), or elevations for selected storm categories only. Most storm surge evacuation maps are prepared by the U.S.Army Corps of Engineers (USACE) and are usually available from the USAGE District Office or State/local emergency management agencies. Storm surge elevations are stillwater levels and do not include wave heights, so the designer must convert storm surge elevations to wave crest elevations. When storm surge evacuation maps are based on landmark boundaries (e.g., roads or other boundaries of convenience) rather than storm surge depths;the designer needs to obtain the surge elevations for a building site from the evacuation study(if available).The topographic map of the region may also provide 8-6 COASTAL CONSTRUCTION MANUAL 1 Volume II DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE 8.1. DESIGN STILLWATER FLOOD DEPTH CALCULATIONS (continued) elEQUATION A ds —(B E)( • Esw)—GS where: ds = design stillwater flood depth DFE = design flood elevation for a greater than 100-year flood event BFE = base flood elevation Esw, = design stillwater flood elevation in feet above datum (e.g. NGVD, NAVD) GS = lowest eroded ground elevation, in feet above datum, adjacent to building, excluding effects of localized scour around foundations Solution for Scenario #1: The design stillwater flood depth (ds) at seaward row of pilings using the 100-year stillwater elevation can be calculated using Equation 8.1 as follows: ds = Esw— GS ds = 10.1 ft NGVD—5.5 ft NGVD , di. = 4.6ft Note: This is the same solution that is calculated in Example 8.4, #3 Solution for Scenario #2: The design stillwater flood depth,(ds) at seaward row of pilings using the 100-year stillwater elevation and freeboard will be calculated just as in Scenario #1—freeboard should not be included in the.stillwater depth calculation but is used instead to raise the building to a higher- than-BFE level: ds = .Esw—GS ds = 10.1 ft NGVD—5.5 ft NGVD ds = 4.6ft Solution for Scenario #3: The design stillwater flood depth (ds) at seaward row of pilings using the 100-year stillwater elevation and the future conditions of sea-level rise and long-term erosion can be calculated as follows: Step 1: Increase 100-year stillwater elevation 50 years in the future to account for sea-level rise Esw= 10.1 ft NGVD + (0.01 ft/yr)(50 years) = 10.6 ft NGVD Step 2: Calculate the lowest ground elevation in ft above the datum adjacent to the seaward row of pilings in 50 years COASTAL CONSTRUCTION MANUAL 8-13 Volume II DETERMINING SITE-SPECIFIC LOADS 8 information about the storm surge depths'because the physical boundary elevation should establish the most landward extent of the storm surge. E Historical information and advisory flood elevations. Historical information showing flood levels and flood conditions during past flood events, if available, is an important consideration for comparison to the DFE. For areas subject to a recent coastal flood event, advisory flood elevations may be available based on the most recent flooding information unique to the site. Community FIRMs do not account for the effects of long-term erosion, subsidence, or sea level rise, all of which could be considered when establishing lowest floor elevations in excess of the DFE. Erosion can increase future flood hazards by removing dunes and lowering ground levels (allowing larger waves to reach a building site). Sea level rise can increase future flood hazards by allowing smaller and more frequently occurring storms to inundate coastal areas and by increasing storm surge elevations. Section 3.6 discusses the process a designer' could follow to determine whether a FIRM represents flood hazards associated with the site under present-day and future-based flood conditions. This section provides more information on translating erosion and sea level rise data into ds (design flood depth) calculations. Figure 8-3 illustrates a procedure that designers can follow to determine ds under a variety of future conditions. In essence, designers should determine the lowest expected ground elevation at the base of a building during its life and the highest expected stillwater elevation at the building during its life. Determine subsidence effects(if any)on the site • Obtain published subsidence rates • Multiply the subsidence rate by the building lifetime; lower ground elevations by this amount Determine the most landward expected shoreline location over the anticipated life of the building • Use published or calculated long-term erosion rate(feet/year), increasing the rate to account for errors and uncertainty. It is recommended that a minimum rate of 1.0 feet/year be used unless durable shore protection or erosion-resistant soil is present • Multiply the resulting erosion rate by the building lifetime(years)to compute the long-term erosion distance (feet). Use a minimum lifetime of 50 years • Measure landward(from the most landward historical shoreline)a distance equal to the long-term erosion distance.This will define the most landward expected shoreline Determine the lowest expected ground elevation at the base of the building or structure Beginning with the most landward expected;shoreline location: •calculate an eroded dune profile using a storm erosion model;or •calculate a stable bluff profile using available guidance and data - • Determine the highest expected stillwater elevation at the building •Obtain,published sea level rise rates for the site • Multiply sea level rise rate by the building lifetime; increase present SWEL by this amount Subtract future eroded ground elevation from future stillwater elevation to obtain design stillwater flood depth Figure 8-3. Flowchart for estimating maximum likely design stillwater flood depth at the site COASTAL CONSTRUCTION MANUAL 8-7 1 8 DETERMINING SITE-SPECIFIC LOADS Volume II The lowest expected ground elevation is detern fined by considering subsidence, long-term erosion, and erosion during the base flood. • Subsidence effects can be estimated by lowering all existing ground elevations at the site by the product of the subsidence rate and the building lifetime. For example, if subsidence occurs at a rate of 0.005 foot/year and the building lifetime is 50 years, the profile should be lowered 0.25 foot. • Figure 8-4 illustrates a simple way to estimate long-term effects on ground elevations at the building. Translate the beach and dune portion of the profile landward by an amount equal to the product of the long-term erosion rate and the building lifetime. If the erosion rate is 3 feet/year and the building lifetime is 50 years, shift the profile back 150 feet. ▪ Figure 8-4 also shows the next step in the process, which is to assess dune erosion (see Section 3.5.1) to determine whether the dune will be removed during a base flood event. o The lowest expected grade will be evident once the subsidence, long-term erosion, and dune erosion calculations are made. r The stillwater level is calculated by adding the expected sea level rise element to the base flood stillwater elevation. For example, if the FIS states the 100-year stillwater elevation is 12.2 feet NAVD, and if sea level is rising at 0.01 foot/year, and if the building lifetime is 50 years, the future conditions stillwater level will be 12.7 feet NAVD (12.2 + [(50)(0.01)]). f; The design stillwater flood depth, ds, is then calculated by subtracting the future conditions eroded grade elevation from the future conditions stillwater elevation. Figure 8-4. Erosion's effects 25 on ground 150 feet(3 feet/year x 50 years) elevationF41( I (Given:average annual 20— erosion rate=3 feet/year) C 15— Z - 100-year stillwater level m Lo. 10 0 cc 5 Today .. 50-year 0 ———— Post-storm -5 I I I I I I 0 100 200 300 400 500 600 700 800 Distance(feet) • • 8-8 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 8.5.3 Design Stillwater Flood Depth 1. NOTE In a general sense, flood depth can refer to two different depths The design stillwater flood depth (see Figure 8-5): (4) (including wave setup; see E Stillwater flood depth. The vertical distance between Section 8.5.4)should be used for calculating wave heights and the eroded ground elevation and the stillwater elevation flood loads. associated with the design flood. This depth is referred to as the design stillwater flood depth (ds). I, Design flood protection depth. The vertical distance between the eroded ground elevation and the DFE. This depth is referred to as the design flood protection depth (df,) but is not used extensively in this Manual. This Manual emphasizes the use of the DFE as the minimum elevation to which flood- resistant design and construction efforts should be directed. Determining the maximum design stillwater flood depth over the life of a building is the most important flood load calculation. Nearly every other coastal flood load parameter or calculation (e.g., hydrostatic load, design flood velocity, hydrodynamic load, design wave height, DFE, debris impact load, local scour depth) depends directly or indirectly on the design stillwater flood depth. Figure 8-5. Parameters that are BFE=Wave Crest Freeboard — determined or affected by r - flood depth dfr Hb t Wave Trough dJ G GS Erosion V d� design flood protection depth in feet BFE Base Flood Elevation in feet above datum Freeboard vertical distance in feet between BFE and DFE Hb breaking wave height=0.78d, (note that 70 percent of wave height lies above Env) d, design stillwater flood depth in feet G ground elevation, existing or pre-flood, in feet above datum Erosion loss of soil during design flood event in feet (not including effects of localized scour) GS lowest eroded ground elevation adjacent to building in feet above datum(including the effects of localized scour) COASTAL CONSTRUCTION MANUAL 8-9 8 DETERMINING SITE-SPECIFIC LOADS Volume II In this Manual, the design stillwater flood depth (ds) is defined as the difference between the design stillwater flood elevation (Esu,) and the lowest eroded ground surface elevation (GS) adjacent to the building (see Equation 8.1) where wave setup is included in the stillwater flood elevation. 6. --) EQUATION 8.1. DESIGN STILLWATER FLOOD DEPTH ds =Esw—GS (Eq. 8.1) where: 1;1 ds = design stillwater flood depth (ft) i Es. = design stillwater flood elevatiori in ft above datum (e.g., NGVD, NAVD) GS = lowest eroded ground elevation; in ft above datum, adjacent to a building, excluding effects of localized scour around the foundation Figure 8-5 illustrates the relationships among the various flood _ parameters that determine or are affected by flood depth. Note that in Figure 8-5 and Equation 8.1, GS is not the lowest existing pre- CROSS REFERENCE flood ground surface; it is the lowest ground surface that will result For a discussion of localized from long-term erosion and the amount of erosion expected to occur scour, see Section 8.5.10. during a design flood, excluding local scour effects. The process for __ determining GS is described in Section 3.6.4. Values for En, are not shown on FEMA FIRMs, but they are given in the FISs, which are produced in conjunction with the FIRM for communities. FISs are usually available from community officials and NFIP State Coordinating Agencies. Some states have made FISs available on their Web sites. Many FISs are also available on the FEMA Web site for free or are available for download for a small fee. For more information, go to http://www.msc.fema.gov. Design stillwater flood depth (ds) is determined using Equation A in Example 8.1 for scenarios in which a non-100-year frequency-based DFE is specified by the Authority Having Jurisdiction (AHJ). Freeboard tied to the 100-year flood should not be used to increase ds since load factors in ASCE 7 were developed for the 100-year nominal flood load. Example 8.1 demonstrates the calculation of the design stillwater flood depth for five scenarios.All solutions to example problems are in bold text in this Manual. 8-10 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 O,' J. r • - EXAMPLE.8.1. DESIGN STILLWAT ER FLOOD.DEPTH CALCULATIONS 1 Given: • Oceanfront building site.on landward side of a primary frontal dune (see Illustration A): • Topography along transect perpendicular to shoreline is shown in Illustration B; existing ground elevation at seaward row of pilings = 7.0 ft NGVD . • Soil is dense sand; no terminating tratum above—25 ft NGVD • Data from FIRM is as follows:flood hazard zone at site is Zone VE; BFE= 14.0 ft NGVD • °Data from FIS is as follows: 10-year stillwater elevation = 5.0 ft NGVD; 50-year Stillwater : elevation = 8.7.ft NGVD; 100-year stillwater elevation =.,10.1 ft NGVD;-500-year stillwater ' . elevation = 12:2 ft NGVD • 500-year wave crest elevation-_(DFE) specified by AHJ = 18.0 ft NGVD. - Local government requires 1.0 ft freeboard; therefore DFE=..14.0 ft NGVD (BFE)+ 1.0 ft= - 15.0.ft NGVD • Direction of wave and flow approach during design event is perpendicular to shoreline.. '. . ' •; The eroded ground elevation (basei flood conditions) at the seaward row of pilings;= , 5.5.ft NGVD ,„ Assume sea level_rise is 0.01 ft/yr ,' • Assume long-term average annual erosion rate is 2.0 ft/yr, no beach nourishment or shoreline stabilization, • Assume building life = 50 years iJ y6 2d,' I] Shoreline ! `, Site boundary,:,:" See Existing j dune crest I illustration i Building , B i footprint s It 1 I O {s ii ( Zone VET #��F, . , o i t (Elevation a I i 12 ft) � o I ; , ;, a a ,.__i _ �''. 7 Zone VE Zone VE Zone VE Zone VE } i (Elevation (Elevation , i (Elevation (Elevation 16 ft) 15 ft); . 1 1 14 ft) 13 ft) Illustration A. Plan.view of site and building location with flood hazard zones ... COASTAL CONSTRUCTION MANUAL 8-11 1 8 DETERMINING SITE-SPECIFIC LOADS Volume II ;I- EXAMPLE 8:1::DESIGN STILLWATER FLOOD DEPTH CALCULATIONS (continued) 40— Ground elevation at seaward pile before loss of dune Crest of primary 7.0 ft NGVD ' 30.= Dune reservoir frontal dune cross section 16.0 ft NGVD <1,100 ft2 Building • 20 100- ear stillwater elevation 1&0 Y ® ® ® 1-14.0 ft NGVD FE Z j 10.1 ft NGVD • 10 0 _ i. 7.. It 50 41 0 w �5 Toe of primary i ' ' s t, r, Heel of primary frontal dune frontal dune : _10— 4.1 ft NGVD Ground elevation ,: 6.0 ft NGVD Shoreline at seaward pile after 0.0 ft NGVD .Ground elevation loss of dune after loss of dune II 5.5 ft NGVD I( • I I I I I I I - I I I I. . I I I 0 20 ' 40 60 80 100• ,•120 140 160 180 200 220 : 240 260 : • Distance from shoreline(ft) Illustration B. Primary frontal dune will be lost to erosion during a 100-year floOd because dune reservoir is less than 1,100-ft2(Section A of Illustration A) Find: . . ' is 1 _ The design stillwater flood depth (ds) at the seaward row of piles:for: varying values-of stillwater elevation, presence of freeboard, and consideration of the effects of future conditions (e.g., sea-level 'rise and long-term erosion). The basis of the design flood for four scenarios are as.follows: 1. 100-year:stillwater elevation (NGVD). Future conditions riot.considered. 2. 100-year stillwater elevation (NGVD) plus freeboard. Future:conditions not considered. 3. 100-year stillwater elevation (NGVD). Future conditions (sea-level rise and long-term erosion)- :: in 50 years considered. 4. 500-year wave crest elevation (NGVD). Future conditions not considered. Note:Design stillwater flood depth (ds) is determined using Equation A for scenarios in which a non-100-: year frequency-based DFE is specified by the AHJ. Freeboard tied to the.100.year flood should not be used to increase ds since load factors=in ASCE 7 were leveloped for:the 1007 year nominal flood load. 8-12 COASTAL CONSTRUCTION MANUAL 1 8 DETERMINING SITE-SPECIFIC LOADS Volume II :EXAMPLE 8:1.:DESIGN STILLWATER FLOOD:DEPTH-CALCULATIONS (concluded) .;::. • In:50 years, the front toe of the dune will translate horizontally toward the building by (50 yr) (2 ft/yr) 100 ft landward is - �. ' : - : ' Taking into account the 1:50 (v:h) slope;of the eroded dune,the ground at the seaward row:of piles will drop (100,ft)(1/50)= 2 ft;over 50 years . . GS= 5:5 ft—2 ft..= 3.5 ft NGVD in i50 years F Step 3:Combine the effects of sea-level rise'and erosion to calculate ds : ' .. els .= .E—GS ds = 10.6ftNGVD-3.5ftNGVD 7:1ft; Solution.for Scenario#4: The design stillwater flood depth at seaward row_of pilings using teh gn 1? s p. g : AHJ's.500-year wave crest elevation (DFE) can be calculated using Equation A of Example 8 1:as i follows: : ..: DFE = di —( .BFE (ESA,)—GS , 'I 1 ds . (18 fC-)(10.1 ft) ft=13 Oft -;5.5ft=7.5-t 14ft : - = Note:Scenarios#1 through#4 show incremental' ncreases in the design stillwater flood depth ds, depending :on how conservative the designer wishes to be in selecting the design scenario.As the design stillwater flood : depth increases, the flood loads to-which the building foundation must be designed also increase. The , increase factor.listed in Table A-i.epresents: the square of the ratio of stillwater flood depth to the stillwater , flood depth from Scenario:#1(reference ease). '': 1. . Table A.Stillwater Flood Depths for Various Design;Scenarios and Approximate Load Increase Factor from :Increased.Values`of ds Scenario# Design d (ft) Approximate Load Condition s Increase Factor f — - --r — _ - - -- — —,I #1 (reference case) 100-year. .....,:i„...: 4.6 1, 1.0 �__ - - • ;I_ #2 ' 100 year:+freeboard - 4.6 - I- - -1.0 - - ". • : #3 'I 100- ear+future conditions 7.1 2.4 #4 'I50-year ' 7.5 2.7 ' _ j. i Note:In subsequent examples, the building in IllustrationsA and B and ds in Scenario#1 are used : ., , 8-14 COASTAL CONSTRUCTION MANUAL i Volume II DETERMINING SITE-SPECIFIC LOADS 8 8.5.4 Wave Setup Contribution to Mod Depth0.-001H NOTE Pre-1989 FIS reports and FIRMs do not usually include the effects of wave setup (dus), but some post-1989 FISs and Flood loads are applied to structures as follows: FIRMs do. Because the calculation of design wave heights and flood loads depends on an accurate determination of the total • Lateral hydrostatic loads— atstillwater flood depth, designers should review the effective stillwater two-thirds elevation depthnpoint of stillwater elevation FIS carefully, using the following procedure: • Breaking wave loads—at Check the hydrologic analyses section of the FIS for stillwater elevation mention of wave setup. Note the magnitude of the wave • Hydrodynamic loads—at setup. mid-depth point of stillwater elevation 1' Check the stillwater elevation table of the FIS for footnotes • Debris impact loads—at regarding wave setup. If wave setup is included in the stillwater elevation listed BFEs but not in the 100-year stillwater elevation, add wave setup before calculating the design stillwater flood depth, the design wave height, the design flood - velocity, flood loads, and localized scour.'If wave setup is TERMINOLOGY: already included in the 100-year stillwater elevation, use WAVE SETUP the 100-year stillwater elevation to determine the design - stillwater flood depth and other parameters. Wave setup Wave setup is an increase in should not be included in the 100-year stillwater elevation the stillwater surface near the shoreline due to the presence when calculating primary frontal dune erosion. of breaking waves. Wave setup typically adds 1.5 to 2.5 feet ter 8.5.5 Design BreakingWave Height to the lev tion nd should 9 flood elevation and should be discussed in the FIS. The design breaking wave height (Hb) at a coastal building site is one of the most important design parameters. Unless detailed analysis shows that natural or manmade obstructions will protect the site during a design event, wave heights at a site should be calculated as the heights of depth-limited breaking waves, which are equivalent to 0.78 times the design stillwater flood depth (see Figure 8-5). Note that 70 percent of the breaking wave height lies above the stillwater elevation. In some situations, such as steep ground slopes immediately seaward of a building, the breaking wave height can exceed 0.78 times the stillwater flood depth. In such instances, designers may wish to increase the breaking wave height used for design, with an upper limit for the breaking wave height equal to the stillwater flood depth. th 8.5.6 Design Flood Velocity --f WARNING Estimating design flood velocities (V) in coastal flood hazard areas is subject to considerable uncertainty. There is little This Manual does not provide reliable historical information concerning the velocity of guidance for estimating flood floodwaters duringcoastal flood events. The direction and issisvelocities higduhly cg mtsu ex The issue highly complex and site- velocity of floodwaters can vary significantly throughout a specific. Designers should look coastal flood event. Floodwaters can approach a site from one for model results from tsunami direction during the beginning of a flood event and then shift inundation or evacuation studies. COASTAL CONSTRUCTION MANUAL 8-15 8 DETERMINING SITE-SPECIFIC LOADS Volume II to another direction (or several directions). Floo4Taters can inundate low-lying coastal sites from both the front (e.g., ocean) and back (e.g., bay, sound, river). In a similar manner, flow velocities can vary from close to zero to high velocities during a single flood event. For these reasons, flood velocities should be estimated conservatively by assuming floodwaters can approach from the most critical direction relative to the site and by assuming flow velocities can be high (see Equation 8.2). EQUATION 8.2. DESIGN FLOOD VELOCITY Lower bound V= ds (Eq. 8.2a) Upper bound 'V=(gds)0'5 (Eq. 8.2b) where: V = design flood velocity (ft/sec) ds = design stillwater flood depth (ft) t = 1 sec ' g = gravitational constant (32.2 ft/sec2) For design purposes, flood velocities in coastal areas should be assumed to lie between V= (gds)0-5 (the expected upper bound) and V= ds/t(the expected lower bound). It is recommended that designers consider the following factors before deciding whether to use the upper-or lower-bound flood velocity for design: Flood zone D Topography and slope r. Distance from the source of flooding E Proximity to other buildings or obstructions The upper bound should be taken as the design flood velocity if the building site is near the flood source, in Zone V, in Zone AO adjacent to Zone V, in Zone A subject to velocity flow and wave action, on steeply sloping terrain, or adjacent to other large buildings or obstructions that will confine or redirect floodwaters and increase local flood velocities. The lower bound is a more appropriate design flood velocity if the site is distant from the flood source, in Zone A, on flat or gently sloping terrain, or unaffected by other buildings or obstructions. Figure 8-6 shows the velocity versus design stillwater flood depth relationship for non-tsunami, upper- and lower-bound velocities. Equation 8.2 shows the equations for the lower-bound and upper-bound velocity conditions. 8-16 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 i i Figure 8-6. Velocity(V)vs.design Stillwater.flood depth(d,) Velocity versus design 25— stillwater flood depth 20— •. • — • • c • • o .15— •.• d _ • .• • • • 1 — .' v 10 •' 5 Upper-bound velocity e Lower-bound velocity 6 - 0 I I I I- I I I I I I_' .I I I 'II I Iyy'I 'I I I I I I I I I: 1 2 3 . 4 5 6: 7 8 9 10 11 12 13 14 15 d,(feet) 8.5.7 Hydrostatic Loads Hydrostatic loads occur whenever floodwaters come into contact with a foundation, building, or building element. Hydrostatic loads can act laterally or vertically. Lateral hydrostatic forces are generally not;sufficient to cause deflection or displacement of a building or building element unless there is a substantial;difference in water elevation on opposite sides of the building or component. This is why the NFIP requires that openings be provided in vertical walls that form enclosures below the BFE for buildings constructed in Zone A (see Section 5.2.3.2). Likewise, vertical hydrostatic forces (buoyancy or flotation) are not generally a concern for properly constructed and elevated coastal buildings' founded on adequate foundations. However, buoyant forces can have a significant effect on inadequately elevated buildings on shallow foundations. Such buildings are vulnerable to uplift from flood and wind forces because the weight of a foundation or building element is much less when submerged than when not submerged. For example, one cubic foot of a footing constructed of normal weight concrete weighs approximately 150 pounds. But when submerged, each cubic foot of concrete displaces a cubic foot of saltwater,which weighs about 64 pounds/cubic foot.Thus,the foundation's submerged weight is only 86 pounds if submerged in saltwater (150 pounds/cubic foot — 64 pounds/cubic foot= 86 pounds/cubic foot), or 88 pounds if submerged in fresh water(150 pounds/cubic foot—62 pounds/ cubic foot = 88 pounds/cubic foot). A submerged footing contributes approximately 40 percent less uplift resistance during flood conditions. , Section 3.2.2 of ASCE 7-10 states that the full hydrostatic pressure of water must be applied to floors and foundations when applicable. Sections 2.33 and 2.4.2 of ASCE 7-10 require factored flood loads to be considered in the load combinations that model uplift and overturning design limit states. For ASD, flood loads are increased by a factor of 1.5 in Zone V and Coastal A Zones (and 0.75 in coastal flood zones with base flood wave heights less than 1.5 feet, and in non-coastal flood zones). These load factors are applied to COASTAL CONSTRUCTION MANUAL 8-17 8 DETERMINING SITE-SPECIFIC LOADS Volume II 4. account for uncertainty in establishing design flod intensity. As indicated in Equations 8-3 and 8-4 (per Figure 8-7), the design stillwater flood depth should be used when calculating hydrostatic loads. Any buoyant force (Fbuoy) on an object must be resisted by the weight of the object and any other opposing force (e.g., anchorage forces) resisting flotation. The'contents of underground storage tanks and the live load on floors should not be counted on to resist buoyant forces because the tanks may be empty or the building may be vacant when the flood occurs. Buoyant or flotation forces on a building can be of concern if the actual stillwater flood depth exceeds the design stillwater flood depth. Buoyant forces are also of concern for empty or partially empty aboveground tanks, underground tanks, and swimming pools. Lateral hydrostatic loads are given by Equation' 8.3 and illustrated in Figure 8-7. Note that fra (in Equation 8.3) is equivalent to the area of the pressure triangle and acts at a point equal to 2/3 ds below the water surface (see Figure 8-7). Figure 8-7 is presented here solely to illustrate the application of lateral hydrostatic force. In communities participating in the NFIP, local floodplain ordinances or laws require that buildings in Zone V be elevated above the BFE on an open foundation and that the foundation walls of buildings in Zone A be equipped with openings that allow floodwater to enter so that internal and external hydrostatic pressures will equalize (see Section 5.2) and not damage the structure. Vertical hydrostatic forces are given by Equation 8.4 and are illustrated by Figure 8-8. pi -W.) EQUATION 8.3. LATERAL HYDROSTATIC LOAD 1 z fta =2Ywds E ( q• 8.3a) where: f ra = hydrostatic force per unit width (lb/ft) resulting from flooding against vertical element Yw = specific weight of water (62.4 l i/ft3 for fresh water and 64.0 lb/ft3 for saltwater) ds = design stillwater flood depth (ft) Fsta=fta(w) (Eq. 8.3b) where: Fsta = total equivalent lateral hydrostatic force on a structure (lb) fta = hydrostatic force per unit width (lb/ft) resulting from flooding against vertical element w = width of vertical element (ft) 8-18 {' COASTAL CONSTRUCTION MANUAL II Volume II DETERMINING SITE-SPECIFIC LOADS 8 Figure 8-7. 1 Lateral flood force on a Vertical component vertical component Flood level t • No flooding 2/3d, Eroded j 4ground F surface NOTE F,„ hydrostatic force d, design stillwater flood depth 6 EQUATION 8:4. VERTICAL (BUOYANT) HYDROSTATIC FORCE Fbuoy =r (Vol) II (Eq. 8.4) where: i Fbuoy = vertical hydrostatic force (lb) resulting from the displacement of a given volume of floodwater yu, = specific weight of water (62.4 lb/ft3 for fresh water and 64.0 lb/ft3 for saltwater) Vol = volume of floodwater displaced by a submerged object (ft3) COASTAL CONSTRUCTION MANUAL 8-19 1 a DETERMINING SITE-SPECIFIC LOADS Volume II i Figure 8-8. Vertical (buoyant)flood1......1;1111 . .. _. _. _ force; buoyancy forces are drastically reduced for open foundations El El E Flood level (piles or piers) ' E] Ground n I_/A.J�.i, Continuous wall foundation J6. A--,A yr i t r � + 1g.;M i t '; AA*At � r �' i �. i � i �s t'' �. tf rrt-e1 f ,4 . . s. n ,{ :.., a.fr +:.{,;. r�': Yi�...f{`f F:, 1� ' :1: 3 IBuoya • • • ■ • • }.1 r' e .. t tiAF f � -; � ' nyw,�, t y t1. * -iti d-r - 4ft ��'ib% g 1 k (ti Ground tti i1;ft di -..f r . 1• .i.: p;,� .r r '`.. 2+ 4 +{ {ad' €', .4 s {�1 ii • • �• ri derground storage' . ' g r ,x•p a�,-, ` r:'-� i+ r +_f Y-4- -. T ,-i� }•i h aNT 4 i +,Y x 7 IL�1 k-f1 y, `Y' -44i:4.+ . L•: 'P, 1� b r 7 ' ^ i't i FY 1 , rk� , {c{`l If �: f d r f d ;Y � '1°~ `•v 14 j 1 : Underground structures can be affected by buoyancy when the soil below them becomes saturated. 8.5.8 Wave Loads Calculating wave loads requires the designer to .estimate expected wave heights, which, for the purposes of this Manual, are limited CROSS by water depths at the site of interest. These data can be estimated REFERENCE using a variety of models. FEMA uses its Wave Height Analysis for - - FFlood Insurance Studies (WHAFIS) model to estimate wave heights in calculatingr additional guidance v in wave loads, and wave crest elevations, and results from this model can be used see ASCE 7-10. directly by designers to calculate wave loads. Wave forces can be separated into four categories: r: From nonbreaking waves—can usually be computed as hydrostatic forces against walls and hydrodynamic forces against piles c: From breaking waves—short duration but large magnitude El From broken waves—similar to hydrodynamic forces caused by flowing or surging water 8-20 COASTAL CONSTRUCTION MANUAL , fI! Volume II DETERMINING SITE-SPECIFIC LOADS 8 - E Uplift—often caused by wave run-up, deflection, or 4 peaking against the underside of horizontal surfaces CROSS REFERENCE The forces from breaking waves are the highest and produce For more information about the most severe loads. It is therefore strongly recommended FEMA's WHAFIS model, see http://www.fema.gov/plan/ that the breaking wave load be used as the design wave load. prevent/fhm/dl_wfis4.shtm. The following three breaking wave loading conditions are of interest in residential design: L- Waves breaking on small-diameter vertical elements below the DFE (e.g., piles, columns in the foundation of a building in Zone V) Waves breaking against walls below the DFE (e.g., solid foundation walls in Zone A, breakaway walls in Zone V) Wave slam,where just the top of a wave strikes a vertical wall 8.5.8.1 Breaking Wave Loads on Vertical Piles The breaking wave load on a pile can be assumed to act at the stillwater elevation and is calculated using Equation 8.5. EQUATION 8.5. BREAKING WAVE)LOAD ON VERTICAL PILES 1 Fbrkp = 2 CdbYu,DHb2 q (E . 8.5) where: Fbrkp = drag force (lb) acting at the stillwater elevation Cdb = breaking wave drag coefficient (recommended values are 2.25 for square and rectangular piles and 1.75 for round piles) y,,, = specific weight of water (62.4 lb/ft3 for fresh water and 64.0 lb/ft3 for saltwater) D = pile diameter (ft) for a round pile or 1.4 times the width of the pile or column for a square pile (ft). Hb = breaking wave height (0.78 ds), in ft,where ds= design stillwater flood depth (ft) Wave loads produced by breaking waves are,greater than those produced by nonbreaking or broken waves. Example 8.3 shows the difference between the loads imposed on a vertical pile by nonbreaking waves and by breaking waves. COASTAL CONSTRUCTION MANUAL 8-21 8 DETERMINING SITE-SPECIFIC LOADS Volume II • 8.5.8.2 Breaking Wave Loads on Vertical Walls d NOTE Breaking wave loads on vertical walls are best calculated according to the procedure described in Criteria for Evaluating Equation 8.6 includes the Coastal Flood-Protection Structures (Walton et al. 1989). The hydrostatic component calculated using Equation 8.3. If Equation procedure is suitable for use in wave conditions typical during 8.6 is used, lateral hydrostatic coastal flood and storm events. The relationship for breaking force from Equation 8.3 should wave load per unit length of wall is shown in Equation 8.6. not be added to avoid double counting. EQUATION 8.6. BREAKING WAVE LOAD ON VERTICAL WALLS Case 1 (enclosed dry space behind wall): fbrkw =1.1Cpywds2 +2.4 y wds2 (Eq. 8.6a) Case 2 (equal stillwater elevation on both sides of wall): fbrkw =1.1Cp ywds2+1.9 ywds2 (Eq. 8.6b) where: fbrkw = total breaking wave load per unit length of wall (lb/ft) acting at the stillwater elevation Cp = dynamic pressure coefficient from Table 8-1 yw = specific weight of water (62.4 lb/ft3 for fresh water and 64.0 lb/ft3 for saltwater) ds = design stillwater flood depth (ft) Fbrkw =fbrkw(w) (Eq. 8.6c) where: Fbrkw = total breaking wave load (lb) acting at the stillwater elevation fbrkw = total breaking wave load per unit length of wall (lb/ft) acting at the stillwater elevation w = width of wall (ft) The procedure assumes that the vertical wall causes a reflected or standing wave to form against the seaward side of the wall and that the crest of the wave reaches a height of 1.2 ds above the stillwater elevation. The resulting dynamic, static, and total pressure distributions against the wall and resulting loads are as shown in Figure 8-9. 8-22 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 Table 8-1.Value of Dynamic Pressure Coefficient(Cp) as a Function of Probability of Exceedance Cp Building Type Probability of Exceedance Buildings and other structures that represent a low hazard to human life or 1.6 property in the event of failure 0.5 2.8 Coastal residential building 0.01 Buildings and other structures,the failure of which could pose a substantial 3.2 risk to human life 0.002 3.5 High-occupancy building or critical facility or those designated as essential 0.001 facilities Figure 8-9. Wall Breaking wave pressure Crest of reflected wave distribution against a A vertical wall 1.2d, Design Stillwater flood elevation(Eno) v Dynamic WEI Total force (acting at 0.1d,below E,,,,) d, Eroded ground elevation NOTE I d, design stillwater flood depth 1 E,,, design stillwater flood elevation above datum Equation 8.6 includes two cases: (1) a wave breaks against a vertical wall of an enclosed dry space, shown in Equation 8.6a, and (2) the stillwater elevation on both sides of the wall is equal, shown in Equation 8.6b. Case 1 is equivalent to a situation in which a wave breaks against an enclosure in which there is no floodwater inside the enclosure. Case 2,is equivalent to a situation in which a wave breaks against a breakaway wall or a wall equipped with openings that allow floodwaters to equalize on both sides of the wall. In both cases, waves are normally incident (i.e., wave crests are parallel to the wall). If breaking waves are obliquely incident (i.e., wave crests are not parallel to the wall; see Figure 8-10), the calculated loads would be lower. COASTAL CONSTRUCTION MANUAL 8-23 8 DETERMINING SITE-SPECIFIC LOADS Volume II Figure 8-10. IIff Wave crests not parallel Wall 4 NOTE: ,, to wall ,'; ,- BREAKAWAY WALLS , ,� When designing breakaway versus solid foundation walls using Equation � , , , 8.6,the designer should use a Cp of c ..- ,, , 1.0 rather than the C, of 1.6 shown ,� in Table 8-1. For more information on Wave LI breakaway walls, see Section 9.3. crests Wave crests not;! ;, parallel to wall _.� WARNING The likelihood of damage or loss can be reduced by installing louvered panels in solid walls or creating flood openings in breakaway walls for small flood depths, so that the panels do not break away under minor(nuisance)flood conditions. Figure 8-11 shows the relationship between water depth and wave height, and between water depth and breaking wave force, for the 1 percent and 50 percent exceedance interval events (Case 2). The Case 1 breaking wave force for these two events is approximately 1.1 times those shown for Case 2. r //,0\The breaking wave forces shown in Figure 8-11 are much higher than the typical wind forces that act on a coastal .' WARNING building,even wind pressures that occur during a hurricane or typhoon. However, the duration of the wave pressures Even waves less than 3 feet high can and loads is brief; peak pressures probably occur within 0.1 impose large loads on foundation + to 0.3 second after the wave breaks against the wall. See walls. Buildings in Coastal A Zones Wave Forces on Inclined and Vertical Wall Surfaces (ASCE should be designed and constructed to meet Zone V requirements(see 1995) for a discussion of breaking wave pressures and Section 6.5.2 in Chapter 6). durations. Post-storm damage inspections show that breaking wave /r+ loads have destroyed virtually all types of wood-frame walls and unreinforced masonry walls below the wave • ° WARNING crest elevation. Only highly engineered, massive structural _ elements are capable of withstanding breaking wave loads. Under the NFIP, construction of solid Damaging wave pressures and loads can be generated by foundation walls(such as those waves much lower than the 3-foot wave currently used by that the calculations of Figure 8-11 represent) is not permitted in Zone V FEMA to distinguish Zone A from Zone V. This fact was for new, substantially damaged, and confirmed by the results of FEMA-sponsored laboratory substantially improved buildings. tests of breakaway wall failures in which measured pressures 8-24 COASTAL CONSTRUCTION MANUAL 1 Volume II ;a DETERMINING SITE-SPECIFIC LOADS 8 •tt • . : Figure 8-11. 17 , _ _ , ,- , ... ._,. .,. t _I -- I 34,000 Water depth versus w 16-- Water depth vs.wave height ! - 32,000 wave height, and water 15 '----' Water depth vs.breaking / - • 30,000" ,° depth versus breaking ' • wave force-1 percent ill / wave force against, a 14-- exceedance(100-year event) 7 - 28,000 •o • vertical wall 13 -' ----- Water depth vs. breaking 26,000 -a,' wave force-50 percent 12 exceedance(2-year event) / !!0---24,000 a) 11 ._ /, ,= - 22,000 , a ,d 10 - -- �i' 20,000. .8 ... 9 - - f•-_L-- - 18,000 2 co 3 � - - •�•� ,'� i -- 14,000 411 / , 6- -- r- I �i- — - 12,000 I 4- i - it—,- -4 —— — 8,000 3 • 0 1 2 3 4 5 6 ! 7 8 9 10 . :Stillwater flood depth(feet) • on the order of hundreds of pounds/ square foot were generated by waves that were only 12 to 18 inches high. See Appendix H for the results of the tests. 8.5.8.3 Wave Slam The action of wave crests striking the elevated portion of a structure is known as "wave slam." Wave slam introduces lateral and vertical loads on the lower portions of the elevated structure (Figure 8-12).Wave slam force, which can be large, typically results in damaged floor systems (see Figure 3-26 in Chapter 3). This is one reason freeboard should be included in the design of coastal residential buildings. Lateral wave slam can be calculated using Equation 8.7, but vertical wave slam calculations are beyond the scope of this Manual. Equation 8.7 is similar to Equation 8.8 (hydrodynamic load) with the wave crest velocity set at the wave celerity (upper-bound flow velocity, given by Equation 8.2b) and a wave slam coefficient instead of a drag coefficient. The wave slam coefficient used in Equation 8.7 is an effective slam coefficient, estimated using information contained in Bea et al. (1999) and McConnell et al. (2004). Wave slam should not be computed for buildings that are elevated on solid foundation walls (the wave- load-on-wall calculation using Equation 8.6 includes wave slam) but should be computed for buildings that are elevated on piles or columns (wave loads on the piles or columns, and wave slam against the elevated building, can be computed separately and summed). COASTAL CONSTRUCTION MANUAL ; 8-25 i 8 DETERMINING SITE-SPECIFIC LOADS Volume II Figure 8-12. Lateral wave slam Bottom of lowest horizontal against an elevated structural member building h l—ll—Il—ldo Al'ii , —I l il—li�J' %- dJ I Wave f Eroded ground trough j. . elevation NOTE dr design stillwater flood depth h vertical;distance the wave crest extends above the bottom height of the lowest horizontal member --, EQUATION 8.7. LATERAL WAVE SLAM = F =f w 1 ywCsdshw (Eq. 8.7) 2 where: t Fs = lateral wave slam (1b) = lateral wave slam (lb/ft) CS = slam coefficient incorporating effects of slam duration and structure stiffness for typical residential structure (reommended value is 2.0) yw = unit weight of water (62.4 lb/ft3 for fresh water and 64.0 lb/ft3 for saltwater) cis = stillwater flood depth (ft) ;! h = vertical distance (ft) the wave crest extends above the bottom of the floor joist or floor beam w = length (ft) of the floor joist or floor beam struck by wave crest 8-26 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE 8.2. WAVE SLAM CALCULATION. Given: • Zone V building elevated on pile foundation near saltwater • Bottom of floor beam elevation = 15.0 ft NGVD • Length of beam (parallel to wave crest) = 50 ft • Design stillwater elevation = 12.0 ft NGVD • Eroded ground elevation = 5.0 ft NGVD • Cs(wave slam coefficient; see Equation 8.7) = 2.0 • yu„ = specific weight of water (62.4 lb/ft3 for fresh water and 64.0 lb/ft3 for saltwater) • A= (8 ft)(0.833 ft) = 6.664 ft2 Find:. 1. Wave crest elevation 2. Vertical height of the beam subject'to wave slam 3. Lateral wave slam acting on the elevated floor system Solution for#1: The wave crest elevation can be calculated as 1.55 times the stillwater depth, above the eroded ground elevation Wave crest elevation = 5.0 ft NGVD + 1.55 (12.0 ft NGVD—5.0 ft NGVD) = 15.9 ft NGVD Solution for#2: The vertical height of the beam subject to wave slam can be found as follows: Vertical height=wave crest elevation—bottom of beam elevation = 15.9 ft NGVD— 15.0ft NGVD = 0.9ft Solution for#3: Using Equation 8-7, the lateral wave slam acting on the elevated floor system can be found as follows: F =fsw= 2 yCsdshw=I 2' I(64 lb/ft3)(2.0)(7.0 ft)(0.9 ft)(50.ft)=20,160lb COASTAL CONSTRUCTION MANUAL 8-27 8 DETERMINING SITE-SPECIFIC LOADS Volume II 8.5.9 Hydrodynamic Loads As shown in Figure 8-13, water flowing around a building (or a structural element or other object) imposes loads on the building. In the figure, note that the lowest floor of the building is above the flood level and the loads imposed by flowing water affect only the foundation walls. However, open foundation systems, unlike that shown in Figure 8-13, can greatly reduce hydrodynamic loading. Hydrodynamic loads, which are a function of flow velocity and structural geometry, include frontal impact on the upstream face, drag along the sides, and suction on the downstream side. One of the most difficult steps in quantifying loads imposed by moving water is determining the expected flood velocity (see Section 8.5.6 for guidance on design flood velocities). In this Manual, the velocity of floodwater is assumed to be constant (i.e., steady-state flow). Hydrodynamic loads can be calculated using Equation 8.8. Elevating above the DFE provides additional protection from hydrodynamic loads for elevated enclosed areas. The drag coefficient used in Equation 8.8 is taken from the Shore Protection Manual, Volume 2 (USAGE 1984). Additional guidance is provided in Section 5.4.3 of ASCE 7-10 and in FEMA 259, Engineering Principles and Practices for Retrofitting Floodprone Residential Buildings (FEMA 2001). The drag coefficient is a function of the shape of the object around which flow is directed. When an object is something other than a round, square, or rectangular pile, the coefficient is determined by one of the following ratios (see Table 8-2): 1. The ratio of the width of the object (w) to the height of the object (h) if the object is completely immersed in water 2. The ratio of the width of the object (w) to the stillwater flood depth of the water (ds) if the object is not fully immersed Figure 8-13. Hydrodynamic loads on a Negative pressure building (suction)on downstream side Flood level _ _ _ Mpopp44 '‘41----III‘_ j ;tio 0 Frontal irnPa°t 1111%* Drag effect di iso on sides , Direction of flow —I NOTE ' d, design stillwater flood depth w width of building perpendicular to the direction of flow 8-28 COASTAL CONSTRUCTION MANUAL i Volume II DETERMINING SITE-SPECIFIC LOADS 8 EQUATION 8.8. HYDRODYNAMIC LOAD (FOR ALL FLOW VELOCITIES) 9 a _ 1 2A Fdyn 2 Cd pV (Eq. 8.8) • where: Fdyn = horizontal drag force (lb)acting at the stillwater mid-depth (half way between the stillwater elevation and the eroded ground surface) Cd = drag coefficient (recommended values are 2.0 for square or rectangular piles and 1.2 for round piles; for other;obstructions, see Table 8-2) p = mass density of fluid (1.94 slugs/ft3 for fresh water and 1.99 slugs/ft3 for saltwater) V = velocity of water(ft/sec); see Equation 8.2 A = surface area of obstruction normal to flow (ft2) = (w)(ds)(see Figure 8-13) or (w)(h)if the object is completely immersed Flow around a building or building element also Table 8-2. Drag Coefficients for Ratios of Width to creates flow-perpendicular forces (lift forces). When . Depth (w/ds)and Width to Height(w/h) a building element is rigid,lift forces can be,assumed Width-to-Depth Ratio Drag Coefficient to be small. When the element is not rigid, lift (w/ds or w/h) (Cd) forces can be greater'than drag forces. The equation ! 1-12 1.25 for lift force is the same as that for hydrodynamic 13-20 1.3 force except that the drag coefficient (Cd) is replaced with the lift coefficient (C1). In this Manual, the _-- --32. 1.4 foundations of coastal residential buildings are 33-40 1.5 considered rigid, and hydrodynamic lift forces can _' 41-80' 1.75 therefore be ignored. 81-120 1.8 Equation 8.8 provides the total force against a —__>120 _ -2.0 building of a given surface area, A. Dividing the total force by either length or width yields a force , ." per linear unit; dividing by surface area, A, yields 7 - a force per unit area. Example 8.3 shows the NOTE difference between the loads imposed on a vertical = pile by nonbreaking and breaking waves. As noted Lift coefficients(C1)are provided in Section 8.5.8, nonbreaking wave forces on piles in Introduction to Fluid Mechanics (Fox and McDonald 1985)and can be calculated as hydrodynamic forces. 1, in many other fluid mechanics textbooks. COASTAL CONSTRUCTION MANUAL 8-29 8 DETERMINING SITE-SPECIFIC LOADS Volume II `1„r EXAMPLE 8:3. HYDRODYNAMIC.LOAD ON PILES VERSUS BREAKING WAVE LOAD ON PILES Given: • • Building elevated on round-pile foundation near saltwater • Cd(drag coefficient for nonbreaking wave on round pile; see Equation 8.8) = 1.2 • Cdb (drag coefficient for breaking wave on round pile; see Equation 8.5) = 1.75 •- D'=.10 in. or 0.833 ft • dS= 8ft • Velocity ranges from 8 ft/sec to 16 ft/sec • p = mass density of fluid (1.94 slugs/ft3 for fresh water and 1.99 slugs/ft3 for saltwater) • • yw = specific weight of water (62.4 lb/ft3 for fresh water and 64.0 lb/ft3 for saltwater) • A = (8 ft)(0.833 ft) = 6.664 ft2 Find: 1 The range of loads from hydrodynamic flow around a pile 2. Load from a breaking wave on a pile • Solution for#1: The hydrodynamic load from flow past a pile is calculated using Equation 8.8 as follows: For a flood velocity of 8.ft/sec: 1 Fnonbrkp —2CdPV2A 1 • Fnonbrkp 2(1.2)(1,99 slugs/ft3)(8 ft/sec)2(6.664 ft2) Fnonbrkp= 509 lb/pile • For a flood velocity of 16 ft/sec: ' 1 2 Fnonbrkp — 2 CdPV A r1l Fnonbrkp =I 1 I(1.2)(1.99 slugs/ft3)(16 ft/sec)2(6.664.ft2) Fnonbrkp =2,037 lb/pile The range of loads froni a nonbreaking wave: 509 lb/pile to 2,037 lb/pile 8-30 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE 8.3. HYDRODYNAMIC LOAD ON PILES VERSUS BREAKING WAVE LOAD ON PILES (concluded) Solution for#2: The load from a breaking wave on a pile is calculated with Equation 8.5 as follows: ril ., Fbrkp = 2J(1.75)(64.0 lb/ft3)(0.833 ft)(0.78)(8 ft2) where: \: . Hb is the height of the breaking wave or (0.78)d, . FbrkP" 1,816 lb/pile '• Note: The load from the breaking wave is approximately 3.5 times the lower estimate of the hydrodynamic load. The upper estimate of the hydrodynamic load exceeds the breaking wave load only because of the very conservative nature of the,upper flood velocity estimate. 8.5.10 Debris Impact Loads Debris impact loads are imposed on a building by objects carried by moving water. The magnitude of these loads is very difficult to predict, but some reasonable allowance must be made for them. The loads are influenced by where the building is located in the potential debris stream, specifically if it is: E Immediately adjacent to or downstream from another building L= Downstream from large floatable objects:(e.g., exposed or minimally covered storage tanks) Among closely spaced buildings A familiar equation for calculating debris loads is given in ASCE 7-10, Commentary. This equation has been simplified into Equation 8.9 using Cstr, the values of which are based on assumptions appropriate for the typical coastal buildings that are covered in this Manual. The parameters in Equation 8.9 are discussed below. See Chapter C5 of ASCE 7-10 for a more detailed discussion of the parameters. Equation 8.9 contains the following uncertainties, each of which must be quantified before the effect of debris loading can be calculated: Li Size, shape, and weight (W) of the waterborne object �• Design flood velocity (V) r. Velocity of the waterborne object compared to the flood velocity Duration of the impact (At) (assumed to be equal to 0.03 seconds in the case of residential buildings is incorporated in Cs„, which is explained in more detail below) ri Portion of the building to be struck COASTAL CONSTRUCTION MANUAL 8=31 7 8 DETERMINING SITE-SPECIFIC LOADS g Volume II °11);. , EQUATION 8.9. DEBRIS IMPACT LOAD F =WVCDCBCS„ 1 (Eq. 8.9) where: Ft = impact force acting at the stillwater elevation (lb) W = weight of the object (lb) V = velocity of water (ft/sec), approximated by 1/2(gds)1i2 CD = depth coefficient (see Table 8-3) CB = blockage.coefficient (taken as 1.0 for no upstream screening, flow path greater than 30 ft; see below for more information) Cstr = Building structure coefficient (refer to the explanation of Cs„at the end of this section) = 0.2 for timber pile and masonry column supported structures 3 stories or less in height above grade = 0.4 for concrete pile or concrete or steel moment resisting frames 3 stories or less in height above grade = 0.8 for reinforced concrete foundation walls (including insulated concrete forms) Designers should consider locally adopted guidance because it may be based on more recent information than ASCE 7-10 or on information specific to the local hazards. Local guidance considerations may include the following: L= Size,shape,and weight of waterborne debris. The size, shape, and weight of waterborne debris may vary according to region. For example, the coasts of Washington, Oregon, and other areas may be subject to very large debris in the form of whole trees and logs along the shoreline. The southeastern coast of the United States may be more subject to debris impact from dune crossovers and destroyed buildings than other areas. In the absence of information about the nature of potential debris, a weight of 1,000 pounds is recommended as the value of W. Objects with this weight could include portions of damaged buildings, utility poles, portions of previously embedded piles, and empty storage tanks. ry Debris velocity. As noted in Section 8.5.6, flood velocity can be approximated within the range given by Equation 8.2. For calculating debris loads, the velocity of the waterborne object is assumed to be the same as the flood velocity.Although this assumption may be accurate for small objects, it may overstate debris velocities for large objects that drag on the bottom or that strike nearby structures. Portion of the building to be struck. The object is assumed to be at or near the water surface level when it strikes the building and is therefore assumed to strike the building at the stillwater elevation. E Depth coefficient. The depth coefficient (CD)t accounts for reduced debris velocity as water depth decreases. For buildings in Zone A with stillwater flood depths greater than 5 feet or for buildings in Zone V, the depth coefficient = 1.0. For other conditions, the depth coefficient varies, as shown in Table 8-3. 8-32 COASTAL CONSTRUCTION MANUAL 1 Volume II DETERMINING SITE-SPECIFIC LOADS 8 Table 8-3. Depth Coefficient(CD) by Flood pazard Zone and Water Depth Flood Hazard Zone and Water Depth CD Floodway(a)or Zone V 1.0 Zone A, stillwater flood depth > 5 ft 1.0 Zone A,stillwater flood depth=4 ft 0.75 Zone A,stillwater flood depth=2.5 ft 0.375 Zone A, stillwater flood depth < 1 ft 0.00 (a) Per ASCE 24-05,a"floodway"is a"channel and that portion of the floodplain reserved to convey the base flood without cumulatively increasing the water surface elevation more than a designated height." u Blockage coefficient. The blockage coefficient (CB) is used to account for the reduction in debris velocity expected to occur because of the screening provided by trees and other structures upstream from the structure or building on which the impact load is being calculated. The blockage coefficient varies, as shown in Table 8-4. Table 8-4.Values of Blockage Coefficient CB Degree of Screening or Sheltering within 100 Ft Upstream CB No upstream screening,flow path wider than 30 ft 1.0 , Limited upstream screening,flow path 20,-ft wide 0.6 Moderate upstream screening,flow path 10-ft wide 0.2 Dense upstream screening,flow path less than 5-ft wide 0.0 Building structure coefficient. The building structure coefficient, Cstr, is derived from Equation C5-3, Chapter C5,ASCE 7-10. Coefficient values for Cst,., (0.2, 0.4, and 0.8 as defined above for Equation 8.9) were generated by selecting input values recommended in ASCE 7-10, Chapter C5, with appropriate assumptions made to model typical coastal residential structures. The derived building structure coefficient formula with inputs is defined as follows: _ 3.14CIC0Rm. Cst' 2gAt where: CI = importance coefficient = 1.0 Co = orientation coefficient = 0.80 At = duration of impact = 0.03 sec g = gravitational constant (32.2 ft/sec2) RmQx = maximum response ratio assuming approximate natural period, T, of building types as follows: for timber pile and',masonry column, T= 0.75 sec; for concrete pile or concrete or steel moment resisting frames, T= 0.35 sec; and for reinforced concrete foundation walls, T= 0.2 sec. The ratio of impact duration (0.03 sec) to approximate natural period (T) is entered into Table C5-4 of ASCE 7-10 to yield the RmQx value. COASTAL CONSTRUCTION MANUAL 8-33 9 8 DETERMINING SITE-SPECIFIC LOADS Volume II 8.5.11 Localized Scour Waves and currents during coastal flood conditions create turbulence around foundation elements, causing localized scour around those elements. Determining potential scour is critical in designing coastal foundations to ensure that failure does not occur as a result of the loss in either bearing capacity or anchoring resistance around the posts, piles, piers, columns, footings, or walls. Localized scour determinations will require knowledge of the flood conditions, soil characteristics, and foundation type. At some locations, soil at or below the ground surface can be resistant to localized scour, and the scour depths calculated as described below would be excessive. When the designer believes the soil at a site may be scour-resistant, the assistance of a geotechnical;engineer should be sought before calculated scour depths are reduced. c Localized scour around vertical piles. Generally, localized scour calculation methods in coastal areas are based largely on laboratory tests and empirical evidence gathered after storms. The evidence suggests that the localized scour depth around a single pile or column or other thin vertical members is equal to approximately 1.0 to 1.5 times the pile diameter. In this Manual, a ratio of 2.0 is recommended (see Equation 8.10), consistent with the rule of thumb given in the Coastal Engineering Manual(USAGE 2008). Figure 8-14 illustrates localized scour at a pile,with and without a scour-resistant terminating stratum. Figure 8-14. Scour at single vertical E� foundation member,with 19--- and without underlying Flood elevation Pile Eroded ground surface scour-resistant stratum k....).— d Direction of flow Sm.,with terminating stratum e. . , 0.., -a.J o�®g,' n.��O< ®m omrs*�- m,� ` �a o o © o,-�o y v o%o . pi 7� 'r •or do ..waso - cdv® mc. ® o,o a.oG �o .�. 00., .+u ®cm . mv' mew © sca i' ^O- o � pGo-�; G7Z®9oa• c '5'm® o"ootmC Oo®Gac©aa <o. °-Q�o uGJo©Qs aC .3 o.Cif. ["ap . `�o . 0 p ®e-L c^ e wc , .co ® onc y, oc.5ood © g'nd0�1 , ob06 , n•:,aca ® naoo o�. 000 .o o®® Atli WIthOUto. pe°.�;e'o��,'oa 'oaTer imatingstratDm®o�a_te®a°mQo c0• 000ter,W:mamgstrausm cot�jS,aoGo;noneerodablesoiloabevrockyS — 7 e „ .,, perx.. ..o el v,a, c>a a C, imU 0� • e, �o-0 oo c+o ` ea mo 61 r.� .>D y ., 0 ®oecs er ,z10 ,yea ". 'o1e,-ay� .0,�o-.o `�• o` ©0, e ,, 0 o o 1 .s,,,p c,LStO oaQao,'�° ®�-od°, aors<o� , _ eu „ p . v ..,O oam..on� oammodF .oao Dooma ® „ccoo^ oncvo• a,' o oe< � y n°a7g'spci,' o°oxo eo°cAom<.'„o <- k <;a-4-4 owefa.% adoOo to©,,ol ,. ef NOTE a,s o- .c tt°o c on� o` 2,,%.t . n0o® 4od- b ,9®,f- Qba . ::�:oo ao:om oa©m 9®,eldO�daJ diameter flood depth : : e . o��® ;® 4,©� , o,,n,,, o`,oe,m 0..4 � ®oa j Smax localized maximum scour depth a®,o ®�e2-- d .�'O - %e . mo® aroovn ®0000'oao0: . , mom orlo�o c� �pa,-° od6 0 0 8-34 1 COASTAL CONSTRUCTION MANUAL a t 11 Volume II DETERMINING SITE-SPECIFIC LOADS 8 Or ' J EQUATION 8.10. LOCALIZED SCOUR AROUND A SINGLE VERTICAL PILE S =2.0a (Eq. 8.10) 1 where: Sm„ = maximum localized scour depth (ft) a = diameter of a round foundation element or the maximum diagonal cross-section dimension for a rectangular element 1 Observations after some hurricanes have shown cases in which localized scour around foundations far exceeded twice the diameter of any individual foundation pile. This was probably a result of flow and waves interacting with the group of foundation piles. In some cases,scour depressions were observed or reported to be 5 to 10 feet deep (see Figure 8-15).This phenomenon has been observed at foundations with or without slabs on grade but appears to be aggravated by the presence of the slabs. ',' Figure 8-15. :� Deep scour around �. -.- foundation piles, l ''' - - -- Hurricane Ike(Bolivar r -� _ : ; Peninsula,TX,2008) —did :1" ti rw .1+ �^ �F Pj:4 lir . 'LS- 1 J ..- .i, 7 1 I F -.70 P - - I I s R I Ilie. arm ak Some research on the interaction of waves and currents on pile groups suggests that the interaction is highly complex and depends on flow characteristics (depth,velocity, and direction),wave conditions (wave height,period, and direction), structural characteristics (pile diameter and spacing) and soil characteristics (Sumer et al. 2001). Conceptually, the resulting scour at a pile group can be represented as shown in Figure 8-16. In this Manual, the total scour depth under a pile group is estimated to be 3 times the single pile scour depth, plus an allowance for the presence of a slab or grade beam, as shown in Equation 8.11. The factor of 3 is consistent with data reported in the literature and post-hurricane observations. COASTAL CONSTRUCTION MANUAL 8-35 8 DETERMINING SITE-SPECIFIC LOADS Volume II Figure 8-16. Scour around a group of �a� foundation piles -+ SOURCE:ADAPTED FROM 1 SUMER ET AL.2001 SG-- -- t-- — Smax STOT — — — — -- — NOTE STOT total scour depth a pile diameter SG pile group scour Sma local scour depth (1)/ EQUATION 8.11. TOTAL LOCALIZED SCOUR AROUND VERTICAL PILES STOT =6a+2 ft (if grade beam and/or slab-on-grade present) (Eq. 8.l la) STOT =6a (if no grade beam or slab-on-grade present) (Eq. 8.11b) where: STOT = total localized scour depth (ft),; a = diameter of a round foundation element or the maximum diagonal cross-section dimension for a rectangular element 2ft = allowance for vertical scour due to presence of grade beam or slab-on-grade One difficulty for designers is determining whether local soils and coastal flood conditions will result in pile group scour according to Equation 8.11. Observations after Hurricanes Rita and Ike suggest that such scour is widespread along the Gulf of Mexico shoreline in eastern Texas and southwestern Louisiana, and observations after Hurricanes Opal and Ivan suggest that it occurs occasionally along the Gulf of Mexico shoreline in Alabama and Florida. Deep foundation scour has also been observed occasionally on North Carolina barrier islands (Hurricane Fran) and American Samoa (September 2009 tsunami). These observations suggest that some geographic areas are more susceptible than others, but deep foundation scour can occur at any location where there is a confluence of critical soil, flow, and wave conditions.Although these critical conditions cannot be identified precisely, designers should (1) be aware of the phenomenon, (2) investigate historical records for evidence of deep foundation scour around pile groups, and (3) design for such scour when the building site is low-lying, the soil type is predominantly silty, and the site is within several hundred feet of a shoreline. r Localized scour around vertical walls and enclosures. Localized scour around vertical walls and enclosed areas (e.g., typical Zone A construction) can be greater than that around single vertical piles, 8-36 ? COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 r u but it usually occurs at a corner or along one or two edges of the building (as opposed to under the entire building). See Figure 8-16. , Scour depths around vertical walls and enclosed areas should be calculated in accordance with Equation 8.12,which is derived from information in Coastal Engineering Manual(USAGE 2006). The equation is based on physical model tests conducted on large-diameter vertical piles exposed to waves and currents ("large" means round and square objects with diameters/side lengths corresponding to several tens of feet in the real world,which is comparable to the coastal residential buildings considered in this Manual). Equation 8.12, like Equation 8.11, has no explicit consideration of soil type, so designers must consider whether soils are highly erodible and plan accordingly. P EQUATION 8.12. TOTAL SCOUR DEPTH AROUND VERTICAL WALLS AND ENCLOSURES STOT =0.15L (Eq. 8.12) where: STOT = total scour depth (ft), maximum value is 10 ft L = horizontal length along the side of the building or obstruction exposed to flow and waves 8.5.12 Flood Load Combinations Designers should be aware that not all of the flood loads described in Section 8.5 act at certain locations or against certain building types. Table 8-5 provides guidance for calculating appropriate flood loads in Zone V and Coastal A Zones (flood load combinations for the portion of Zone A landward of the Limit of Moderate Wave Action [LiMWA] are shown for comparison). Table 8-5. Selection of Flood Loads for Fa in ASCE 7-10 Load Combinations for Global Forces Description Load Combination Greater of Fbrkp or Fdy„(on front row of piles only) Pile or open foundation in Zone V or Coastal A Zone + Fdy„(on all other piles)+F,(on one pile only) Solid (perimeter wall)foundation Greater of Fbrkw or Fay„+F,(in one corner) As discussed in Section 8.5.7, hydrostatic loads are included only when standing water will exert lateral or vertical loads on the building; these situations are usually limited to lateral forces being exerted on solid walls or buoyancy forces being exerted on floors and do not dominate in the Zone V or Coastal A Zone environment. Section 8.5.7 includes a discussion about how to include these hydrostatic flood loads in the ASCE 7-10 load combinations. COASTAL CONSTRUCTION MANUAL 8-37 8 DETERMINING SITE-SPECIFIC LOADS Volume II The guidance in ASCE 7-10, Sections 2.3 and 2.4 (Strength Design and Allowable Stress Design, respectively) also indicates which load combinations the flood load should be applied to. In the portion of Zone A landward of the LiMWA, the flood load Fa could either be hydrostatic or hydrodynamic loads. Both of these loads could be lateral loads; only hydrostatic will be a vertical load (buoyancy). When designing for global forces that will create overturning, sliding or uplift reactions, the designer should use Fa as the flood load that creates the most restrictive condition. In sliding and overturning, Fa should be determined by the type of expected flooding. Hydrostatic forces govern if the flooding is primarily standing water possibly saturating the ground surrounding a foundation; hydrodynamic forces govern if the flooding is primarily from moving water. When designing a building element such as a foundation, the designer should use Fa as the greatest of the flood forces that affect that element (Fsta or Fdp,) + Fz (impact loads on that element acting at the stillwater level).The combination of these loads must be used to develop the required resistance that must be provided by the building element. The designer should assume that breaking waves will affect foundation elements in both Zone V and Zone A. In determining total flood forces acting on the foundation at any given point during a flood event, it is generally unrealistic to assume that impact loads occur on all piles at the same time as breaking wave loads. Therefore, it is recommended that the load be calculated as a single wave impact load acting in combination with other sources of flood loads. For the design of foundations in Zone V or Coastal A Zone, load combination cases considered should include breaking wave loads alone, hydrodynamic loads alone, and the greater of hydrodynamic loads and breaking wave loads acting in combination with debris impact loads. The value of flood load, Fa, used in ASCE 7-10 load combinations, should be based on the greater of Fbrk or Fdy,,, as applicable for global forces (see Table 8-5) or F,+ (Fbrk or Fdp,), as applicable for an individual building element such as a pile. Example 8-4 is a summary of the information regarding flood loads and the effects of flooding on an example building. EXAMPLE 8.4. FLOOD LOAD EXAMPLE PROBLEM , .Given: •" Oceanfront building site on landward side of a primary frontal dune (see Example 8.1,.'- Illustration A) • •.Topography along transect perpendicular to shoreline is shown inExample 8.1, Illustration:B; existing ground elevation at seaward row of pilings = 7.0 ft NGVD • Soil is dense sand; no terminating stratum above—25 ft NGVD • Data from FIRM are as follows: flood hazard zone at site is Zone VE, BFE= 14.0 ft NGVD • Data from FIS are as follows: 100-year stillwater elevation = 10.1 ft NGVD, 10-year stillwater elevation = 5.0 ft NGVD 8-38 } COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE.8.4.FLOOD LOAD. EXAMPLE PROBLEM (continued) • Local government requires 1.0 ft freeboard; therefore DFE= 14.0 ft NGVD (BFE) + 1.0 ft= 15.0 ft NGVD • Building to be supported on 8-in. x 8-in. square piles, as shown in Illustration A' • Direction of wave and flow approach during design event is perpendicular to shoreline.(see Illustration A) . • The assumption is no grade beam or slab-on-grade present Find: 1. Primary frontal dune reservoir: determine whether dune will be lost or provide protection during design event 2. Eroded ground elevation beneath building resulting from storm erosion 3. Design flood depth (dd) at seaward row of piles . . 4. Probable range of design event flow velocities ' . 5.. Local scour depth (S)around seaward row of piles 6. Total localized scour (STbT) around piles 7. Design event breaking wave height (Hb) at seaward row of piles 8. Hydrodynamic (velocity flow)loads (Fdy„) on a pile (not in seaward row) . 9.. Breaking wave loads (Fork) on the seaward row of piles 10.Debris impact load (F;) from a 1,000-1b object acting on one pile Solution for#1: Whether the dune will'be lost or provides protection can be determined as follows: • The cross-sectional area of the frontal dune reservoir is above the 100-year stillwater elevation and seaward of the dune crest. . • The area (see Example 8.1, Illustration B) can be approximated as a triangle with the following area: A=gbh Where b is the base dimension,and h is the height dimension of the approximate triangle: =1(16 ft NGVD dune.crest elevation-10.1 ft NGVD 100-year stillwater elevation)(15 ft) 2 A = 44 ft2 but the area shown is slightly larger than that of the triangular area, so assume A = 50ft2 COASTAL CONSTRUCTION MANUAL 8-39 8 DETERMINING SITE-SPECIFIC LOADS Volume II • EXAMPLE 8.4: FLOOD LOAD EXAMPLEIPROBLEM (continued) • According to this Manual, the cross-sectional area of the frontal dune:reservoir must be at least 1,100 ft2:to survive a 100-year flood event. " .. . • 50 ft2 <1,100 ft2 and therefore, the dune will be lost and provide no protection during the 100-year event. Solution for#2: The eroded ground elevation beneath building can be found as"follows: • Remove dune from transect by drawing an upward-sloping (1:50 v:h) line landward from the : : lower of the dune toe or the intersection!of the 10-year stillwater elevation and the pre-storm: profile. • The dune toe is 4.1 ft NGVD. The intersection of the 10-year stillwater elevation and pre- storm profile is 5.0 ft NGVD. . •:.The dune toe is lower (4.1 ft NGVD < 5,:0 ft NGVD). Draw a line from the dune toe (located 75 ft from the shoreline at an elevation of 4.1 ft NGVD) sloping upward at a 1:50.(v:h) slope and find where the seaward'row of piles intersects. . this line. . Elevation.=4.1 ft NGVD+(145 ft 75 ft) — =5.5 1 ft NGVD - 50 Therefore, the eroded ground elevation at;the seaward row of pilings=5.5 ft NGVD Note: This value does not include local scour around the piles. Solution for#3: The design stillwater flood depth (ds) at seaward row of pilings can be calculated with Equation 8.1.as follows: • d5 =..E. -riv GS . Using the 100-year stillwater elevation (NGVD): ds 10.1 ft NGVD—5.5 ft NGVD ds. .= 4.6 ft Note:.This is the same solution as calculated in Example 8.1, Solution#1. Solution for#4: Use Equations 8.2a and 8.26,to determine the range of design flow velocities (V) as follows: ... . • Lower-bound velocity:. : . : . d I . .. V= V_ 4.6ft 1 sec 8-40 COASTAL CONSTRUCTION MANUAL 9 • Volume II DETERMINING SITE-SPECIFIC LOADS 8 al EXAMPLE 8.4. FLOOD LOAD EXAMPLE PROBLEM-(continued) Lower-bound V=4.6 ft/sec • Upper-bound velocity: V=(gds)°s Upper-bound V=(32.2 ft/sec2)(4.6 ft)o'S =12.2 ft/sec The range of velocities: 4.6 ft/sec to 12.2 ft/sec Note:t is assumed to be equal to 1 sec, as given in Equation 8.2. Solution for#5: Local scour depth (S) around seaward row of pilings can be found using Equation 8.10 as follows: S=2.0a where: a= V7.52 in.+7.52 in. _ 10.6 in. =0:88 ft 12 in./ft 12 in./f S=(2.0)(0.88 ft)=1.76 ft North—� Solution for_#6: To find the total localized scour (STOT) around piles, use � Equation 8.1lb as follows: 111 I STOT =6a=6(0.88 ft)=5.28 ft 60ft' u u u LI u L — A I . 3o 13j).-o 0 o C N Piles 7 CI CI a a C CO C7 ] 0 C . 1 Porch h_-- _ — — — --- - —_ — , e r r k 44ft ' >I-4—.16ft—).-1 Illustration A. Plan view of T Building elevation and plan . foundation view of pile foundation Flood flow direction . • COASTAL CONSTRUCTION MANUAL 8-41 8 DETERMINING SITE-SPECIFIC LOADS Volume II EXAMPLE 8.4. FLOOD LOAD EXAMPLE PROBLEM (continued) Solution for#7: Breaking wave height (Hb) at seaward row of pilings can be found as follows: At seaward row of pilings, Hb.= (ds)(0.78) where ds=4.6 ft from Solution#3 Hb =(4.6 ft)(0.78) 3.6 ft Solution for #8: Hydrodynamic (velocity flow). loads (Fdy„) on a pile (not in seaward row) can be calculated using Equation 8.8 as follows: On one pile: Fdyn = 2 CdpV 2A .. where: Cd = 2.0 for a square pile .. p. =. 1.99 slugs/ft3 8 in. ' . A = (10.1 ft—5.5 ft)=3.07 ftz 12 in. V = 12.2 ft/sec (because the building is on oceanfront, use the upper bound flow velocity for.calculating loads) Fdyn =2(2.0)(1.99)(12.2)2(3.07) Fdy„on one pile = 909 lb Solution for.#9: Breaking wave loads (Fb,.k ) on seaward row of pilings can be found using Equation 8.5 as follows: . . Fbrkp on one pile = 1,C DHb 2 2 dbYw where: . ' Cdb.=2.25 for square piles Yw=64.0 lb/ft3 for saltwater D.= 8 iti. (1.4)=0.93 ft 12 in. Hb =3.6 ft from Solution#7 - . Fbrkp. = 2(2.25)(64.01b/ft3)(0.93 ft)(3.6 ft)2 Fbrkp on one pile= 868 lb Fbrkp on seaward row of piles (i.e., 7 piles) (6251b)(7) = 6,076 lb 8-42 COASTAL CONSTRUCTION MANUAL Volume II j DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE 8.4. FLOOD LOAD EXAMPLE PROBLEM_(concluded) .. Solution for #10: Debris impact load (F;): from a 1,000-lb:'object on one pile can be determined using Equation 8:9 as follows:F =WV CDCBCst, • where: . : : W, = 1,000 lb CD = 1:0 CB = 1.0 Cstr =0.2 (timber pile):.. : " .. Debris impact load=(1,000 lb)(12.2 ft/sec)(1.0)(1.0)(0:2): : - Debris impact load=2,440.lb : Note: CD and_CB;are each assumed:o.be 1.0. " The following worksheets will facilitate flood load computations. • COASTAL CONSTRUCTION MANUAL 8-43 8 DETERMINING SITE—SPECIFIC LOADS a Volume II Worksheet 1. Flood Load Computation Non-Tsunami Cpastal A Zones(Solid Foundation) Flood Load Computation Worksheet: Non-Tsunami Coastal A Zones(Solid Foundation) OWNER'S NAME: PREPARED BY: ADDRESS: DATE: PROPERTY LOCATION: Constants Yw = specific weight of water = 62.4 lb/ft3 for fresh water and 64.0 lb/ft3 for saltwater p = mass density of fluid) = 1.94 slugs/ft3 for fresh water and 1.99 slugs/ft3 for saltwater g = gravitational constant= 32.2 ft/sec2 Variables ds = design stillwater flood depth (ft) Vol = volume of floodwater displaced (ft3) = V = velocity (fps) = Cdb = breaking wave drag coefficient = Hb = breaking wave height (ft) = C = dynamic pressure coefficient = Cs = slam coefficient = Cd = drag coefficient = w = width of element hit by water (ft),= h = vertical distance (ft) wave crest extends above bottom of member = A = area of structure face (ft2) = W = weight of object (lb) = CD = depth coefficient = CB = blockage coefficient = CStr = building structure coefficient = a = diameter of round foundation element = L = horizontal length alongside building exposed to waves (ft) Summary of Loads Fsta = Fbuoy = Fbrkw = Fs = Fdyn = FI = Smax = STOT = 8-44 COASTAL CONSTRUCTION MANUAL ti Volume II i DETERMINING SITE-SPECIFIC LOADS 8 9A Worksheet 1. Flood Load Computation Non-Tsunami Coastal A Zones(Solid Foundation)(concluded) Equation 8.3 Lateral Hydrostatic Load(Flood load on one side only) 1 2 Fa =2ywds w= Equation 8.4 Vertical (Buoyancy) Hydrostatic Load Fb„oy =yw(Vol)_ Equation 8.6 Breaking Wave Load on Vertical Walls Fbrkw =(1.1Cpywds2 +2.4ywds2)w (if dry behind wall) = or Fbrkw =(1.1Cp yw d?2 +1.9yw dr2)w (if stillwater elevation is the same on both sides of wall) = Equation 8.7 Wave Slam Fs =—ywCsdshw= Equation 8.8 Hydrodynamic Load _ Fdyn =-11 CdpV2A= Equation 8.9 Debris Load F =WVCDCBCsn = Equation 8.10 Localized Scour Around Single;Vertical Pile Smax= 2a= Equation 8.11 Total Localized Scour Around Vertical Piles STOT= 6a+2 ft (if grade beam and/or slab-on-grade present) = STOT= 6a (if no grade beam or slab-on-grade present) = Equation 8.12 Total Scour Depth Around Vertical Walls and Enclosures SMAx= 0.15L = COASTAL CONSTRUCTION MANUAL 8-45 8 DETERMINING SITE-SPECIFIC LOADS Volume II Worksheet 2. Flood Load Computation Non-Tsunamic Zone V and Coastal A Zone(Open Foundation) Flood Load Computation Worksheet: Non-Tsunami Zones V and Coastal A Zone(Open Foundation) OWNER'S,NAME: PREPARED BY: ADDRESS: DATE: PROPERTY LOCATION: Constants Yw = specific weight of water= 62.4 lb/ft3 for fresh water and 64.0 lb/ft3 for saltwater p = mass density of fluid = 1.94 slugs/ft3 for fresh water and 1.99 slugs/ft3 for saltwater g = gravitational constant= 32.2 ft/sec2 Variables ds = design stillwater flood depth (ft) = V = velocity(fps) = Cdb = breaking wave drag coefficient = a, D = pile diameter (ft) = Hb = breaking wave height (ft) = C = dynamic pressure coefficient = Cs = slam coefficient = Cd = drag coefficient for piles = w = width of element hit by water (ft) = h = vertical distance (ft) wave crest extends above bottom of member = W = debris object weight (lb) = CD = depth coefficient= CB = blockage coefficient = CStr = building structure coefficient = L = horizontal length alongside building exposed to waves (ft) = Summary of Loads Fbrkp = Fs = Fdy„ = F; = Smax = STOT = Equation 8.5 Breaking Wave Load on Vertical Piles 1 Fbrkp = 2 CdbYw DHb2 = 8-46 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 Worksheet 2. Flood Load Computation Non-Tsunamic Zone V and Coastal A Zone(Open Foundation)(concluded) Equation 8.7 Wave Slam Fs =- -y Csdshw— Equation 8.8 Hydrodynamic Load Fdyn =2 Car V A= Equation 8.9 Debris Load i F =WVCDCBCs„ = Equation 8.10 Localized Scour around.Single;Vertical Pile S,n = 2a= Equation 8.11 Total Localized Scour Around Vertical Piles STOT= 6a+ 2 ft (if grade beam and/or slab-on-grade present) _ STOT= 6a (if no grade beam or slab-on-grade present) = 8.6 Tsunami Loads In general, tsunami loads on residential buildings may be calculated in the same fashion as other flood loads; the physical processes are the same, but the scale of the flood loads is substantially different in that the wavelengths and runup elevations of tsunamis are much greater than those of waves caused by tropical and extratropical cyclones (see Section 3.2). If the tsunami acts as a rapidly rising tide, most of the damage is the result of buoyant and hydrostatic forces,.(see Tsunami Engineering[Caulfield 1980]). When the tsunami forms a bore-like wave, the effect is a surge of water to the shore and the expected flood velocities are substantially higher than in non-tsunami conditions. The tsunami velocities are very high and if realized at the greater water depths, would cause substantial damage to buildings in the path of the tsunami. Additional guidance on designing for tsunami forces including flow velocity, buoyant forces, hydrostatic forces, debris impact, and impulsive forces is provided in FEMA P646, Guidelines for Design of Structures for Vertical Evacuation from Tsunami (FEMA 2008b). For debris impact loads under tsunami conditions,see Section 6.5.6 of FEMA P646,which recommends an alternative to Equation 8.6 in this Manual for calculating tsunami debris impact loads. 8.7 Wind Loads ASCE 7-10 is the state-of-the-art wind load;design standard. It contains a discussion of the effects of wind pressure on a variety of building types and building elements. Design for wind loads is essentially the same whether the winds are due to hurricanes, thunderstorms, or tornadoes. Important factors that affect wind load design pressures include: D Location of the building site on wind speed maps COASTAL CONSTRUCTION MANUAL , 8-47 8 DETERMINING SITE-SPECIFIC LOADS Volume II fl Topographic effects (hills and escarpments),which create a wind speedup effect Building risk category(one-and two-family dwellings are assigned to Risk Category II; accessory structures may be assigned to Risk Category I) (see Section 6.2.1.1) n Building height and shape r: Building enclosure category: enclosed, partially enclosed or open L Terrain conditions, which determine building exposure category NOTE The effects of wind on buildings can be summarized as follows: Basic mapped wind speeds c Windward walls and windward surfaces of steep-sloped in ASCE 7-10 for Category II roofs are acted on by inward-acting, or positive pressures. structures (residential buildings) See Figure 8-17. are higher than those in ASCE 7-05 because they represent Leeward walls and leeward surfaces of steep-sloped roofs ultimate wind speeds or strength- and both windward and leeward surfaces of low-sloped factords designr wind SCE 7- are P factors for wind in ASCE 7-10 are roofs are acted on by outward-acting, or negative pressures. also different from those in ASCE ' See Figure 8-17. 7-05. In ASCE 7-10,the wind load factor in the load combinations c Air flow separates at sharp edges and at locations where the for LRFD strength design (LRFD) building geometry changes. is 1.0(but ASCE 7-05 provides a load factor of 1.6), and the L Localized suction, or negative, pressures at eaves, ridges, ASD wind load factor in the load combinations for allowable stress and the corners of roofs and walls are caused by turbulence design (ASD)for wind is 0.6(but and flow separation. These pressures affect loads on ASCE 7-05 provides a load factor components and cladding (C&C) and elements of the of 1.0). main wind force resisting system (MWFRS). _ . - __ The phenomena of localized high pressures occurring at locations where the building geometry changes is accounted for by the various pressure coefficients,in the equations for both MWFRS and C&C. Internal pressures must be included in the determination of net wind pressures and are additive to (or subtractive from) the external pressures. Openings and the natural porosity of building elements contribute to internal Enclosed building Partially enclosed building Wind ±I Is. ,4- 1� direction -II E' **I! _ Wind H II ± mil 441; ± direction 40. Figure 8-17. Effect of wind on an enclosed building and a building with an opening 8-48 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 I - pressure. The magnitude of internal pres'sures depends on whether the building is enclosed, partially enclosed, or open, TERMINOLOGY: as defined in ASCE 7-10. Figure 8-17 shows the effect of wind HURRICANE-PRONE _ on an enclosed and partially enclosed building. REGIONS In In wind-borne debris regions (as defined in ASCE 7-10), to the United Sta and it territories, hurricates ne-pronee areas in order for a building to be considered enclosed for design are defined by ASCE 7-10 as(1) purposes, glazing must either be impact-resistant or protected the U.S.Atlantic Ocean and Gulf with shutters or other devices that are impact-resistant. This of Mexico Coasts where the basic requirement also applies to glazing in doors. wind speed for Risk Category II buildings is greater than 115 Methods of protecting glazed openings are described in mph and (2) Hawaii, Puerto Rico, Guam, the Virgin Islands, and ASCE 7-10 and in Chapter 11 of this Manual. American Samoa. 8.7.1 Determining Wind Loads In this Manual, design wind pressures for MWFRS are based '* on the results of the envelope procedure for low-rise buildings. A low-rise building is defined in ASCE 7-10. The envelope FORMULA procedure in ASCE 7-10 is only one of several for determining MWFRS pressures in ASCE 7-10, but it is the procedure most A following formula oerts ASS CE 7-05 wind speedsds t to commonly used for designing low-rise residential buildings. ASCE 7-10 Risk Category II wind The envelope procedure for low-rise buildings is applicable for speeds. enclosed and partially enclosed buildings with a mean roof height (h) of less than or equal to 60 feet and where mean roof ASCE 7-10=(ASCE 7-05)( 1.6) height (h) does not exceed the smallest horizontal building dimension. For conversion from ASCE 7-10 to ASCE 7-05, use: Figure 8-18 depicts the distribution of external wall and roof ASCE 7-10 pressures and internal pressures from wind. The figure also ASCE 7-05= shows the mean roof height, which is defined in ASCE 7-10 1.6 Figure 8-18. Wind direction Distribution of roof,wall, and internal pressures on (-)External one-story, pile-supported building t o }y (+)InternalCO tti H� c *4-'S SSSSSSSSSS r* 2 r r Ground - COASTAL CONSTRUCTION MANUAL 8-49 8 DETERMINING SITE-SPECIFIC LOADS Volume II 1v1 U as "the average of the roof eave height and the height to the 1- highest point on the roof surface ..." Mean roof height is not NOTE the same as building height, which is the distal-ice from the ASCE 7-10 Commentary states ground to the highest point. that where a single component, sFor calculatingboth MWFRS and C&Cpressures, velocityan assemblageh as a roof truss, comprises an of structural pressures (q) should be calculated in accordance with Equation elements,the elements of 8.13. Velocity pressure varies depending on many factors that component should be including mapped wind speed at the site, height of the analyzed for loads based on C&C coefficients, and the single structure, local topographic effects, and surrounding terrain component should be analyzed •that affects the exposure coefficient. , for loads as part of the MWFRS. r.. _ . _ . - EQUATION 8.13. VELOCITY PRESSURE qZ =0.00256KZKzrKdV2 (Eq. 8.13) where: i qZ = velocity pressure evaluated at height z(psf) KZ = velocity pressure exposure coefficient evaluated at height z KZt = topographic factor Kd = wind directionality factor V = basic wind speed (mph) (3-sec gust speed at 33 ft above ground in Exposure Category C) The design wind pressure is calculated from the combination of external and internal pressures acting on a building element. This combination of pressures for both MWFRS and C&C loads in accordance with provisions of ASCE 7-10 is represented by Equation 8.14. 4011 .. . j EQUATION 8.14. DESIGN WIND PRESSURE FOR LOW-RISE BUILDINGS p=qh[GCpf—GCpi] (Eq. 8.14) where: p = design wind pressure qh = velocity pressure evaluated at mean roof height (h) (see Figure 8-18 for an illustration of mean roof height) GCp f = external pressure coefficient for C&C loads or MWFRS loads per the low-rise building provisions, as applicable GCp, = internal pressure coefficients based on exposure classification as applicable; GCpi for enclosed buildings is +/- 0.18 8-50 COASTAL CONSTRUCTION MANUAL i Volume II DETERMINING SITE-SPECIFIC LOADS 8 Figure 8-19 depicts how net suction pressures can vary across different portions of the building. Central portions of the walls represent the location of the least suction, while wall corners, the roof ridge, and the roof perimeter areas have potential for suction pressures that are 1.3, 1.4, and 2 times the central wall areas, respectively. Wall areas and roof areas that experience the largest suction pressures are shown as edge zones in Figure 8-19. The variation of pressures for different portions of the building is based on an enclosed structure (e.g., GCp;= +/- 0.18) and use of external pressure coefficients of the low-rise building provisions. Figure 8-19. Approximate maximum increases in Variation of maximum negative pressures based on location negative MWFRS 1.0xpressures based on ////' envelope procedures for 1.3x low-rise buildings �� 1.40x 1/////////4"i/," Ox ��oa�oo 00<$5 90° a�` $= Roof slope k Edgg Edge zone not less than 6 feet ypr1 To simplify design for wind, as well as establish consistency in the application of the wind design provisions of ASCE 7-10, several consensus standards with prescriptive designs tabulate maximum wind loads for the design of specific building elements based on wind pressures (both MWFRS and C&C are often referred to as "prescriptive" standards because they prescribe or tabulate load requirements for pressures) in accordance with ASCE 7-10. These standards, which are referenced in the 2012 IRC, are specific building applications based on factors such as wind speed, exposure, and height above grade. Examples of prescriptive standards for wind design that are referenced in the 2012 IRC are: rJ ICC 600-2008, Standard for Residential Construction in High-Wind Regions (ICC 2008) ANSI/AF&PA, Wood Frame Construction Manual(WFCM) (AF&PA 2012) ANSI/AISI-S230, Standard for Cold-Formed Steel Framing-Prescriptive Method for One and Two Family Dwellings(AISI 2007) Tabulated wind load requirements in these standards often use conservative assumptions for sizing members and connections. Therefore, load requirements are often more conservative than those developed by direct application of ASCE 7-10 pressures when design loads can be calculated for each element's unique characteristics. COASTAL CONSTRUCTION MANUAL 8-51 3 8 DETERMINING SITE-SPECIFIC LOADS Volume II 8.7.2 Main Wind Force Resisting Systern The MWFRS consists of the foundation; floor supports (e.g.,joists, beams); columns; roof rafters or trusses; and bracing, walls, and diaphragms that assist in transferring loads. ASCE 7-10 defines the MWFRS as "... an assemblage of structural elements assigned to provide support and stability for the overall structure. The system generally receives wind load from more than one surface." Individual MWFRS elements of shear walls and roof diaphragms (studs and cords) may also act as components and should also be analyzed under the loading requirements of C&C. For a typical building configuration with a gable roof, the wind direction is perpendicular to the roof ridge for two cases and parallel to the ridge in the other two cases. A complete analysis of the MWFRS includes determining windward and leeward wall pressures, side wall pressures, and windward and leeward roof pressures for wind coming from each of four principal directions. Figure 8-18 depicts pressures acting on the building structure for wind in one direction only. The effect of the combination of pressures on the resulting member and connection forces is of primary interest to the designer.As a result, for each direction of wind loading, structural calculations are required to determine the maximum design forces for members and connections of the building structure. Prescriptive standards can be used to simplify the calculation of MWFRS design loads. Examples of prescriptive MWFRS design load tables derived from the application of ASCE 7-10 wind load provisions are included in this Manual for the purpose of illustration, as follows: IT Roof uplift connector loads (see Table 8-6). The application of ASCE 7-10 provisions and typical assumptions used to derive the tabulated load values are addressed in Example 8.5. Equation 8.13 for velocity pressure and Equation 8.14 for determining design wind pressure are used to arrive at the design uplift connector load. The roof uplift connection size is based on moment balance of forces acting on both the windward and leeward side of the roof. The uplift load is used to size individual connectors and also provides the distributed wind uplift load acting at the buildings perimeter walls. Note that while wind speeds are based on 700-year Mean Recurrence Interval, the resulting uplift loads are based on ASD design. Diaphragm loads due to wind acting perpendicular to the ridge (see Table 8-7).Application of the ASCE 7-10 provisions and typical assumptions used to derive the tabulated load values are addressed in Example 8.6. The diaphragm load is based on wind pressures simultaneously acting on both the windward and leeward side of the building. The diaphragm load is used to size the diaphragm for resistance to wind and is also used for estimating total lateral forces for a given wind direction based on combining diaphragm loads for the roof and wall(s) as applicable. Total lateral forces from wind for a given direction can be used for preliminary sizing of the foundation and for determining shear wall capacity requirements. The example loads in Table 8-6 and Table 8-7, which are based on ASCE 7-10 envelope procedures for low- rise buildings, are used in Examples 8.7 and 8.8 to illustrate their application in the wind design of select load path elements. Tables 8-6 and 8-7 and Examples 8.5 and 8.6 are derived from wind load procedures in the WFCM (AF&PA 2012). Tables 8-6 and 8-7 are not intended to replace requirements of the building code or applicable reference standards for the actual design of a building to resist wind. 8-52 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 Table 8-6. Roof Uplift Connector Loads (Based bn ASD Design) at Building Edge Zones, plf(33-ft mean roof height, Exposure C) Wind Speed(a)(mph) - 110 115 120 130 140 150 160 170 180 Roof Span(ft) Roof uplift connector load(b)(c)(d)(plf) 24 189 215 241 298 358 424 494 568 647 32 237 269 303 374 451 534 622 716 816 40 285 324 364 450 544 643 750 864 985 48 333 379 426 527 636 753 879 1,012 1,154 • (a) 700-year wind speed,3-sec gust. Wind (b) Uplift connector loads are based on 33-ft mean roof height,Exposure C,roof dead load of 10 psf,and roof overhang length of 2 ft(see Example 8.5). Uplift\\ (c) Uplift connector loads are tabulated in pounds per linear ft of wall. Individual connector loads connector 's can be calculated for various spacing of connectors(e.g.,for spacing of connectors at 2 ft =,`. o.c.,the individual connector load would be 2 ft times the tabulated value). 11 Roof (d) Tabulated uplift connector loads are conservatively based on a 20-degree roof slope. span Reduced uplift forces may be calculated for greater roof slopes. Table 8-7. Lateral Diaphragm Load from Wind Perpendicular to Ridge, plf(33-ft mean roof height, Exposure C) Wind Speed(a)(mph) 110 115 120 130 140 150 160 170 180 Roof Span(ft) Roof diaphragm load(b)(c)for 7:12 roof slope(plf) 24 138 151 164 192 223 256 291 329 369 32 161 176 191 224 260 299 340 384 430 40 186 203 221 259 301 345 393 443 497 48 210 230 250 294 341 391 445 503 563 • Floor diaphragm load (plf) Any 154 168 183 214 249 286 325 367 411 Legend (a) 700-year wind speed,3-sec gust. n Tributary area for roof (b) Lateral diaphragm loads are based on 33-ft mean roof height,Exposure C,and wall diaphram height of 8 ft(see Example 8.6).Tabulated roof diaphragm loads are for a 7:12 roof slope. Larger loads can be calculated for steeper roof slopes and smaller loads can 0 Tributary area for floor diaphram be calculated for shallower roof slopes. (c) Total shear load equals the tabulated unit lateral load by the building length perpendicular to the wind direction. Wind direction Same figure as Example 8.6, Illustration A COASTAL CONSTRUCTION MANUAL 8-53 8 DETERMINING SITE-SPECIFIC LOADS Volume II • ga .EXAMPLE 8.5..ROOF UPLIFT CONNECTOR LOADS . . Given: • Roof span of 24 ft with 2-ft overhangs •. Roof/ceiling dead load of 10 psf • Wind load based on 150 mph, Exposure C at 33-ft mean roof height , • Building is enclosed • Kz.= 1.0:(velocity pressure exposure coefficient evaluated at height of 33 ft) • K2 = 1.0 (topographic factor) • Kd.= 0.85 (wind directionality) 6 psf dead load Wind direction Ida 9k IklOP *4 3 S 6 y1�p y 44Sf **1* Windward Leeward wall wall 2 ft < '24 ft > 2 ft f - r r Illustration A. Roof-to-wall uplift connection loads from wind forces Find: The roof-to-wall uplift connection load using the envelope procedure for low-rise buildings (see Figure 28.4-1 in ASCE 7-10). Solution: The roof-to-wall uplift connection load can be found using the envelope procedure for low- rise buildings as follows: • The velocity pressure (q).for the site conditions is determined from Equation 8.13 as follows: qh 0.00256KzKZtKdV2 qh:=0.00256(1.0)(1.0)(0.85)(150 mph)2.. qh =48.96 psf 8-54 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE 8.5. ROOF UPLIFT CONNECTOR LOADS (continued) • For ASD, multiply by the ASD wind load factor of 0.6,which comes from Load Combination 7 (See Section.8.10) ,0.6D + 0.6W ' qh =48.96 psf(0.6)=29.38 psf The largest uplift forces occur for a roof slope of 20 degrees where wind is perpendicular to the ridge.The addition of an overhang also increases the roof-to-wall uplift connection load. For the windward overhang, a pressure coefficient of 0.68 is used based on the gust factor of 0.85 and pressure coefficient of 0.80 from ASCE 7-10. Otherwise, pressure coefficients for other elements of the roof are based on GCp,= 0.18 and GCpf from the edge zone coefficients shown in Figure 28.4-1 of ASCE 7-10. Pressures and moments given below contain subscripts for their location: • W=windward • • L = leeward • • 0= overhang • R= roof . The design wind pressure is determined from Equation 8.14 as follows: p=qh(GCp f—GC pi) pwo =29.38 psf(-1.07.—0.68)=-51.4 psf pwR =29.38 psf(-1.07—0.18)=-36.7 psf PLR =29.38 psf(-0.69—0.18)=—25.6 psf PLO =29.38 psf(-0.69—0.18)=-25.6 psf • • The roof/ceiling dead load is adjusted for the load case where dead load is used to resist uplift forces as follows:. Dead load=10 psf(0.6)=6.psf where 0.6 is the ASD load factor for dead load in the applicable load combination.. • Wind loads on the roof have both a horizontal and vertical component. The uplift connector force, located at the windward wall, can be determined by summing moments about the leeward roof-to-wall connection and solving for the connector force that will maintain . .. moment equilibrium. Clockwise moments are considered positive. Moment (M) created by windward overhang pressures is solved as follows: Vertical component, windward overhang (VWO): COASTAL CONSTRUCTION MANUAL 8-55 8 DETERMINING SITE-SPECIFIC LOADS Volume II EXAMPLE 8.5. ROOF UPLIFT CONNECTOR LOADS (continued) Myivo =[(51.4 psf cos(20)] 2 ft +(-6 psf)(2 ft)](1 ft+24 ft)=2,270 ft-lb cos(20)) Horizontal component,windward overhang(HWO): M 0 =[-51.4 psf sin(20)] 2 ft 6 ft-lb cos(20)J _2tan(2o)Ji3 (' . 2 Moment (M) created by windward roof pressures is solved as follows: Vertical component, windward roof(VWR): . 12 ft MywR =[(36:7 psf cos(20)] J+(_6 psf)(12 ft)](18 ft)=6,631.2 ft-lb cos(20) Horizontal component, windward roof(HWR): r 12 M _[-36.7 psf sin(20)]I cos(20)X!2tan( 0)J=—349.7•ft-1b Moment (M) created by.leeward roof pressures is solved as follows: Vertical component, leeward roof(VLR): _ , Mm =[(25.6 psf cos(20)] 12 +(=6 psf)(12'ft)](6 ft)=1,411.2 ft-lb cos(20) Horizontal component, leeward roof(HLR): C12 MHLR =[25.6 psfsin(20)] cos(20)J12tan(2o)J243 2 .9 ft-lb` Moment(M) created by leeward overhang pressures is solved as follows: Vertical component, leeward overhang (VLO): Mwo =[(25.6 psf cos(20)] 2 ft +(-6 psf)(2 ft)](-1 ft)=-39.2 ft-lb cos(20)) i :" Horizontal component, leeward overhang(HLO): 2 ft X_2tan(20)J MHLo =[25.6 psfsin(20)]I _-68.ft-lb cos(20) 2 The total overturning moment per ft of roof width = 10,174.3 ft-lb 8-56 COASTAL CONSTRUCTION MANUAL 1 Volume II a DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE 8:5. ROOF UPLIFT CONNECTOR LOADS (concluded) Solving for uplift load:F = 10174.3 ft-lb/roof span ft= 10,174::3 ft-lb/24 ft=424 lb Assuming ihe uplift forces are calculated',for a 1-ft-wide section of the roof, the unit uplift connector force can be expressed as fw=424 plf. ' . Note: This,solution matches the information in Table 8-6.: 7P' EXAMPLE 8.6. LATERAL DIAPHRAGM LOADS FROM WIND PERPENDICULAR l TO RIDGE Legend Tributary area for roof diaphram I=Tributary area for floor diaphram • Leeward side (-)pressures Windward side • (+)pressures Illustration A.Lateral diaphragm loads from wind perpendicular to building ridge Given: • Roof span of 24.ft ••. 7:12 roof pitch. .. The wind load is based on 150 mph; Exposure C at 33-ft mean roof height •. The building is enclosed From Example.8.5, for the same site condition, the ASD velocity pressure q= 29:38 psf COASTAL CONSTRUCTION MANUAL ;; 8-57 8 DETERMINING SITE-SPECIFIC LOADS Volume II EXAMPLE 8.6. LATERAL DIAPHRAGM LOADS FROM WIND PERPENDICULAR TO RIDGE (continued) Find: The roof diaphragm load using the envelope procedure for low-rise buildings (see Figure 28.4-1 in ASCE 7-10). Solution: The roof diaphragm load using the envelope procedure for low-rise buildings can be found as follows: • -Lateral loads (see Illustration A) into the roof diaphragm are a function of roof slope and wall loads tributary to the roof diaphragm. • Pressure coefficients for elements of the roof GCp2 and GCp fare given in Table A. Table A. Pressure Coefficients for Roof and Wall Zones Diaphragm Zone GC,, GC, Windward 0.18 0.56 Wall interior zone Leeward 0.18 -0.37 Windward 0.18 0.69 Wall end zone Leeward 0.18 - -0.48 Roof diaphragm j Windward 0.18 0.21 Roof interior zone ? Leeward 0.18 -0.43 Windward 0.18 -0.53 Roof end zone', - Leeward 0.18 0.27 I I Windward 0.18 0.53 i I Wall interior zone - .. Leeward 0.18 -0.43 Floor diaphragm Windward 0.18 0.80 Wall end zone - - - - -- - Leeward 0.18 -0.64 • GC' is determined using the Enclosure Classification (enclosed building in this example) and. Table 26.11-1 from ASCE 7-10 • GCpfis determined using Figure 28.4-1 'in ASCE 7-10 - • Both interior zone and end zone coefficients are used to establish an average pressure on the wall and roof. The design wind pressure is determined from Equation 8.14 (q = qy in this case) as,follows: P. q I GCpf—GCp, I Step 1: Roof Diaphragm • L= leeward • W/=windward 8-58 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE 8.6. LATERAL DIAPHRAGM LOADS.FROM WIND PERPENDICULAR TO RIDGE (continued} • w=wall Wall interior zone - pww:=29.38 psf(0.56—0.18)=11.16 psf pLw =29.38 psf(-0.37—0.18)==16.16 psf Sum=11.16 psf+ —16.16psf I=27.3 psf(note that leeward and:windward forces are acting in the same direction) Wall end zone pww =29.38 psf(0.69—0.18)=14.98 psf pLw =29.38 psf(=0.48—0.18)==19:39 psf Sum=14.98 psf+ —19.39 psf l=34.4 psf (note that leeward and windward forces are acting in the same direction)- Under the procedures and notes shown in Figure 28.4-1 of ASCE 7--10, end zones extend a minimum of 3 ft at each end of the wall. For long or tall walls, end zone lengths are based on 10 percent of the least horizontal dimension or 40 percent of the mean roof height,whichever is smaller, but not less than either 4 percent.of the least horizontal dimension or 3 ft at each end of the wall;The end zone width where the pressures:are applied is 3 ft. • Ilie average pressure on the wall is: P [34.4,psf(6 ft)+27.3 psf(24 'ft—6 ft)] 29.1 psf 24 ft . where: 24 ft=building length assumed to be equal to the roof span for purposes of accounting for average effects of pressure differences at end zones and interior zones Roof interior zone - pWw.=29.38 psf(0.21-0.18)=0.88-psf PLw =29.38 psf(-0.43—0.1:8)=-17.92 psf Sum=0.88 psf+ -17.92 psf I = 8,8 psf(note that leeward-and windward forces are acting in the same direction) Roof end zone pww =29.38 psf(0.27-0.18)=2.64 psf • COASTAL CONSTRUCTION MANUAL ' 8-59 8 DETERMINING SITE-SPECIFIC LOADS Volume II EXAMPLE 8.6. LATERAL DIAPHRAGM !LOADS FROM WIND"PERPENDICULAR TO RIDGE (concluded) p w =29,38 psf(-0.53—0.18)=—20.86 psf Sum=2.64 psf+I-20.86 psf I=23.5 psf (note that leeward and windward forces are acting in the same direction) • The average pressure on the roof is: 23.5 psf(6 ft)+18:8 psf(24 ft—6 ft) P= 24 ft ' =19.98 psf The roof diaphragm will take its load plus half the load of the 8-ft-tall wall below. w,00 f = 1 2(29:1 psf)(8 ft)+19.98 psf(7 ft)=256.3 plf Step 2:-Floor Diaphragm • The floor diaphragm loads are based on;the maximum MWRFS coefficients associated with a 20-degree roof slope.It is assumed that the floor diaphragm tributary area is the height:of one 8-ft wall plus 1:ft to account for floor framing depth. Wall interior zone •.. I , =29.38 psf(0.53-0.18).=10.28 psf PLw =29.38:psf(-0.43—0.18)=—17.92 psf Sum=10.28 psf+ =17.92 psf =28.2 psf (note that leeward and windward forces are acting in the same direction) Wall end zone: pww =29,38 psf(0.80—0.18)=18.22'psf =29 38 psf 0 64 0.18) 24.09. sf pLw - • P (— - —— p Sum=18.22 psf+ -24.09 psf.=42.3 psf (note that leeward and windward forces are-acting in - the same direction) The average pressure on the-Wall is: P= 42.3.psf(6 ft)+28.2 psf(24 ft—G ft) =31.73 psf 24ft The floor diaphragm load is based on a 9-.ft tributary height obtained from adding the height of one 8-ft wall plus ft to account for the floor framing depth. w fanr =31.73.psf(9 ft)=286 plf . Note: This solution matches the information in Table 8-7 8-60 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 8.7.3 Components and Cladding ASCE 7-10 defines components and cladding (C&C) as "... elements of the building envelope that do not qualify as part of the MWFRS." These elements include roof sheathing, roof coverings, exterior siding, windows, doors, soffits, fascia, and chimneys. The design and installation of the roof sheathing attachment may be the most critical consideration because the attachment location for the sheathing is where the uplift load path begins (load path is described more fully in Chapter 9 of this Manual). C&C pressures are determined for various "zones" of the building. ASCE 7-10 includes illustrations of those zones for both roofs and walls. Illustrations for gable, monoslope, and hip roof shapes are presented. The pressure coefficients vary according to roof pitch (from 0 degrees to 45 degrees) and effective wind area (defined in ASCE 7-10). C&C loads act on all elements exposed to wind. These elements and their attachments must be designed to resist these forces to prevent failure that could lead to breach of the building envelope and create sources of flying debris. Examples of building elements and their connections subject to C&C loads include the following: Li Exterior siding L: Roof sheathing • Roof framing • Wall sheathing LI Wall framing (e.g., studs, headers) [; Wall framing connections (e.g., stud-to-plate, header-to-stud) Roof coverings C Soffits and overhangs L: Windows and window frames r i Skylights Li Doors and door frames, including garage doors L: Wind-borne debris protection systems ri Any attachments to the building (e.g., antennas, chimneys, roof and ridge vents, roof turbines) Furthermore, individual MWFRS elements of shear walls and roof diaphragms (studs and chords) may also act as components and should also be analyzed under the loading requirements of C&C. Figure 8-20 shows the locations of varying localized pressures on wall and roof surfaces. The magnitude of roof uplift and wall suction pressures is based on the most conservative wind pressures in each location for given roof types and slopes in accordance with Figure 30.4 of ASCE 7-10. As noted previously, prescriptive COASTAL CONSTRUCTION MANUAL 8-61 8 DETERMINING SITE-SPECIFIC LOADS q Volume II \PA ©_sue t+ ONi II li 1 A 2 A o' i' �� 4 3` t, y a ti Q t o r,©i ic,, �Q` ` Q -�r4�.' mod', t- NOTE Edge zone dimension,A, is measured as the horizontal projection on the building roof and walls. A=the smaller of 10 percent of the least horizontal dimension of the building(i.e. either L or W) or 40 percent of the mean roof height(MRH),,but not less than either 4 percent of the least [ horizontal dimension or 3 feet. II L=length W=width Figure 8-20. Components and cladding wind pressures standards can be used to simplify the calculation of C&C design loads. Examples of prescriptive C&C design load tables for purposes of illustration are included in this Manual as follows: E Roof and wall suction pressures (see Table 8-8). Application of ASCE 7-10 provisions and typical assumptions used to derive the tabulated load values are addressed in Example 8.7. Suction pressures are used to size connections between sheathing and framing and to size the sheathing material itself for wind induced bending. In ASCE 7-10, there is no adjustment for effective wind areas less than 10 square feet; therefore, sheathing suction loads are based on an effective wind area of 10 square feet. E Lateral connector loads from wind and building end zones (see Table 8-9).Application of ASCE 7-10 provisions and typical assumptions'used to derive the tabulated load values are addressed in Example 8.8. Lateral connector loads from wind are used to size the connection from wall stud-to-plate, wall plate-to-floor, and wall plate-to-roof connections to ensure that higher C&C loads acting over smaller wall areas can be adequately resisted and transferred into the roof or floor diaphragm. In ASCE 7-10, the effective wind area for a member is calculated as the span length times an effective width of not less than one-third the span length. For example, the effective area for analysis is calculated as h2/3 where h represents the span (or height) of the wall stud. 8-62 COASTAL CONSTRUCTION MANUAL q Volume II DETERMINING SITE-SPECIFIC LOADS 8-. - Example load tables and example problems are derived from more wind load procedures provided in the WFCM-2012 load Tables 8-8 and 8-9 are'not intended to replace requirements of the building code or reference standard for the actual design of C&C attachments for a building. Table 8-8. Roof and Wall Sheathing Suction Loads(based on ASD design), psf(33-ft mean roof height, Exposure C) Wind Speed(a)(mph) ' 110 115 120 130 140 150 160 170 180 Sheathing Location Roof, suction pressure(b)(c)(psf) Zone 1 18.6 20.4 22.2 26.0 30.2 34.7 39.4 44.5 44.9 Zone 2 31.3 34.2 37.2 43.7 50.7 58.2 66.2 74.7 83.8 Zone 2 Overhang 34.8 38.0 41.4 48.5 56.3 64.6 73.5 83.0 93.1 Zone 3 47.1 51.5 56.0 65.8 76.3 87.5 99.6 112.4 126.1 Zone 3 Overhang 58.5 63.9 69.6 81.6 94.7 108.7 123.7 139.6 156.5 Wall,suction pressure(b)(c) (psf) Zone 4 20.2 22.1 24.1 28.2 32.8 37.6 42.8 48.3 54.1 Zone 5 25.0 27.3 29.7 34.9 40.4 46.4 52.8 59.6 66.8 �`� �®� (a) 700-year wind speed,3-sec gust. (b) Roof and wall sheathing suction loads are based on 33-ft mean roof height and Exposure C(see Example 8.7). (c) Loads based on minimum effective area of 10 ft2 Table 8-9. Lateral Connector Loads from Wind at Building End Zones(Based on ASD Design), plf(33-ft mean roof height, Exposure C) Wind Speed(a)(mph) Wall Height 110 115 120 130 140 150 160 170 180 (ft) Lateral connector loads(MGM)for wall zone 5(plf) 8 92 101 110 129 150 172 196 221 248 10 110 120 131 154 179 205 233 263 295 12 127 139 151 177 206 236 269 303 340 14 143 156 170 200 231 266 302 341 383 16 158 173 188 221 256 294 335 378 423 1 (a) 700-year wind speed,3,-sec gust. .\ \� � (b) Lateral connector loads are based on 33-ft mean roof height and Exposure C(see Example 8.8). �P J 1� -o. 4.' (c) Lateral connector loads are tabulated in pounds per linear ft of wall.Individual connector loads can be [��'�o calculated for various spacing of connectors(e.g.,for spacing of connectors at 2 ft o.c.,the individual �`Q`\i connector load would be 2 ft times the tabulated value). l' ! (d) Loads based on minimum area of(wall height)2/3 - isiI•ii ;i sltsi:;, 1 . . ,\mot\�c�¢ COASTAL CONSTRUCTION MANUAL 8-63 8 DETERMINING SITE-SPECIFIC LOADS Volume II f, ` EXAMPLE 8.7. ROOF SHEATHING.SUCTION LOADS Given: • The wind load is based on 150 mph, Exposure C at.33-ft.mean roof height • The building is enclosed • • From Example 8.4, for the same site condition, the ASD velocity pressure q= 29.38 psf • The internal pressure coefficient for roof and wall sheathing is GCpf= 0.18 . . Find:"Roof sheathing and wall sheathing suction loads using the C&C-"coefficients specified in Figure 30.4 of ASCE 7-10. For cladding and fasteners, the effective wind:area should not be greater than the area that is tributary to an individual fastener. In ASCE 7-10, there is no adjustment for wind areas less than 10 ft2;therefore, sheathing suction loads are based on an effective wind area of 10 ft2 for different zones on the roof. Solution: The roof sheathing and wall sheathing suction loads can be determined using the C&C ;coefficients specified in Figure 30.4 of ASCE'7710, as follows: • The design wind pressure is determined;from Equation 8.14 (where q = qh in this case) as • follows: P=q I GCpf GC pi I • Determine the roof sheathing suction load pressure:coefficients using Figure 30.4 of ASCE 7-10 as follows: Step.1:Roof sheathing suction loads pressure coefficients Pressure coefficient equations developed from C&C, Figure 30.4, graphs of ASCE 7-10 coefficients: log( A C100) - Zone 1:GCpf=.0.9-0.1 10 =-1.0 log 100 log A (1001; Zone 2:GCpf --1.1-0.7 i0 gg(100 • ' Zone 2 Overhang:.GCpf =—2.2 8-64 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE 8.7. ROOF SHEATHING SUCTION LOADS (concluded). logl 1 O J Zone3:GCpf =-1.7-1.1 (\ 10 =-2.8 logl 100) log A Zone 3 O_verhang:GCp f =2.5—1.2 10 =—3.7 log l 100) Step 2:Wall sheathing suction loads pressure coefficient Pressure coefficient equations developed from C&C, Figure 30.4 graphs of ASCE 7-10 coefficients: log( 00 — 5 ) Zone 4:GCpf:=-0.8 0.3 i0 .=-1.1 -log 500 log.C500) Zone 5: GCpf =-0.8-0.6 : 10 --1.4. log l 500 : Step 3:For all zones—internal pressure coefficient GCpI= +/-0.18 Step 4: Calculate roof sheathing and wall sheathing suction pressures for all zones using Equation 8.14 Zone 1:p=29.38 psf(-1—0.18)=-34.7 psf Zone 2:p=29.38 psf(-1.80.18)=—58.2 psf Zone 2 Overhang: p=29.38 psf(-2.2)=—64.6 psf Zone 3::p=29.38 psf(-2.8=0.18)=—87.5 psf.. Zone 3 Overhang:p=29.38 psf(-3.7)=—108.7 psf Zone 4:p=29.38 psf(-1.1—0.18)=—37.6 psf. Zone 5: p=?9.38 psf(-1.4=0.18)=—.46.4 psf Note: This solution matches the information in Table 8-8. COASTAL CONSTRUCTION MANUAL 8-65 8 DETERMINING SITE-SPECIFIC LOADS Volume II . EXAMPLE 8.8. LATERAL CONNECTION FRAMING LOADS FROM WIND Given: • Wind load is based on 150 mph, Exposure C at 33-ft mean roof height, and wall and diaphragm framing as shown in Illustration A . . • Building is enclosed . . • Wall height is 10 ft • Stud spacing is 16 in. o.c., S • Sheathing effective area is 10 ft2. . • ASD velocity pressure q= 29.38 psf(from Example 8.5) _ •. . • Wall suction equations for Zone 4 and Zone 5 are provided in Example 8.7 Internal pressure coefficient for wall sheathing is GCp1= +I- 0.18 • Floor or roof diaphram framing '. • - 1 Lateral framing Stud , o loads c 1 Floor diaphram framing Illustration A. Lateral connector loads for wall-to-roof and wall-to-floor connections Find::Framing connection requirements at the top and base of the wall. Solution: The connector load can be determined as follows: 8-66 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 ,qq^ if EXAMPLE 8.8. LATERAL CONNECTION FRAMING LOADS FROM WIND (concluded) • C&C coefficients are used • When determining C&C.pressure.coefficients, the effective wind area equals the tributary area . of the framing members • For long and narrow tributary areas, the area width may be increased to one-third the framing member span to account for actual,load distributions . • The larger area results in lower average wind pressures • The.increase in width for long and narrow tributary areas applies only to calculation of wind pressure coefficients • • Determine the tributary area and pressure coefficient GCpf for the wall sheathing: Stud effective wind area equals 13.33 ft2. The minimum required area for analysis is h2/3=33.3 ft2, where h is 10 ft • In accordance with ASCE 7-10, the pressure coefficient, GCp f, for wall sheathing can be determined based on a minimum effective wind area of 33.3 ft2 as follows: (33.3 ' logy 500) Zone 5: GCp f =—0.8—.0.6 . . \r 10 =—1.22 . logl 500) The design wind pressure is determined as follows from Equation 8.14: p=q(GCp f—GCp,) . Zone 5:p=29.38 psf(-1.22—0'18)._-41.13 psf ' The required capacity of connectors assuming load is based on half the wall height: Zone 5:w=41.13psf 10ft J=205p1f Note: This solution matches the information in Table 8-9. 8.8 Tornado Loads WARNING Tornadoes have wind speeds that vary based on the magnitude of the event; more severe tornadoes have wind speeds that are Safe rooms should be located significantly greater than the minimum design wind speeds outside known flood prone areas, including the 500-year floodplain, required by the building code. Designing an entire building and away from any potential large to resist tornado-force winds of EF3 or greater based on the debris sources. See Figure 5-2 Enhanced Fujita tornado damage scale (in EF2 tornadoes, of FEMA 320 for more direction large trees are snapped or uprooted) may be beyond the realm regarding recommended siting for a safe room. COASTAL CONSTRUCTION MANUAL 8-67 8 DETERMINING SITE-SPECIFIC LOADS Volume II of practicality and cost-effectiveness, but this does not mean that solutions that provide life-safety protection cannot be achieved while maintaining cost-effectiveness. A more practical approach is to construct an interior room or space that is "hardened" to resist not only tornado-force winds but also the impact of wind-borne missiles. FEMA guidance on safe rooms can be found in FEMA 320, Taking Shelter from the Storm: Building a Safe Room for Your Home or Small Business (FEMA 2008c), which provides prescriptive design solutions for safe rooms of up to 14 feet x 14 feet. These solutions can be incorporated into a structure or constructed as a nearby stand-alone safe room to provide occupants with a place of near-absolute protection. The designs in FEMA 320 are based on wind pressure calculations that are described in FEMA 361, Design and Construction Guidance for Community Safe Rooms (FEMA 2008a). FEMA 361 focuses on larger community safe rooms, but the process of design and many of the variables are the same for smaller residential safe rooms. An additional reference,ANSI/ICC 500-2008 complements the information in FEMA 320 and FEMA 361 and is referenced in the 2012 IBC and 2012 IRC. Safe rooms can be designed to resist both tornado and hurricane hazards, and though many residents of coastal areas are more concerned with hurricanes, tornadoes can be as prevalent in coastal areas as they are in inland areas such as Oklahoma, Kansas, and Missouri. Constructing to minimum requirements of the building code does not include the protection of life-safety or property of occupants from a direct hit of large tornado events. Safe rooms are not recommended in flood hazard areas. 8.9 Seismic Loads This Manual uses the seismic provisions of ASCE 7-10 to illustrate a method for calculating the seismic base shear. To simplify design, the effect of dynamic seismic ground motion accelerations can be considered an equivalent static lateral force applied to the building. The magnitude of dynamic motion, and therefore the magnitude of the equivalent static design force, depends on the building characteristics, and the spectral response acceleration parameter at the specific site location. The structural configuration in Figure 8-21 is called an "inverted pendulum" or "cantilevered column" system. This configuration occurs in elevated pile-supported buildings where almost all of the weight is at the top of the piles. For a timber frame cantilever column system,ASCE 7-10 assigns a response modification factor (R) equal to 1.5 (e.g., R= 1.5). For wood frame,wood structural panel shear walls,ASCE 7-10 assigns an R factor equal to 6.5. The R factor of 1.5 can be conservatively used to determine shear for the design of all elements and connections of the structure. An R factor of 1.5 is not permitted for use in Seismic Design Categories E and F per ASCE 7-10. ASCE 7-10 contains procedures for the seismic design of structures with different structural systems stacked vertically within a single structure. Rules for vertical combinations can be applied to enable the base of the structure to be designed for shear forces associated with R=1.5 and the upper wood frame, wood structural panel shear wall structure to be designed for reduced shear forces associated with R=6.5. ASCE 7-10 also provides R factors for cantilever column systems using steel and concrete columns. A small reduction in shear forces for steel piles or concrete columns could be obtained by using what ASCE 7-10 calls a "steel special cantilever column system" or a "special reinforced concrete moment frame," both of which have an R = 2.5. However, these systems call for additional calculations, connection design, and 8-68 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 d Figure 8-21. Effect of seismic forces on supporting piles quivalent static lateral seismic force Ground ,,,e 1I :: Resisting 1, 1, „ ii forces in soil II II II II; II II - II II II II, II . II II II 0Resisting : ,, II �� 11 II II` II II forces in „ „ „ 1, i i „ Soil 1, ,, ,, ,,.. ii ii detailing, which are not commonly done for low-rise residential buildings. An engineer experienced in seismic design should be retained for this work, and builders should expect larger pile and column sizes and more reinforcing than is normally be required in a low-seismic area. Total seismic base shear can be calculated using the Equivalent Lateral Force (ELF) procedure of ASCE 7-10 in accordance with Equation 8.15. (16 EQUATION 8.15. SEISMIC BASE SHEAR BY EQUIVALENT LATERAL FORCE PROCEDURE V=C5W (Eq. 8.15a) = SDS c (RI I) (Eq. 8.15b) • where: V = seismic base shear CS = seismic response coefficient SDS = design spectral response acceleration parameter in the short period range R = response modification factor I = occupancy importance factor W = effective seismic weight k Lateral seismic forces are distributed vertically through the structure in accordance with Equation 8.16, taken from ASCE 7-10. COASTAL CONSTRUCTION MANUAL : 8-69 I 8 DETERMINING SITE-SPECIFIC LOADS a Volume II EQUATION 8.16. VERTICAL DISTRIBUTION OF SEISMIC FORCES Fx =CvxV (Eq. 8.16a) wxhx C =vxn wjhk =1 (Eq. 8.16b) where: Fx = lateral seismic force induced at any level Cvx = vertical distribution factor V = seismic base shear w,and wx = portion of the total effective seismic weight of the structure (w) located or assigned to level i or x h,and hx = height from the base to Level i or x k = exponent related to the structure period; for structures having a period of 0.5 sec or less, k=1 The calculated seismic force at each story must be distributed into the building frame. The horizontal shear forces and related overturning moments are taken into the foundation through a load path of horizontal floor and roof diaphragms, shear walls, and their connections to supporting structural elements.A complete seismic analysis includes evaluating the structure for vertical and plan irregularities, designing elements and their connections in accordance with special seismic detailing, and considering structural system drift criteria. Example 8.9 illustrates the use of basic seismic calculations. ,Nav, EXAMPLE 8.9. SEISMIC LOAD Given: • SDs for the site=2/3FaSs,which is determined to be 2/3(1.2)(0.50) ='0.4 -• The building structure as shown in Illus Oration A. Dead load for the building is as follows:. Roof and ceiling 10 lb/ft2 Exterior walls = 10 lb/ft2 Interior Walls = 8 lb/ft2 Floor 10 lb/ft2 . Piles=409 lb each 8-70 ; COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE 8.9. SEISMIC LOAD (continued) Longitudinal Roof line shear walls Fir 6oft )i -c 35ft > L4--25ftco N I M Roof ridge 0 :... Porch: T y �< 44 ft >14 16 ft Walls . Illustration A.Building elevation and plan view of roof showing • longitudinal shearwalls;:dimensions are wall-to-wall and do not include the 2-ft roof overhang Find (using ASCE 7-10-ELF procedure):! 1. The total shear wall force 2. The shear force at the top of the Pile foundation Solution for#1: The total-shear wall force using the ASCE 7-10-ELF procedure can be determined as follows: Calculate effective seismic weight: g )( Roof/ceiling:: (10 lb/ft2 2,390 ft )Z. _ 23,900 lb Exterior walls:..(10 lb/ft2)(1,960 ft2) =19,600 lb .. Interior partitions: (8 lb/ft2)(2,000Ift2) = 16,000 lb Floor= (10 lb/ft2).(2,160 ft2) = 21,600 lb Piles: (409 lb/pile)(31 piles) =,12,679 lb Total effective seismic weight: -W= 23,900 + 19,600 lb + 16,000 lb + 21,600 lb + 12,672 lb = 93,454 lb • COASTAL CONSTRUCTION MANUAL 8-71 0 8 DETERMINING SITE-SPECIFIC LOADS Volume II EXAMPLE 8.9, SEISMIC LOAD (continued • Seismic forces are distributed vertically asfollowsi Roof level: Effective seismic weight, xroof= 23,900 lb + (0.5)(19,600) lb + (0.5)(16,000/2) lb =41,700 lb Height from base, hz roof= 18 ft wxroof(hxroof) =750,600 ft-lb Floor level: , Effective seismic weight, wxfloor= 19,600/2!lb + 16,000/2 lb +.21,600 lb + 12,679 lb = 52,079 lb:. Height from base: hx floor= 8 ft wxfloor(hxfloo)= (52,0791b)(8 ft) =410,632 ft-lb 750,600 ft-lb C roo =0.64 from Equation 8.16 f :750,600 ft-lb+416;632 ft-lb 416,632 ft-lb C for = =0.36 from Equation 8.16 750,000 ft-1b+416,632 ft-lb The force in the shear walls and at the top of the piles will vary by the R factor for the shear wall system and the pile system (e.g., cantilevered column system). • Lateral seismic force at the roof level for design of wood-frame shear walls (R= 6.5): SDS Fx roof Cvx roof V=Cvx roof R W using Equation 8.15 for Vsubstituted into Equation:8:16 (0.64)(0.•4) Fx,roof 6.5 (93,454 lb)=3,60 lb . 1.0 where: R = 6.5 for light-frame walls with plywood I = 1.0 for residential structure The design shear force for the shear walls is based on the lateral seismic force at the roof level. Total seismic force for shear wall design is 3,681 lb Solution for#2: The shear force to the top of the pile.foundation (i,e., cantilevered column system, R= 1.5).can be determined as follows: • Roof level Fx roof =C„x roofV= . SDs W using Equation 8.15 for Vsubstituted into Equation 8:16 Cvx roofR 8-72 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE 8.9. SEISMIC LOAD.(concluded) (0.64)(0.4) Fx,roof = 1.5 (93,454 lb) 15,949 lb 1.,0 • Floor level SDS Fx floor =Cvx floor =Cvx floor ' R/I . . using Equation 8.15 for V substituted into Equation 8.16 , (0.36)(0.4) Fx,floor = 1.5 . (93,454lb)„,=8,972lb 1.0 where: R = 1.5 for cantilevered column system. For vertically mixed seismic-force-resisting systems,ASCE 7-10 allows a lower R to be used below a higher R value.. .. I = 1.0 for a residential structure Total shear at the floor is based on the sum of the force at the roof level.and the floor level: Ffloor= 15,949 lb + 8,972 lb =24,921 lb 8.10 Load Combinations It is possible for more than one type of natural hazard to occur at the same time. Floods can occur at the same time as a high-wind event, which happens during most hurricanes. Heavy rain, high winds, and flooding conditions can occur simultaneously. ASCE 7--10 addresses the various load combination possibilities. The following symbols are used in the definitions of the load combinations: D = dead load L = live load E = earthquake load F = load due to fluids with well-defined pressures and maximum heights (e.g., fluid load in tank) Fa = flood load H = loads due to weight and lateral pressures of soil and water in soil Lr = roof live load COASTAL CONSTRUCTION MANUAL 8-73 8 DETERMINING SITE-SPECIFIC LOADS Volume II S = snow load '! R = rain load T = self-straining force W = wind load Loads combined using the ASD method are considered to act in the following combinations for buildings in Zone V and Coastal A Zone (Section 2.4.1 of ASCE 7-10), whichever produces the most unfavorable effect on the building or building element: Combination No. 1: D Combination No. 2: D +L Combination No. 3: D+ (Lr or S or R) Combination No. 4: D+ 0.75L+ 0.75(Lr or S or R) Combination No. 5: D+ (0.6Wor 0.7E) Combination No. 6a: D+ 0.75L+ 0.75(0.6W) + 0.75(Lr or S or R) Combination No. 6b: D+ 0.75L+ 0.75(0.7E) + 0.75S Combination No. 7: 0.6D+ 0.6W Combination No. 8: 0.6D+ 0.7E When a structure is located in a flood zone, the following load combinations should be considered in addition to the basic combinations in Section 2.4.1 of ASCE 7-10: In Zone V or Coastal A Zone, 1.5Fa should be added to load combinations Nos. 5, 6, and 7, and E should be set equal to zero in Nos. 5 and 6 C In the portion of Zone A landward of the LiMWA, 0.75FQ should be added to combinations Nos. 5, 6, and 7, and E should be set equal to zero in Nos. 5 and 6. The ASCE 7-10 Commentary states "Wind and earthquake loads need not be assumed to act simultaneously. However, the most unfavorable effects of each should be considered in design, where appropriate." The designer is cautioned that F is intended for fluid loads in tanks, not hydrostatic loads. Fa should be used for all flood loads, including hydrostatic loads, and should include the various components of flood loads as recommended in Section 8.5.11 in this chapter. It is important to note that wind and seismic loads acting on a building produce effects in both the vertical and horizontal directions. The load combinations discussed in this section must be evaluated carefully, with consideration given to whether a component of the wind or seismic load acts in the same vertical or horizontal direction as other loads in the combination. In some cases, gravity loads (dead and live loads) may counteract the effect of the wind or seismic load, either vertically or horizontally. Building elements,submerged in water have a reduced effective weight due to buoyancy. Example 8.10 illustrates the use of load combinations for determining design loads. 8-74 j COASTAL CONSTRUCTION MANUAL JI 1 Volume II DETERMINING SITE-SPECIFIC LOADS 8 ija i ' EXAMPLE 8.10.LOAD COMBINATION EXAMPLE PROBLEM " Given: Use the flood loads from Example 8.3: • . Fsta= O • Fdy,: = 909 lb • Fbrkp = 625 lb • F;= 2,440 lb • d,= 4.6.ft . Use for wind loads: • Roof span = 28 ft • Roof pitch = 7:12 • Wall height = 10 ft Wind uplift load = 33,913 lb (pre-factored with 0.6) • Exposure Category D (multiply Exposure C wind loads by 1.18 at 33 ft mean roof height) •. 1.18 is a conservative value because while the higher Exposure Category D has been factored, the lower roof height (24 ft versus 33 ft) has not. Refer to ASCE 7-10, Figure 28.6-1 for guidance. Wind direction,: 10 ft 1' 1ft — '- ----- I I I I I I II 7ft Illustration A. Side view of building COASTAL CONSTRUCTION MANUAL 8-75 8 DETERMINING SITE-SPECIFIC LOADS Volume II EXAMPLE 8.10. LOAD COMBINATION EXAMPLE PROBLEM (continued) Use for dead load: • 95,090 lb for house and piles Use for buoyancy load: . • 9,663 lb The locations given in Illustration B for the forces. Find: 1. Calculate maximum horizontal wind load that occurs perpendicular to the ridge and the floor for the example building • . 2...Find the horizontal load required for foundation design 3. Calculate global overturning moment due to horizontal loads and wind uplift (see Illustration B) Solution for#1: To determine the horizontal wind load perpendicular to the ridge, use the projected area method as follows: • For wind perpendicular to the ridge of a roof with a span of 28 ft (using Table 8-7), 7:12 roof pitch and wall height of 10 ft, Category D as shown in Illustration A, the lateral roof diaphragm load,w,.00 f, can be found by interpolation between the 24 ft and 32 ft roof span wroof values in Table 8.7: woof= (256 plf+299 plf)(0.5) =278 plf ; roof P Category' . . .: To adjust w for:Ex Exposure Cate or D due to the fact Table 8-7 assumes Exposure Category C: wroof =1.18(278 plf)=328 plf where 1.18 = Exposure D adjustment factor (33 ft mean roof height) To adjust wroo f for a wall height of 10 ft due to the fact Table 8.7 assumes a wall height of 8 ft: to ft) Wroof =(328 plf)( 8 ft I=410 plf • Determine lateral floor diaphragm load, wfoor from Table 8-7. Once more, this value needs to be,adjusted for Exposure Category D from the assumed Exposure Category C: wfloor =1:18(286 plf)= 338 plf where 1.18 -= Exposure D adjustment factor (33 ft mean roof height) 8-76 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE 8.10. LOAD COMBINATION EXAMPLE PROBLEM (continued) To adjust wroof for a wall height of 10 ft due.to the fact Table 8.7.assumes a wall height:of 8 ft: 10 ft who. =(338 plf)( 8 ft )=423 plf Finally, adjust this value to account for the reference-case in Table 8-7 assuming the lateral floor diaphragm load is from wind pressures on the,lower half of the wall above and the upper,half of the wall below the floor diaphragm. Because the structure is open below the floor diaphragm level, adjust wfoor to account for the presence of only half of the wall area used in the reference case for Table 8-7 (e.g., structure is open below first floor diaphragm): wflaor =0.5(423 plf)=212 plf • For building length = 60 ft, total horizontal shear at the top of the foundation is: Wfouudatiou = (410 plf+ 212 plf)(60 ft) =37,320 lb Solution for #2: The horizontal load required for foundation design, can be determined using the following calculations of the load combination equations given in Section 8.10: • Zone V and Coastal A Zone 5. D+ 0.6W+ 1.5Fa 6a. D+ 0.75L+ 0.75(0.6W) +.0.75(L,.or S or R) + 1.5Fa 6b. D+ 0.75L+ 0.75S+. 1.5Fa 7. 0.6D+ 0.6W+ 1.5Fa . Load combination No. 5 produces the maximum shear at the foundation for the loads considered.This load combination includes a wind load factor'adjustment of 0.6. Because the value of Wfoundario„from Solution#1 has.already been adjusted by-0.6 for ASD, it will not be further.adjusted in the calculations that follow. For flood load,the value of Fa is determined in accordance with Table 8-5. The hydrodynamic load is greater than breaking wave load, therefore, Fa for an individual pile and the foundation as. a whole (i.e., global) is calculated as:' Fa,,zd,viduag=F;+Fdy„= 2,440 lb + 909 lb = 3,349 lb Fa(globalj (1 pile)F!+ (35 piles)Fdy„ = 34,255 lb 5. Total shear:37,320 lb+1.5(34,25 51b) = 88,703 lb ' • Portion of Zone A landward`of the LiMWA _ 5. D+ 0.6W+ 0.75Fa . 6a. D+ 0.75L+ 0.75(0.6W) + 0.75(4 or S or R) + 0.75Fa COASTAL CONSTRUCTION MANUAL 8-77 8 DETERMINING SITE-SPECIFIC LOADS Volume II EXAMPLE 8.10. LOAD COMBINATION EXAMPLE PROBLEM (continued) 6b..ID+.0.75L+ 0.75S+ 0.75F, 7. 0.6D+ 0.6 W+ 0.75FQ Load combination 5 produces the maximum shear at the foundation for the loads considered. 5. Total shear:37,320+0.75(3 4,25 5 lb) = 63,011 lb Note: Considering seismic force from Example 8.8,ASD shear force at,the foundation is determined by load combination No..8: 8. Total seismic base shear= 0.7(24,921 lb) = 17,444 lb Solution for#3: To determine the factored global overturning moment due to the factored loads on ' the building, take the moments about the pivot point in Illustration B. Wroof Wdead load= Wbuoyancy= 33,913.2 lb 57,054 lb 9,663 lb (already factored with 0.6) WJloor= 12,720 lb W — 7.5ft roof 24,600lb + r -- ,c Lji I I I 111 2.5 ft IIyT 3.4 Pivot I' point F 9.33 ft ill! 2.3 ft 2.3 ft � 16.15ft >< 11.85ft � Vand non-coastal ZoneA=3,660 lb Vand non-coastal ZoneA=47,723 lb Non-coastal ZoneA=1,830 lb Non-coastal ZoneA=23,861 lb Illustration B. Loads on building for global overturning moment calculation Load Combination 7 produces the maximum overturning at the foundation for the loads considered. .-Factored global overturning moment can be calculated from the factored loads and their location of application as shown in Illustration B. Zone V and Coastal A-Zone. 8-78 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 EXAMPLE 8.10. LOAD COMBINATION EXAMPLE PROBLEM (concluded) 7. 0.6D+ 0.6 W+ 1.5Fa gives the appropriate factors to be used in calculating the factored global overturning moment From Illustration B: . . ' Mg1,bat.=(.0.6)wroof(18 ft)+(0.6)w flor(10.5 ft)+(1.5)F(4.6'ft)+(1.5)Fdr,(2.3 ft)+ Wupr ft(28 ft)—(0.6)DL(16.15 ft)+(1.5)Fb(19 ft) Mglobal =(0.6)(24,600 lb)(18 ft)+(0.6)(12,72016)(10.5 ft)+(1.5)(2,4401b)(4.6 ft)+ (1.5)(31,8151b)(2.3 ft)+(33,913 1b)(28 ft)—(0.6)(95,090 lb)(16.15 ft)+(1.5)(9,663.1b)(19 ft) =776,000 ft-lb .. . • The portionof Zone A landward of the LiMWA. 7. 0.6D+ 0.6W+ 0.75Fa gives the appropriate factors to be used in calculating the factored global overturning moment From Illustration B:, Mglobal =(0.6)wroof(18 ft)+(0.6)w or(10.5 ft)+(0.75)F(4.6 ft)+(0.75)Fdyn(2.3 ft) +Wup0(28 ft)—(0.6)DL(16.15 ft)+(.75)Fb(19 ft) . . Mglabal =(0.6)(24,600 lb)(18 ft)+(0.6)(12,7201b)(10.5 ft)+(0.75)(2,4401b)(4.6.ft) +(0.75)(31,81516)(2.3 ft)+(33,9131b)(28 ft)—(0.6)(95,090 lb)(16.15 ft) +(0.75)(9,6631b)(19 ft)=575,000 ft-lb Note:In this example, the required uplift-capacity to resist overturning is estimated by evaluating the skin friction capacity of the piles. The total pile 1 uplift capacity is approximately 908,000 ft-lb. which exceeds both calculated overturning moments and is based on the horizontal distance to each row of piles from the pivot point and the following assumptions: • Pile embedment: 19.33 ft . • Pile size: 10 in. • Coefficient of friction: 0.4 for wood piles _ • Density of sand:.128 lb/ft3 • Coefficient of lateral pressure: 09.5. • • Critical depth fir sand: 15 ft • Angle.of internal friction: 38° • • Scour depth: 5.ft • • Factor of safety: 2 COASTAL CONSTRUCTION MANUAL 8-79 8 DETERMINING SITE-SPECIFIC LOADS r Volume II The following worksheet can be used to facilitate load combination computations. Worksheet 3. Load Combination Computation Load Combination Computation Worksheet OWNER'S NAME: 1 PREPARED BY: ADDRESS: DATE: PROPERTY LOCATION: Variables D (dead load) = E(earthquake load) = L (live load) = F(fluid load) = Fa (flood load) = H(lateral soil and water in soil load) = LT(roof live load) = S(snow load) = R(rain load) = T(self-straining force) = W(wind load) = Summary of Load Combinations: 1. 2. 3. 4. 5. 6a. 6b. 7. 8. Combination No. 1 ;, D= Combination No. 2 D+L= Combination No.-3 D+ (4.or S or R) = 8-80 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE-SPECIFIC LOADS 8 Worksheet 3. Load Combination Computation.(cyoncluded) Combination No.4 D+ 0.75L+ 0.75(Lr or S or R) = Combination No. 5 D+ (0.6 Wor 0.7E) = Combination No. 6a D+ 0.75L+ 0.75(0.6W) + 0.75(Lr or S or R) = Combination No. 6b D+ 0.75L+ 0.75(0.7E) + 0.75S= Combination No. 7 0.6D+ 0.6W= Combination No. 8 0.6D+ 0.7E= When a structure is located in a flood zone, the following load combinations should be considered in addition to the basic combinations: E: In Zone V or Coastal A Zone, 1.5F,should be added to load combinations Nos. 5, 6, and 7, and E should be set equal to zero in Nos. 5 and 6. t2 In the portion of Zone A landward of the LiMWA, 0.75F,should be added to load combinations Nos. 5, 6, and 7, and E should be set equal to zero in Nos. 5 and 6. 8.11 References AF&PA (American Forest &Paper Association). 2012. Wood Frame Construction Manual for One-and Two-Family Dwellings. WFCM-12. AISI (American Institute of Steel Institute). 2007. Standard for Cold formed Steel Framing prescriptive Method for One-and Two-family Dwellings.AISI S230-07. AISC (American Institute of Steel Construction) /ICC (International Code Council). 2008. Standard for the Design and Construction of Storm Shelters.ANSI/ICC 500-2008. The American Institute of Architects. 2007.Architectural Graphic Standards. A. Pressman, ed. Hoboken, NJ:John Wiley& Sons, Inc. ASCE (American Society of Civil Engineers). 1995. Wave Forces on Inclined and Vertical Wall Surfaces. ASCE. 2005a. Flood Resistant Design and Construction.ASCE Standard ASCE 24-05. ASCE. 2005b.Minimum Design Loads for Buildings and Other Structures.ASCE Standard ASCE 7-05. ASCE. 2010.Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-10. COASTAL CONSTRUCTION MANUAL 8-81 { 8 DETERMINING SITE-SPECIFIC LOADS Volume II AWC (American Wood Council). 2009. Prescriptive Residential Wood Deck Construction Guide. AWC DCA6. Bea, R.G., T. Xu,J. Stear, and R. Ramos. 1999. "Wave Forces on Decks of Offshore Platforms."Journal of Waterway, Port, Coastal and Ocean Engineering, Vol. 125, No. 3, pp. 136-144. Camfield, F.E. 1980. Tsunami Engineering. Vicksburg, MS: Coastal Engineering Research Center. FEMA(Federal Emergency Management Agency). 2001. Engineering Principles and Practices for Retrofitting Floodprone Residential Buildings. FEMA 259. FEMA. 2006. Hurricane Katrina in the Gulf Coast. FEMA 549. FEMA. 2008a. Design and Construction Guidance for Community Safe Rooms. FEMA 361. FEMA. 2008b. Guidelines for Design of Structures for Vertical Evacuation from Tsunamis. FEMA P646. FEMA. 2008c. Taking Shelter from the Storm:Building a Safe Room for Your Home or Small Business. FEMA 320. FEMA. 2009. Hurricane Ike in Texas and Louisiana. FEMA P-757. Fox, R.W. and A.T. McDonald. 1985. Introduction to Fluid Mechanics. New York:John Wiley&Sons, Inc. ICC (International Code Council). 2008. Standard for Residential Construction in High-Wind Regions. ICC 600-2008. ICC. 2011a. International Building Code. 2012 IBC. ICC: Country Club Hills, IL. ICC. 2011b. International Residential Code for One-and Two-Family Dwellings. 2012 IRC. ICC: Country Club Hills, IL. McConnell, K., W. Allsop, and I. Cruickshank. 2004. Piers,Jetties and Related Structures Exposed to Waves: Guidelines for Hydraulic Loadings. London: Thomas Telford Publishing Sumer, B.M., R.J.S. Whitehouse, and A. Torum. 2001. "Scour around Coastal Structures: A Summary of Recent Research." Coastal Engineering,Vol. 44, Issue 2, pp. 153-190. USACE (U.S.Army Corps of Engineers). 1984. Shore Protection Manual, Volume 2. USACE. 2006. Coastal Engineering Manual. USACE. 2008. Coastal Engineering Manual. Walton, T.L.Jr.,J.P.Ahrens, C.L. Truitt, and R.G. Dean. 1989. Criteria for Evaluating Coastal Flood- Protection Structures. Coastal Engineering Research Center Technical Report 89-15. U.S.Army Corps of Engineers Waterways Experiment Station. 8-82 COASTAL CONSTRUCTION MANUAL COASTAL CONSTRUCTION MANUAL t-r _. " - �. ,. 7ii ,, - lirmilipli rik- . i i iiiii, II I ' vet " 0 11; t Designing tthe Building ,..._----_--, This chapter provides guidance on design considerations for buildings in coastal environments. The topics discussed in CROSS REFERENCE this chapter are developing a load path through elements of the building structure, considerations for selecting building For resources that augment the guidance and other information in materials,requirements for breakaway walls,and considerations this Manual, see the Residential for designing appurtenances. Examples of problems for the Coastal Construction Web site development of the load path for specific building elements are (http://www.fema.gov/rebuild/ provided, as well as guidance on requirements for breakaway mat/fema55.shtm). walls, selection of building materials, and appurtenances. 9.1 Continuous Load Path In hazard-resistant construction, the ability of the elements of a building, from the roof to the foundation, to carry or resist loads is critical. Loads include lateral and uplift loads. A critical aspect of hazard-resistant construction is the capability of a building or structure to carry and resist all loads—including lateral and uplift loads—from the roof, walls, and other elements to the foundation and into the ground. The term "continuous load path" refers to the structural condition required to resist loads acting on a building. A load path can be thought of as a chain running through the building. A building may contain hundreds of continuous load paths.The continuous load path starts at the point or surface where loads are applied, moves through the building, continues through the foundation, and terminates where the loads are transferred to the soils that support the building. Because all applied loads must be transferred to the foundation, the load path must connect to the foundation.To be effective,each link in the load path chain must be strong enough to transfer loads without breaking. COASTAL CONSTRUCTION MANUAL 9-1 9 DESIGNING THE BUILDING Volume II Buildings that lack strong and continuous load paths may fail when exposed to forces from coastal hazards, thus causing a breach in the building envelope odthe collapse of the building. The ability of a building to resist these forces depends largely on whether the'building's construction provides a continuous load path and materials that are appropriate for the harsh coastal environment. The history of storm damage is replete with instances of failures in load paths. Figures 9-1 through 9-5 show instances of load path failure. Figure 9-1. -iii 1w7,.;. Load path failure at gable t., end, Hurricane Andrew -.' f '- k,\ (Dade County, FL, 1992) " '��_ ` I P, I r * ITT., `N � 1 1 1L ' J$ . ici i, I ''' 41,E, it. �i„ _ a , '1 immi ..,, ,, ,.,„...1.:431,__„..,.z. , __.....L . ., , ,,i„_,.._.. \,.... • _ ,..... et 1, .„,lif if:/1:1 ,,k,\ , ,,,yrii._ _,-+,,,„.,..; Figure 9-2. i __ — Load path failure in — — --~- connection between home and its foundation, - ., -; .- Hurricane Fran (North . Carolina, 1996) 1 , \ V 1,' , F. , "�� 1\ A. 1\\ tp, 9-2 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9 N � , '° ,z ' rr° a ° 4 A � • '- Figure 9-3. t ; • 4'111 s . kit- ry Roof framing damage } ,� :, ;t �6' and loss due to load path . ► r; failure at top of wall/roof �� r �,' structure connection, ii\ �+ - Hurricane Charley(Punta i:_._ _. ' - Gorda, FL, 2004) 1 t,tly ' k Ink 11 , :I, I ',;� 1 • ;r. }ems} DEi x ::'. a0.�. — ..._ , '� .sue a`zr: - - ^rt.' -.: .. J' _ - -- .. . . f Figure 9-4. � �r ,► Iw�N `�,,� Load path failure in ,. , tl TM , 4 ` -- .-+ ,3.--' connections between roof :_ - --'� -_ ,;' -- ' decking and roof framing, F Hurricane Charley(Punta if_=:allmj..1:: - -_--------- „,„,..'- '� ;, " Gorda, FL, 2004) ilmairrei_ b'•_ _. Yam - -',_Y sa...- - _ _ 1 li 1/4., ' toffil,-. r \Ill ij kAe ;I I n q 4 $ •, .44" .' '. 1 .a"...- r s ( — J' a 6 '�.4 -44 - - • '4t FrJ'_,1 _F'3_ r�_ � m:-A Atf.x• 3 --.'"t.:A Sm- -*Al' 'Most load path failures have been observed to occur at connections as opposed to the failure of an individual structural member (e.g. roof CROSS REFERENCE rafter or wall stud).Improvements in codes,design,and materials over For a discussion of building the past decade have resulted in improved performance of structural envelope issues, see systems.As the structural systems perform better,other issues related Chapter 11 of this Manual. to load path—such as building envelope issues—become apparent. COASTAL CONSTRUCTION MANUAL 9-3 9 DESIGNING THE BUILDING Volume II I Figure 9-5. i Newer home damaged 9 ., - from internal pressurization and ;j '"!1 - - inadequate connections, r = ti y Hurricane Katrina(Pass _• ' -; " �:. ` Christian, MS,2005) I. i ,,�,•�`Z'r, y`! _);; ,�=ems .ar-,, _ - F- � ,, . f. I : III( jIA!flh1IIfl !J i t �� ri - ' no, f f , y� s,1t ^. yF t.••••;•,'i••Pc;} 1 • •��•i ce c '; '," A. " w I k lk a1 Yr` Load path guidance in this chapter is focused primarily on elements of the building structure, excluding foundation elements. Foundation elements are addressed in Chapter 10. Examples are provided primarily to illustrate how the load path resists wind uplift forces, but a complete building design includes a consideration of numerous other forces on the load path,including those from gravity loads and lateral loads.The examples illustrate important concepts and best practices in accordance with building codes and standards but do not represent an exhaustive collection of load calculation methods. See the applicable building code, standard, or design manual for more detailed guidance. Figure 9-6 shows a load path for wind uplift beginning with the connection of roof sheathing to roof framing and ending with the resistance of the pile to wind uplift. Links#1 through#8 in the figure show connections that have been observed during investigations after high-wind events to be vulnerable to localized failure. However, the load path does not end with the resistance of the pile to wind uplift. The end of transfer through the load path occurs when the loads from the building are transferred into the soil (see Chapter 10 for information about the interaction of foundations and soils).Adequately sizing and detailing every link is important for overall performance because even a small localized failure can lead to a progressive failure of the building structure.The links shown in Figure 9-6 are discussed in more detail in Sections 9.1.1 through 9.1.8. For additional illustration of the concept of load path, see Fact Sheet 4.1,Load Paths, in FEMA P-499 (FEMA 2010b). 9.1.1 Roof Sheathing to Framing Connection (Link#1) Link#1 is the nailed connection of the roof sheathing to the roof framing (see Figures 9-6 and 9-7). Design considerations include ensuring the connection has adequate strength to resist both the withdrawal of the nail shank from the roof framing and the sheathing's pulling over the head of the fastener (also referred to as "head pull-through"). Because of the potential for head pull-through and the required minimum nailing for diaphragm shear capacity, fastener spacing is typically not increased even where shank withdrawal strength 9-4 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9 II -.„...,‘N.„..,..,,,.....zia elj\ . , . . , Figure 9-6. Example load path for case study building t_-1Mil II1II1I 1 11 ® • • •• Link#1 • • Link#2 /. Link#3 • • - Link • #4 • •▪ • Window header 464.. . . • . 11, • • Link • #5 Load path/ • • • • • • . Link C1 .. lJ ' ,. 0% - - S 0 . . 00. 0 ... o 0 i Link#8 � Link#7 V COASTAL CONSTRUCTION MANUAL 9-5 9 DESIGNING THE BUILDING Volume II Figure 9-7. Connection of the roof sheathing to the roof . ' framing(Link#1) Link#1 • is significantly greater than that provided by a smooth shank nail.Additional strength can be added by using ring shank nails, also called deformed shank nails. The grooves and ridges along the shank act as wedges, giving the nail more withdrawal strength than a typical smooth shank nail. Fastener attachment requirements for roof sheathing to roof framing are available in building codes and design standards and are presented in terms of nailing schedules dependent on nail diameter and length, framing spacing, specific gravity of framing lumber, and wind speed. Common assumptions for calculating nailing schedules to resist wind uplift are provided in Example 9.1. Minimum roof sheathing attachment prescribed in building codes and reference prescriptive standards is 6 inches o.c. at panel edges and 12 inches o.c. in the field of the panel. EXAMPLE 9.1. ROOF SHEATHING NAIL SPACING FOR WIND UPLIFT i. :Given: • Refer to Figure 9-7 • Wind speed=150 mph (700-year wind speed, 3-sec,gust), Exposure Category D • Roof sheathing= 7/16-in. oriented strand board (OSB) • Roof framing specific gravity, G = 0.42 • 8d common nail has withdrawal capacity of 66 lb/nail per the NDS -. Find: 1. Nail spacing for the perimeter edge zone for rafter spacing of 16 in. o.c.. 2. Nail spacing for the perimeter edge zone for rafter spacing of 24 in. o.c. 9-6 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9 EXAMPLE 9.1. ROOF SHEATHING NAIL SPACING FOR WIND UPLIFT (continued) Solution for#1: The following calculations are used to determine the nail spacing: • From Table 8-8, the maximum wind suction pressure (based on ASD design) is: p= 108.7 psf acting normal to the roof surface (Zone 3 overhang) for Exposure Category C The maximum wind suction pressure for Exposure D is: p= 108.7 psf(1.18)=128.3 psf where: 1.18 =the adjustment factor from Exposure C to Exposure D at 33-ft mean roof height (see Example 8.10) • The assumed minimum tributary area for calculation of this pressure is 10 ft2 in accordance with Example 8.7 • For framing at 16 in. o.c., roof suction loads in plf are: P=128.3 psf 16 in. =171.0 plf 12 in./ft • Nail spacing: 66 lb/nail Spacing= =0.386 ft=4.6 in. 171.0 plf Rounding down to next typical spacing value, specify 4-in.spacing Solution for#2: The.following calculations are used to determine the nail spacing: • From Table 8-8, the maximum wind suction pressure is: p= 108.7 psf acting normal to the roof surface (Zone 3 overhang) for Exposure Category C See Figure 8-18 and Table 8-8. The maximum wind suction pressure for Exposure D is: p= 108.7 psf(1.18)=128.3 psf where: 1.18 = adjustment factor from Exposure C'to Exposure D at 33-ft mean roof height (see Example 8.10). • The assumed minimum tributary area for calculation of this pressure is 10 ft2 in accordance with Example 8.7. COASTAL CONSTRUCTION MANUAL 9-7 9 DESIGNING THE BUILDING Volume II EXAMPLE 9.1. ROOF SHEATHING NAIL2^SPACING FOR WIND UPLIFT (concluded) • For framing at 24 in. o.c., roof suction loads on a plf basis is: 24 in. P'=128.3:psf- =256.5 plf 12 in./ft • Nail spacing: 66-1b/nail Spacing= 256:5 plf =0.26 ft=3.09 in. Rounding down to next typical spacing value, specify 3-in.spacing Note: Edge zone nail spacing associated with Zone 3 OH pressures is conservative for other edge,zone locations. Although increased nail spacing may.;be:calculated for an edge zone away from the building , corners, it is recommended that the same nailing schedule be used throughout all edge zones. 9.1.2 Roof Framing to Exterior Wall (Link#2) Link#2 is the connection between the roof framing member (truss or rafter) and the top of the wall below (see Figures 9-6 and 9-8) for resistance to wind uplift. Metal connectors are typically used where uplift forces are large. A variety of metal connectors are available for attaching roof framing to the wall. Manufacturers' literature should be consulted for proper use of the connector and allowable capacities for resistance to uplift. Prescriptive solutions for the connection of the roof framing to the wall top plates are available in building codes and wind design standards. One method of sizing the connection between the roof framing and the exterior wall is provided in Example 9.2. Figure 9-8. Connection of roof Link#2 framing to exterior wall Roof truss (Link#2) 11000/ I► 4V ® Wall studs Double top plate Metal hurricane connector f . Window header 9-8 COASTAL CONSTRUCTION MANUAL • Volume II DESIGNING THE BUILDING 9 v. EXAMPLE 9.2. ROOF-TO-WALL CONNECTION FOR UPLIFT. • Given: • Refer to Figure 9-8 and Illustration A Location Wind;dire of of uplift •. Wind speed= 150 mph, Exposure D • • Mean roof height= 24 ft (:) •)( • Rafter spacing= 24 in. o.c. • Hip rafter span = 14 ft - 111111111111111 • Roof pitch = 7:12 • Roof dead load= 10 psf • Wall height= 10 ft Illustration'A. Location of uplift connection on hip roof Find: Determine the required connector size for wind uplift using prescriptive tables for wind uplift loads (i.e., find the uplift and lateral loads for the connector). Solution: The required connector size,using wind uplift prescriptive tables can be determined. as follows: ' Uplift • For this example, the maximum hip rafter span = 14 ft • To use Table 8-6, the uplift strap connector load should be obtained for a 28-ft roof width (e.g., 28,ft is 2 times the 14-ft maximum hip rafter span; see the note at the end of this Example) ' • Interpolating between the 24-ft and 32-ft roof span uplift strap connector loads for 150 mph wind speed in Exposure C is: (424 plf:+534 plf) _479 plf 2 Adjust to Exposure Category.D by multiplying by 1.18 (see Example 8.10) 1.18(479 plf)=565.2 plf ' • For rafter framing at 2 ft on center, the uplift connector force is: ' (565.2 plf)(2 ft)=1,1311b Lateral • The lateral load on the connector is = 205 plf(see Table 8-9) for Exposure Category C • Adjusting for Exposure Category D ' COASTAL CONSTRUCTION MANUAL 9-9 9 DESIGNING THE BUILDING Volume II EXAMPLE 9.2. ROOF-TO-WALL CONNECTION FOR UPLIFT (concluded) • 1.18(205 plf) = 241.9 plf for rafter framing at 2 ft o.c., the lateral connector force at each rafter is: (241.9 plf)(2 ft)=484 lb Note: Although the connector forces shown in Table 8-9 assume a gable roof requirements can be conservatively applied for attaching the hip rafter to the wall. See Table 2.5A, Wood Frame Construction Manual for One- and Two-Family Dwellings (AF&PA 2012). Note that the example roof uses both a gable roof and hip roof framing. For simplicity, the same rafter connection is often used at each connection between the rafter and wall framing. In addition, although smaller forces are developed in shorter hip roof rafter members, the same connector is typically used at all hip rafters. Figure 9-9 shows truss-to-wood wall connections made with metal connectors. Figure 9-10 shows a rafter-to- masonry wall connector that is embedded into the concrete-filled or grouted masonry cell. Figure 9-9. — Connection of truss to "�,;, , wood-frame wall Itillit • e e o"..11 - TT , •111:10 siiiP ..t. .1 ,itir _..--------7" is c ilitli 9.1.3 Wall Top Plate to Wall Studs (Link #3) Link#3 is the connection between the wall top plates and the wall stud over the window header(see Figures 9-6 and 9-11). The connection provides resistance to the same uplift force as used for the roof framing to the exterior connection minus the weight of the top plates. An option for maintaining the uplift load path is the use of metal connectors between the top plates and wall studs or wood structural panel sheathing(see Figure 9-12). The uplift load path can be made with wood structural panel wall sheathing, particularly when the uplift and shear forces in the wall are not very high. Guidance on using wood structural panel wall sheathing for resisting wind uplift is provided in ANSI/AF&PA SDPWS-08. The lateral load path (e.g., out-of-plane wall loads) is maintained by stud-to-top plate nailing. 9-10 COASTAL CONSTRUCTION MANUAL • Volume II 8 DESIGNING THE BUILDING 9 , 1 Roof trusses at 24 inches Connector(typical) on center maximum Oversize washer Pressure-treated Direct roof truss anchorinstalled accordingto according to design , ® !r top plate, as required (typical) ��, �' / (2x4 maximum) manufacturers � �i specifications �1 '..A O° Reinforced 1/2 inch anchor T.(I� �a:�e bond beam ' !!i hescenby d stalN INvr �I barrier manufacturer'sS ® v► specifications 1 ® � �aO. Roof truss anchored /' Roof truss anchored to top plate in bond beam e Reinforced concrete masonry wall 110 Grout stop Figure 9-10. Roof truss-to-masonry wall connectors embedded into concrete-filled or grouted masonry cell (left-hand side image has a top plate installed while the right-hand side does not) Link#3 Figure 9-11. Connection of wall top Roof truss irr .k..,..s..., plate-to-wall stud `®� (Link#3) � _% \ -'• Wall studs $ •. Double . , I • top plate ;i / '• Metal hurricane / I . connector : Wall sheathing ` ;.-- `" r- L . -";ir': - c I Window header For masonry or concrete walls, the wood sill plate is typically connected by anchor bolts, cast-in straps, or other approved fasteners capable of maintaining a load path for uplift, lateral, and shear loads. Anchorage spacing varies based on the anchorage resistance to pullout, the resistance of the plate to bending, and strength of the anchorage in shear. Anchorage must be spaced to resist pullout, and the plate must resist bending and splitting. Placing anchor bolts close together assists in reducing the bending stress in the plate. COASTAL CONSTRUCTION MANUAL 9-11 i 9 DESIGNING THE BUILDING Volume II 1 Figure 9-12. Wall top plate-to-wall 01110\11111011. stud metal connector Top plate S. ll o 0 .001t0t. 0Vill0 a:P.W.- :- ''''' 0 :00 0 Wall-plate-to wall-stud connector Wall stud 4 9.1.4 Wall Sheathing to Window Header (Link#4) Link #4 is the connection between the wood structural panel wall sheathing and the window header (see Figures 9-6 and 9-13). The connection maintains the uplift load path from the wall top plates for the same force as determined for the roof connection to the,wall minus additional dead load from the wall. Options for maintaining the uplift load path include using metal connectors between the wall studs and header or wood structural panel sheathing (see Figures 9-13,and 9-14). The uplift load path is frequently made with wood structural panel wall sheathing, particularly when the uplift and'shear forces in the wall are not very high.Additional design considerations include the resistance of the window header to bending from gravity loads, wind uplift, and out-of-plane bending loads from wind. In masonry construction, a masonry or concrete bond beam, or a pre-cast concrete or masonry header, is often used over the window opening. Design considerations for this beam include resistance to bending in both the plane of the wall and normal to the wall. Resistance to bending is accomplished by placing reinforcing steel in the bond beam. Reinforcing steel must be placed in the bond beam in order for the beam to adequately resist bending stresses.The design of these members is beyond the scope of this Manual; therefore, the prescriptive methods presented in ICC 600-2008, or concrete and masonry references should be used. 9.1.5 Window Header to Exterior Wall (Link#5) Link#5 is the connection from the window header to the adjacent wall framing (see Figures 9-6 and 9-14). Link #5 provides resistance to wind uplift and often consists of a metal strap or end-nailing the stud to the header. The total uplift force is based on the uplift forces tributary to the header. Maintaining the load path for the out-of-plane forces at this location includes consideration of both the positive (inward) and the negative (outward) pressures from wind. This load path is commonly developed by the stud-to-header nailing. One method of sizing the connection between the window header and the exterior wall is provided in Example 9.3. 9-12 COASTAL CONSTRUCTION MANUAL I 1 i Volume II DESIGNING THE BUILDING 9 i u Figure 9-13. Wall stud � Connection of wall • • " sheathing to window Structural header(Link#4) sheathing • ; tea. M �,k i." - -- - - Wall stud rir Window * \ ---+ `i# header \� •- • 4,4 Pe z . _...__2-,•-,...;..--- :. Link#4 )111101114 r Jack studs --'r Figure 9-14. Connection of window ir V header to exterior wall (Link#5) Metal stap I ........j i I ��o Wall stud )'%, Window header I Jack studs , kil ' ' Link#5 COASTAL CONSTRUCTION MANUAL II 9-13 6 9 DESIGNING THE BUILDING Volume II . fi: EXAMPLE 9.3..UPLIFT AND LATERAL:LOAD PATH AT WINDOW HEADER Given: • Refer to Figure 9-14 and Illustration A • Unit uplift load on window header = 565.2 plf(from Example 9.2) • Unit lateral load on header=.241.9 plf(from Example 9.2) • Header span,= 14 ft Find: . • Uplift and lateral load for connection of the header to the wall framing. Trib tary - ia? O t aro ! - in '!li cto taI\ 0 Link#5 Normal force at Link#5 IPile I Illustration A.Tributary area for wind force normal to wall (Link#5) '. Solution: The uplift and lateral forces can be determined as follows: Uplift. • Ignore the contribution of the wall's dead load for resistance to uplift because the amount of wall dead load above the header connection is small Uplift load= :(565.2 plf)(header span) =(479 plf)(7 ft)=3,955 lb 2_ (241.9 plf)(header span) _(241.9 plf)(7 ft)- =1,694 lb Lateral load 2. . 9-14 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 Table 10-2.ASTM D2487-10 Soil Classifications,(concluded) Qo = n Major Divisions CD cn Typical Names Classification Criteria Inorganic silts,very ML fine sands, rock Fine- j • I flout,silty or clayey i fine sands grained soils: • Inorganic clays i ! 50% or Silts and clay liquid j of low,to medium more . ,! limit 50% or less CL ; plasticity, gravelly 'passes clays,,sandy clays, - No.200 11 silty clays, lean clays sieve 'I Organic silts and OL organic silty clays of . a low plasticity ( Inorganic silts, • 4 micaceous or Fine- I - MH diatomaceous fine grained `,a sands or silts, elastic soils:: :�l I silts i l 50° ,+ Silts and clay liquid or +( limit greater Inorganic clays of more re . 50% CH high plasticity,fat passes. ,l clays s ' No.200 'i, _.__.__7___.y._.: .___._._. .__.__sieve i Organic clays of !i OH medium to high plasticity -- --------_------ ----..�a. --- Peat, muck, and •Highly organic soils PT other highly organic soils Adapted,with permission,from ASTM D2487-10 Standard Practice for Classification of Soils for Engineering Purposes(Unified Soil Classification System),copyright ASTM International,100 Barr Harbor Drive,West Conshohocken,PA 19428.The complete standard is available at ASTM International,http://www.astm.org. Angle of Internal Friction/Soil Friction Angle: The angle of internal friction is a measure of the soil's ability to resist shear forces without failure. Internal friction depends on soil grain size, grain size distribution, and mineralogy. The angle of internal friction is used in the design of shallow and deep foundations.It is also used to determine the sliding resistance developed between the bottom of a footing and the foundation at the adjacent soil strata via Equation 10.1. The following factors should be considered. The normal force includes only the weight of the building (dead load). Live loads should not be considered. Also, ASD load factors in ASCE 7-10 allow only 60 percent of the dead load of a structure to be considered when resisting sliding forces. Foundation materials exert less normal force on a foundation when submerged, so the submerged weight of all foundation materials below the design stillwater depth should be used. Editions of the IBC contain presumptive coefficients of friction for various soil types(for example,coefficients of friction are contained in Table 1806.2 in the 2009 IBC). Those coefficients can be used in Equation 10.1 by substituting them for the term "tan (gyp)." COASTAL CONSTRUCTION MANUAL I 10-9 10 DESIGNING THE FOUNDATION Volume II Subgrade Modulus nh EQUATION 10.1. SLIDING RESISTANCE The subgrade modulus (nh) is used primarily in the design of pile foundations. It, along with the F=tan(gp)(N) pile properties, determines the depth below grade of the point of fixity (point of zero movement where: and rotation) of a pile under lateral loading. F = resistance to sliding (lb) The inflection point is critical in determining tP = angle of internal friction whether piles are strong enough to resist N = normal force on the footing (lb) bending moments caused by lateral loads on the foundation and the elevated building. The point of fixity is deep for soft soils (low subgrade modulus) and stiff piles and shallow for stiff soils (high subgrade modulus) and flexible piles. Subgrade moduli range from 6 to 150 pounds/cubic inch for soft clays to 800 to 1,400 pounds/cubic inch for dense sandy gravel. See Section 10.5.3 for more information on subgrade modulus. 10.4 Design Process The following are the major steps in foundation analysis and design. O Determine the flood zone that the building site.is in. For a site that spans more than one flood zone (e.g., Zone V and Coastal A Zone, Coastal A Zone and Zone A), design the foundation for the most severe zone (see Chapter 3). E Determine the design flood elevation and design stillwater elevation (see Chapter 8). Determine the projected long- and short-term erosion (see Chapter 8). O Determine the site elevation and determine design stillwater depths (see Chapter 8). O Determine flood loads including breaking wave loads, hydrodynamic loads, flood-borne debris loads, and hydrostatic loads. Buoyancy reduces the weight of all submerged materials, so hydrostatic loads need to be considered on all foundations (see Chapter 8). n Obtain adequate soils data for the site (see Section 10.3.3). Determine maximum scour and erosion depths (see Chapter 8). E: Select foundation type (open/deep, open/shallow, closed/deep, or closed/shallow). Use open/deep foundations in Zone V and Coastal A Zone. Use open/shallow foundations in Coastal A Zone only when scour and erosion depths can be accurately predicted and when the foundation can extend beneath the erosion depths. See Sections 10.2 and 10.3.1. Li Determine the basic wind speed, exposure, and wind pressures (see Chapter 8). Determine live and dead loads and calculate all design loads on the elevated building and on the foundation elements (see Chapter 8). 10-10 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 t-, Determine forces and moments at the top of the foundation elements for all load cases specified in ASCE 7-10. Use load combinations specified in Section 2.3 for strength-based designs or Section 2.4 for stress-based designs.Apply forces and moments to the foundation. [2. Design the foundation to resist all design loads and load combinations when exposed to maximum predicted scour and erosion. 10.5 Pile Foundations Pile foundations are widely used in coastal environments and offer several benefits. Pile foundations are deep and, when properly imbedded, offer resistance to scour and erosion. Piles are often constructed of treated timber, concrete, or steel although other materials are also used. Treated timber piles are readily available and because they are wood, they can be cut, sawn, and drilled with standard construction tools used for wood framing.ASTM D25-99 contains specifications on round timber piles including quality requirements, straightness, lengths and sizes (circumferences and diameters) as well as limitations on checks, shakes, and knots. The National Design Specification for Wood Construction (ANSI/ AF&PA 2005) contains design values for timber piles that meet ASTM D25-99 specifications. Pre-cast (and typically pre-stressed) concrete,piles are not readily available in some areas but offer several benefits over treated timber piles. Generally, they can be fabricated in longer lengths than timber piles. For the same cross section, they are stronger than,timber piles and are not vulnerable to rot or wood-destroying insects.The strength of concrete piles can allow them to be used without grade beams. Foundations without grade beams are less vulnerable to scour than'foundations that rely on grade beams (See Section 10.5.6). Steel piles are generally not used in residential construction but are common in commercial construction. Field connections are relatively straightforward,and since steel can be field drilled and welded,steel-to-wood and steel-to-concrete connections can be readily constructed.ASTM A36/A36M-08 contains specifications for mild (36 kip/square inch) steels in cast or rolled shapes. ASTM standards for other shapes and steels include: E For steel pipe,ASTM A53/A53M-10, Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless (ASTM 2010c) For structural steel tubing,ASTM A500-10, Standard Specification for Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes(ASTM 2010b); and ASTM A501-07, Standard Specification for Hot-Formed Welded and Seamless Carbon Steel Structural Tubing (ASTM 2007) ri For welded and seamless steel pipe piles,ASTM 252-10, Standard Specification for Welded and Seamless Steel Pipe Piles (ASTM 2010d) Fiber-reinforced polymer (FRP) piles are becoming more commonplace in transportation and marine infrastructure but are rarely used in residential applications. However, the usage of FRP piles in residential applications is expected to increase.New construction materials can offer many benefits such as sustainability, durability, and longevity but like any new construction material, the appropriateness of FRP piles should be thoroughly investigated before being used in new applications. Although FRP is not discussed in the COASTAL CONSTRUCTION MANUAL 10-11 10 DESIGNING THE FOUNDATION Volume II i publication, Technical Fact Sheet 1.8, Non-Tradi,ional Building Materials and Systems, in FEMA P-499 provides guidance on using new materials and new systems in coastal environments. Table 10-3 is a summary of the advantages and special considerations for three of the more common pile materials. - Table 10-3.Advantages and Special Considerations of Three Types of Pile Materials Material Advantages Special Considerations • Comparatively low initial cost • Difficult to splice • Readily available in most areas •Subject to eventual decay when in soil • Easy to cut, saw and drill or intermittently submerged in water Wood • Permanently submerged piles resistant to decay •Vulnerable to damage from driving • Relatively easy to drive in soft soil (splitting) •Suitable for friction and end bearing pile •Comparatively low compressive load • Relatively low allowable bending stress •Available in longer lengths than wood piles • High initial cost • Corrosion resistant • Not available in all areas • Can be driven through some types of hard • Difficult to make field adjustments for material connections Concrete •Suitable for friction and end-bearing piles • Because of higher weight, require • Reinforced piles have high bending strength special consideration in high seismic • High bending strength allows taller'or more areas heavily loaded pile foundations to be constructed without grade beams • High resistance to bending •Vulnerable to corrosion • Easy to splice • May be permanently deformed if struck •Available in many lengths, sections and sizes by heavy object Steel •Can be driven through hard subsurface material • High initial cost •Suitable for friction and end-bearing piles •Some difficulty with attaching wood • High bending strength, which allows taller or framing more heavily loaded pile foundations to be constructed without grade beams , The critical aspects of pile foundations include the pile material and size and pile embedment depth. Pile foundations with inadequate embedment do not have the structural capacity to resist sliding and overturning (see Figure 10-2). Inadequate embedment and improperly sized piles greatly increase the probability for structural collapse. However,when properly sized, installed, and braced with adequate embedment into the soil (with consideration for erosion and scour effects), a building's pile foundation performance allows the building to remain standing and intact following a'design flood event (see Figure 10-3). 10.5.1 Compression Capacity of Piles — Resistance to Gravity Loads The compression capacity of piles determines their°ability to resist gravity loads from the elevated structure they support. One source that provides an equation for the compression capacity of piles is the Foundation and Earth Structures,Design Manual 7.2 (USDN 1986).The manual,contains Equation 10.2 for determining i 10-12 COASTAL CONSTRUCTION, MANUAL Volume II DESIGNING THE FOUNDATION 10 Figure 10-2. Near collapse due to insufficient pile 1-— embedment, Hurricane / _ Katrina(Dauphin Island, -' 1,- AL, 2005) ._-.-..-..„.",01.011111114 __-_ --- ____,,.1__ __;rj !,-- t.-c- -.6.-,-.:.A LiI ,ile ;II ..V.' \- 117_ -a-,..,_27,_ I\ \\\'\ \''111\1. '1.1\''. 0 \ \ 010 tilliklm.1 I',"; - 110. °'f0 - - - ti Figure 10-3. Surviving pile foundation, Hurricane Katrina (Dauphin Island,AL, ll E �I�I pia �r1 ____ —_ _: � ii ,.'l IL - Li . -4 s ",7". ss ,I,N4ng q :411_2 - __ -� 1,..,4. � f' � ii a .� i 1� �� ' �� 1l; h Oat,��i'�� c 2 lip 1 .1 I. .' J - 13 -' l`{ _ _ - t - the compression capacity of a single pile when placed in granular (non-cohesive) soils. Design Manual 7.2 also contains methods of determining compression capacity of a pile placed in cohesive soils. The resistance of the pile is the sum of the capacity that results from end bearing and friction. The capacity from end bearing is the first term in Equation 10.2; the capacity from friction is given in the second term. Equation 10.2 gives the ultimate compression capacity of a pile. The allowable capacity(Qaiow) used in ASD depends on a Factor of Safety applied to the ultimate capacity. For ASD, Design Manual 7.2 recommends a Factor of Safety of 3.0; thus, QQllow= Quit/3• I COASTAL CONSTRUCTION MANUAL 1 10-13 10 DESIGNING THE FOUNDATION Volume II EQUATION 10.2. ULTIMATE COMPRESSION CAPACITY OF A SINGLE PILE Quit =PT Nq AT+E KHC PO Ds tan 8 where: Quay = ultimate load capacity in compression (lb) PT = effective vertical stress at pile tip (lb/ft2) N = bearing capacity factor (see Table 10-4) AT = area of pile tip (ft2) KHC = earth pressure in compression '(see Table 10-5) Po = effective vertical stress over thei depth of embedment, D (lb/ft2) 8 = friction angle between pile and:soil (see Table 10-6) s = surface area of pile per unit length (ft) D = depth of embedment (ft) Table 10-4. Bearing Capacity Factors(N ) Parameter Pile Bearing Capacity Factors (d'e rees)(a� .*, I 26 28 30 31 32 33 34 35 36 37 38 39 40 I`w9(dnven pile dispiac ment);` 10 15 21 24 29 35 42 50 62 77 86 120^145 1V {drilled piers)(ba>� ' 5 8 10 12 14 17 21 25 30 38 43 60 72 N9=bearing capacity factor =angle of internal friction (a) Limit ry to 28°if jetting is used (b) When a bailer or grab bucket is used below the groundwater table,calculate end bearing based on q not exceeding 28 degrees. For piers larger than 24 inches in diameter,settlement rather than bearing capacity usually controls the design.For estimating settlement,take 50%of the settlement for an equivalent footing resting on the surface of comparable granular soils. Table 10-5. Earth Pressure Coefficients Pile Type KHC KHT Driven single H piles�; I 0.5—1.0 0.3—0.5 Driven single displacementpile:. J`1.0-1.5 0.6-1.0 Driven single displacement tapered pile: 1.5-2.0 1.0-1.3 Dnven,jetted pile 0.4-0.9 0.3-0.6 f Drilled pile(less than 24 inch diameter) ~ 0.7 0.4 Kip=earth pressure compression coefficient KyT=earth pressure tension coefficient 10-14 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 Table 10-6. Friction Angle Between Soil and Pile(3) Pile Type S t Timber I 3/aco Concrete 3A p _ Steel 20 degrees rp=angle of internal friction 10.5.2 Tension Capacity of Piles The tension capacity of piles determines their ability to resist uplift and overturning loads on the elevated structure. One source that provides pile capacity in tension load is the Design Manual 7.2, which is also a reference on compression capacity. Equation 10.3 determines the tension capacity in a single pile. --)EQUATION 10.3. ULTIMATE TENSION CAPACITY OF A SINGLE PILE Tull =IKHTPoDstanS where: Tint = ultimate load capacity in tension (lb) KHT = earth pressure in tension (see Table 10-5) Po = effective vertical stress over the depth of embedment, D (Ib/ft2) S = friction angle between pile and soil (see Table 10-6) s = surface area of pile per unit length (ft2/ft or ft) D = depth of embedment (ft) Note: With the recommended Factor of Safety of 3.0, the allowable tension capacity, Tallow = Tat/3- The Design Manual 7.2 provides tables to identify bearing capacity factors (N9), earth pressure coefficients (KHc and KHT), and friction angle between pile and soil (S) based on pile type and the angle of internal friction (tp) of the soil. Example 10.1 illustrates compression and tension capacity calculations for a single pile not affected by scour or erosion. Table 10-7 contains example calculations using Equations 10.2 and 10.3 for the allowable compression (gravity loading) and tension (uplift) capacities of wood piles for varying embedments, pile diameters, and installation methods.The table also illustrates;the effect of scour around the pile on the allowable compression and tension loads. Scour (and erosion) reduces pile embedment and therefore pile capacity. For this table, a scour depth of twice the pile diameter (2d) with no generalized erosion is considered. COASTAL CONSTRUCTION MANUAL 10-15 tl 10 DESIGNING THE FOUNDATION Volume II t. a EXAMPLE 10.1. CALCULATION FOR.ALLOWABLE CAPACITIES OF WOOD PILES Given: • Closed end, driven timber pile • Diameter (d) 1 ft • Depth of embedment (D)= 15 ft • Soil density(X)= 65 lb/ft3 !! • Angle of internal friction (co).= 30 KHC= 1:0 (applicable coefficient from Table 10-5) • Earth pressure in tension K 0.6 ((applicable coefficient from Table 10-5 • Bearing capacity factor (Ng)= 21 (applicable coefficient from Table 10-4) • Factor of Safety=.3.0 Find: • - - . . .. .: . .. ,i _ ' . . . .... 1. Allowable tension and compression capacities of wood piles embedded in soil Q = load . a//l / 7('° D = length of pile d =. diameter of pile D P pressure Y = soil density r !. . d =7D • Illustration A Pile schematic and pressure diagram 10-16 i COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 EXAMPLE 10.1. CALCULATION FOR ALLOWABLE CAPACITIES OF WOOD PILES (concluded) Solution for#1: Find the allowable tension and compression capacity of the wood pile embedded in soil as follows: • To determine the resultant pressure from the soil on the pile: 8=.4((p)= 4(30°)=22.5° Po =P =yD=(65 lb/ft3)(15 ft)=.975 lbift2 • Geometrical properties of the pile surfaces upon which pressure from the soil is applied to the pile are: At =(ir)(2 d)2 =(3.14)[(0.5)(1 ft)]2 =0.785 ft2 Po =Pt =yD_(65 lb/ft3)(15 ft)= 975 lb/ft2 Allowable compression capacity: Qu[t =(9751b%ft2)(21)(0.785 ft2)+(1.0)(975 lb/ft2)(tan22.5°)(3.14 ft2/ft)(15 ft) Qzr[c =35,095 lb Quit 35,095 lb =ii,G98lb Q11 = =3 3 Allowable tension capacity: Tint=(0.6)(975 lb/ft2)(tan 22.5°)(3.14 ft2/ft)(15'ft)=11,413 lb T T urf _ 11,413 lb =3,8041b al = 3 3 The purpose of Table 10-7 is to illustrate the effects of varying diameters, depths of embedment, and installation methods on allowable capacities. See Section 10.5.4 for information of installation methods. Example calculations used to determine the values in Table 10-7 are used in Example 10.1. The values in Table 10-7 are not intended to be used for design purposes. COASTAL CONSTRUCTION MANUAL 10-17 10 DESIGNING THE FOUNDATION Volume II Table 10-7.Allowable Compression and Tension of Wood Piles Based on Varying Diameters, Embedments, and Installation Methods Compression (pounds) Tension (pounds) Diameter and Embedment Installation Method No Scour 2d Scour No Scour 2d Scour Driven 11,698 9,406 3,804 2,857 d=12 inches - - - - - ---- -- - D=15 feet Jetted 7,894 6,548 1,902 1,429 Augered 6,990 5,545 2,536 1,905 Driven 18,416 15,560 6,763 5,478 d= 12 inches D=20 feet Jetted 11,652 -_ -_10,081 3,382 2,739 Augered 11,292 9,453 4,509 3,652 Driven 9,004 7,482 3,170 2,505 d=10 inches D=15 feet Jetted 5,834 4,977 1,585 1,252 Augered - 5,470 _ 4,497 2,114 1,670 d=diameter D=depth of embedment 10.5.3 Lateral Capacity of Piles The lateral capacity of piles is dictated by the piles and the pile/soil interface. The ability of the pile to resist lateral loads depends on the pile size and material, the soil properties, and on presence or absence of pile bracing. One of the critical aspects of pile design is the distance between the lateral load application point and the point of fixity of the pile. That distance constitutes a moment arm and governs how much bending moment develops when a pile is exposed to lateral loads. For a foundation to perform adequately, that moment must be resisted by the pile without pile failure. Equation 10.4 determines the distance between the point where the lateral load is applied and the point of fixity for an unbraced pile. Note that in Equation 10.4, "d" is the depth below grade of the point of fixity, not the diameter of the pile. Also, see Figure 10-4 for the deflected shape of a laterally loaded pile. Table 10-8 lists recommended values for nh, modulus of subgrade reaction, for a variety of soils (Bowles 1996). For wood pilings, the depths to points of fixity range from approximately 1 foot in stiff soils to approximately 5 feet in soft soils. The ability of site soils to resist lateral loads is a function of the soil characteristics, their location on the site, and their compressive strength. Chapter 7 of the Timber Pile Design and Construction Manual(Collin 2002) contains methods of determining the lateral resistance of timber piles for both fixed pile head conditions (i.e., piles used with grade beams or pile caps) and free pile head conditions (i.e., piles free to rotate at their top).The manual also contains methods of approximating lateral capacity and predicting pile capacity when detailed soils data are known. 10-18 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 1 0 EQUATION 10.4. LOAD APPLICATION DISTANCE FOR AN UNBRACED PILE L=H+d 12 where: L = distance between the location where the lateral force in applied and the point of fixity(i.e., moment arm) (ft) • i s d = depth from grade to inflection point (inches); d=1.8 — EI nh H = distance above eroded ground surface (including localized scour) where lateral load is applied (ft) Lateral load A A \ Centerline of << I s deflected pile under' horizontal point load L H \ Centerline of � I undeflected pile Eroded ground isurface Table 10-8.Values of nh Modulus of Subgrade Reaction ,, � 't, " n��Modulus of Localized scour Soil Type Subgrade Reaction - Point of fixity (pound/cubic inch) Dense sandy gravel 800 to 1,400 L unbraced length Medium dense coarse sand 600 to 1,200 H height of pile above eroded ground Medium sand 400 to 1,000 surface(including localized scour) Fine to silty fine sand 290 to 700.. . Figure 10-4. Medium clay(wet) 150 to 500 Deflected pile shape for an unbraced pile Soft clay 6 to 150. COASTAL CONSTRUCTION MANUAL 10-19 9 10 DESIGNING THE FOUNDATION Volume II 10.5.4 Pile Installation Methods for installing piles include driving, augering, and jetting. A combination of methods may also be used. For example, piles may be placed in augered holes and then driven to their final depth. Combining installation methods can increase the achievable embedment depth.With increased depths, a pile's resistance to lateral and vertical loads can be increased, and it's vulnerability to scour and erosion will be reduced. t= Driving involves hitting the top of the pile with a pile driver or hammer until the pile reaches the desired depth or it is driven to refusal. Piles can be driven with vibratory hammers.Vibratory hammers generate vertical oscillating movements that reduce the soil stress against the pile and which makes the piles easier to drive. Ultimate load resistance is achieved by a combination of end bearing of the pile and frictional resistance between the pile and the soil.A record of the blow counts from the pile driver can be used with a number of empirical equations to determine capacity. r Augering involves placing the pile into a pre-drilled hole typically made with an auger. The augured hole can be the full diameter of the pile or a smaller diameter than the pile. Pre-drilling is completed to a predetermined depth, which often is adjusted for the soils found on the site. After placing the pile into the pre-drilled hole, the pile is then driven to its:final desired depth or until it reaches refusal. G Jetting is similar to augering but instead of using a soils auger,jetting involves using a jet of water (or air) to remove soils beneath and around the pile Like augering,jetting is used in conjunction with pile driving. Both augering and jetting remove natural, undisturbed soil along the side of the pile. Load resistance for both of these methods is achieved by a combination of end bearing and frictional resistance, although the frictional resistance is much less than that provided by driven piles. Figure 10-5 illustrates the three pile installation methods.Table 10-9 lists advantages and special considerations for each method. Figure 10-5. Pier installation methods Hammer(or vibratory Hammer to Water injected to hammer)drives pile set in place create hole for pile j- Hammer to Augered (set in place hole ,rs tom , w : ? � 4 Driven 1. Augered - Jetted 10-20 i COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 4 Table 10-9.Advantages and Special Considerations of Pile Installation Methods Installation Advantages Special Considerations Method •Well-suited for friction piles • Requires subsurface investigation •Common construction practice • May be difficult to reach terminating soil strata if Driving piles are only driven • Pile capacity can be determined • Difficult to maintain plumb during driving and empirically thus maintain column lines • Economical - -- ------- --_ _____..__ • Minimal driving vibration to adjacent • Requires subsurface investigation structures • Not suitable for highly compressed material •Well-suited for end bearing • Disturbs soil adjacent to pile, thus reducing earth • Augering pressure coefficients KHcand KHTto 40 percent •Visual inspection of some soil stratum of that driven for piles possible •Convenient for low headroom situations • Capacity must be determined by engineering judgment or load test • Easier to maintain column lines • Requires subsurface investigation • Minimal driving vibration to adjacent • Disturbs soil adjacent to pile,thus reducing earth structures pressure coefficients KHc and Kin-to 40 percent Jetting •Well-suited for end bearing piles of that driven for piles • Easier to maintain column lines •Capacity must be determined by engineering judgment or load test KHc=earth pressure compression coefficient KHT=earth pressure tension coefficient 10.5.5 Scour and Erosion Effects on Pile Foundations Coastal homes are often exposed to scour and erosion,and because moving floodwaters cause both scour and erosion, it is rare for an event to produce one and not the other.As Figure 10-6 illustrates, scour and erosion have a cumulative effect on pile foundations. They both reduce piling embedment. Original ground ....ara4gaiii ... 1 .1 - ice I— Ind IA : na ITH I \I 111 I ' w e. ' irT-fin dkscouri >T f'' 49 T7'r\ ' tror7"-1} ErosionI roion and scour ' Figure 10-6. Scour and erosion effects on piling embedment COASTAL CONSTRUCTION MANUAL i 10-21 I 10 DESIGNING THE FOUNDATION Volume II A properly designed pile foundation must include,a consideration of the effects of scour and erosion on the foundation system. Scour washes away soils around the piling, reducing pile embedment, and increases stresses within the pile when the pile is loaded. The reduced embedment can cause the foundation to fail at the pile/soil interface. The increased stresses can cause the pile itself to fracture and fail. Erosion is even more damaging. In addition to reducing pile embedment depths and increasing stresses on piles, erosion increases the flood forces the foundation must resist by increasing the stillwater depth at the foundation that the flood produces. Pile foundations that are adequate to resist flood and wind forces without being undermined by scour and erosion can fail when exposed to even minor amounts of scour and erosion. An example analysis of the effects of scour and erosion on a foundation is provided in Erosion, Scour, and Foundation Design (FEMA 2009a), published as part of Hurricane Ike Recovery Advisories and available at http://www.fema.gov/library/viewRecord.do?id=3539. The structure in the example is a two-story house with 10-foot story heights and a 32-foot by 32-foot foundation. The house is away from the shoreline and elevated 8 feet above grade on 25 square timber piles spaced 8 feet apart. Soils are medium dense sands. The house is subjected to a design wind event with a 130-mph (3-second gust) wind speed and a 4-foot stillwater depth above the uneroded grade, with storm surge and broken waves passing under the elevated building. Lateral wind and flood loads were calculated in accordance with ASCE 7-05. Although the wind loads in ASCE 7-10 vary from ASCE 7-05 somewhat, the results of the analyses do not change significantly. Piles were analyzed under lateral wind and flood loads only; dead, live, and wind uplift loads were neglected. If the neglected loads are included, deeper pile embedment and possibly larger piles than the results of the analysis indicated may be needed.Three timber pile sizes (8-inch square, 10-inch square, and 12-inch square) were evaluated using pre-storm embedment depths of 10 feet, 15 feet, and 20 feet and five erosion and scour conditions (erosion = 0 or 1 foot; scour = 2.0 times the pile diameter to 4.0 times the pile diameter). The results of the analysis are shown in Table 10-10. A shaded cell indicates that the combination of pile size, pre-storm embedment, and erosion/scour does not provide the bending resistance and/or embedment required to resist lateral loads. The reason for foundation failure is indicated in each shaded cell ("P" for failure due to bending and overstress within the pile and "E" for an embedment failure from the pile/soil interaction). "OK" indicates that the bending and foundation embedment criteria are both satisfied by the particular pile size/pile embedment/erosion-scour combination. The key points from the example analysis are as follows: Scour and erosion can cause pile foundations to fail and must be considered when designing pile foundations. Li Failures can result from either overloading the pile itself or from overloading at the pile/soil interface. E. Increasing a pile's embedment depth does not offset a pile with a cross section that is too small or pile material that is too weak. [I Increasing a pile's cross section (or its material strength) does not compensate for inadequate pile embedment. 10-22 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 Table 10-10. Example Analysis of the Effects ofScour and Erosion on a Foundation Pile Diameter(a) Pile Embedment Before Erosion and 8 inches 10 inches 12 inches Erosion and Scour Scour Conditions Reason for Failure Erosion =0, Scour=0 i P, E E OK Erosion = 1 foot, Scour=2.0a . • P,,E E E 10 feet Erosion = 1 foot, Scour=2.5a j • P, E . E :E • . ' Erosion = 1 foot, Scour=3.0a P, E • E E Erosion = 1 foot, Scour=4.0a P,_E P,.E E - Erosion =0, Scour=0 I P OK OK. - Erosion = 1 foot, Scour=2.0a i P OK OK . 15 feet .. Erosion = 1 foot, Scour=2.5a P OK OK Erosion = 1 foot, Scour=3.0a - P: • OK OK Erosion = 1 foot, Scour=4.0a P, E • P, E - E Erosion =0, Scour=0 P OK OK Erosion = 1 foot, Scour=2.0a ; P OK OK • . . 20-feet- - .. Erosion = 1 foot, Scour=2.5a i. P OK OK Erosion = 1 foot, Scour=3.0a P ; OK OK • Erosion = 1 foot, Scour=4.0a P, P OK Two-story house supported on square timber piles and located away from the shoreline,storm surge and broken waves passing under the building,130-mph wind zone,soil=medium dense sand. a=pile diameter E=foundation fails to meet embedment requirements OK=bending and foundation embedment criteria are both satisfied by the particular pile size/pile embedment/erosion-scour combination P=foundation fails to meet bending 10.5.6 Grade Beams for Pile Foundations Piles can be used with or without grade beams or pile caps. Grade beams create resistance to rotation (also called "fixity") at the top of the piles and provide a method to accommodate misalignment in piling placement. When used with grade beams, the piles and foundation elements above the grade beams work together to elevate the structure,provide vertical and lateral support for the elevated home, and transfer loads imposed on the elevated home and the foundation to the ground below. Pile and grade beam foundations should be designed and constructed so that the grade beams act only to provide fixity to the foundation system and not to support the lowest elevated floor. If grade beams support the lowest elevated floor of the home, they become the lowest horizontal structural member and significantly higher flood insurance premiums would result. Grade beams must also be designed to span between adjacent piles, and the piles must be capable of resisting both the weight of the grade beams when undermined by erosion and scour and the loads imposed on them by forces acting on the structure. COASTAL CONSTRUCTION MANUAL 10-23 10 DESIGNING THE FOUNDATION Volume II Pile foundations with grade beams must be constructed with adequate strength to resist all lateral and vertical loads. Failures during Hurricane Katrina often resulted from inadequate connections between the columns and footings or grade beams below (see Figure 10-7). If grade beams are used with wood piles, the potential for rot must be considered when designing the connection between the grade beam and the pile. The connection must not encourage water retention. The maximum bending moment in the piles occurs at the grade beams, and decay caused by water retention at critical points in the piles could induce failure under high-wind or flood forces. While offering some advantages, grade beams can become exposed by moving floodwaters if they are not placed deeply enough. Once exposed, the grade beams create large horizontal obstructions in the flood path that significantly increase scour. Extensive scour was observed after Hurricane Ike in 2008 around scores of homes constructed with grade beams (see Figure 10-8). Although not possible for all piling materials, foundations should be constructed without grade beams whenever possible. For treated timber piles, this can limit elevations to approximately 8 feet above grade. The actual limit depends greatly on flood forces, number of piles, availability of piles long enough to be driven to the required depth and extend above grade enough to adequately elevate the home, and wind speed and geometry of the elevated structure. For steel and concrete piles, foundations without grade beams are practical in many instances, even for taller foundations. Without grade beams to account for pile placement, additional attention is needed for piling alignment, and soils test are needed for design because pile performance depends on the soils present, and presumptive piling capacities may not adequately predict pile performance. Figure 10-7. -- Column connection 0lp1-fir l failure, Hurricane Katrina , (Belle Fontaine Point, - Jackson County, MS, ¢ ` t,: ; a 2005) Yet 1 3 yt t `- ' ,` �• ^ � f "` ' n 10-24 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 flbwNW- I I Fill Figure 10-8. Scour around grade beam, Hurricane Ike(Galveston Island,TX,2008) 10.6 Open/Deep Foundations In this section, some of the more common'types of open/deep foundation styles are discussed. Treated timber pile foundations are discussed in Section 10.6.1, and other types of open/deep pile foundations are discussed in Section 10.6.2. 10.6.1 Treated Timber Pile Foundations In many coastal areas, treated timber piles are the most common type of an open/deep style foundation. Timber piles are the first choice of many builders because they are relatively inexpensive,readily available,and relatively easy to install. The driven timber pile system (see Figure 10-9) is suitable for moderate elevations. Home elevations greater than 10 feet may not be practical because of pile length availability,the pile strength required to resist lateral forces (particularly when considering erosion and scour), and the pile embedment required to resist lateral loads after being undermined by scour and erosion. When used without grade beams, timber piles typically extend from the pile tip to the lowest floor of the elevated structure.With timber piles and wood floor framing, the connection of the elevated structure to the piling is essentially a pinned connection because moment resisting connections in wood framing are difficult to achieve. Pinned connections do not provide fixity and require stronger piles to resist the same loads as piles that benefit from moment resisting connections at their tops. Improved performance can be achieved if the piles extend beyond the lowest floor to the roof(or an upper floor level).Doing so provides resistance to rotation where the pile passes through the first floor.This not only reduces stresses within the piles but also increases the stiffness of the pile foundation and reduces movement under lateral forces. Extending piles in this fashion improves survivability of the building. The timber pile system is vulnerable to flood-borne debris. During a hurricane event, individual piles can be damaged or destroyed by large, floating;debris. Two ways of reducing this vulnerability are (1) using piles with diameters that are larger than those called for in the foundation design and (2) using more piles and continuous beams that can redistribute loads around a damaged pile. Using more piles and continuous beams increases structural redundancy and can improve building performance. COASTAL CONSTRUCTION MANUAL 10-25 10 DESIGNING THE FOUNDATION Volume II II Figure 10-9. Profile of timber pile See FEMA 499 for suggested Continuous pile-to-roof/floor foundation type pile-to-floor framing diaphragm will improve connection details performance r r I Bottom of lowest horizontal structural member 45°maximum 1� ti Two sets of rod Treated timbe% cross-bracing pile ASTM-D25 FEMA P-550, Recommended Residential Construction for Coastal Areas(FEMA 2006), contains a foundation design using driven timber piles. The foundation design is based on presumptive piling capacities that should be verified prior to construction. Also, the design is intended to support an elevated building with a wide range of widths and roof slopes and as such contains some inherent conservatism in the design. Design professionals who develop foundation designs for specific buildings and have site information on subsurface conditions can augment the FEMA P-550 design to provide more efficient designs that reduce construction costs. 10.6.1.1 Wood Pile-to-Beam Connections In pile foundations that support wood-framed structures,systems of perimeter and interior beams are needed to support the floors and walls above. Beams must be sized to support gravity loads and, in segmented shear wall construction, resist reactions from shear wall segments. To transfer those loads to the foundation,wood piles are often notched to provide a bearing surface for the beams. Notches should not reduce the pile cross section by more than 50 percent (such information is typically provided by a design professional on contract documents). For proper transfer of gravity loads, beams should bear on the surface of the pile notch. 10-26 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 Although connections play an integral role in the design of structures, they are typically regarded as the weakest link. Guidance for typical wood-pile to wood-girder connections can be found in Fact Sheet 3.3, Wood Pile to Beam Connections, in FEMA P-499. 10.6.1.2 Pile Bracing When timber piles with a sufficiently large cross section are not available, timber piles may require bracing to resist lateral loads. Bracing increases the lateral stiffness of a pile foundation system so that less sway is felt under normal service loads. Bracing also lowers the location where lateral forces are applied to individual piles and reduces bending stresses in the pile. When bracing is used, the forces from moving floodwaters and from flood-borne debris that impacts the braces should be considered. • Bracing is typically provided by diagonal bracing or knee bracing. Diagonal bracing is more effective NOTE from a structural standpoint, but because diagonal Fact Sheet 3.2, Pile Installation, in FEMA bracing extends lower into floodwaters, it is more P-499 recommends that pile bracing be likely to be damaged by flood-borne debris. It used only for reducing the structure's can also trap flood-borne debris, and trapped sway and vibration for comfort. In other flood-borne debris increases flood forces on the words, bracing should be used to address foundation. serviceability issues and not strength issues. The foundation design should consider the Knee bracing does not extend as deeply into piles as being unbraced as the condition that floodwaters as cross bracing and is less likely to be may occur when floating debris removes or affected by flood-borne debris but is less effective damages the bracing. If the pile foundation is not able to provide the desired strength at reducing stresses in the pile and also typically performance without bracing, the designer requires much stronger connections to achieve ' should consider increasing the pile size. similar structural performance as full-length cross .a_ bracing. Diagonal Bracing Diagonal bracing often consists of dimensional lumber that is nailed or bolted to the wood piles. Steel rod bracing and wire rope (cable) bracing can also be used. Steel rod bracing and cable bracing have the benefit of being able to use tensioning devices, such as turnbuckles, which allow the tension of the bracing to be maintained. Cable bracing has an additional benefit in that the cables can be wrapped around pilings without having to rely on bolted connections, and wrapped connections can transfer greater loads than bolted connections. Figure 10-10 shows an example of diagonal bracing using dimensional lumber. Diagonal braces tend to be slender, and slender braces are vulnerable to compression buckling. Most bracing is therefore considered tension-only bracing. Because wind and flood loads can act in opposite directions, tension-only bracing must be installed in pairs. One set of braces resists loads from one direction, and the second set resists loads from the opposite direction. Figure 10-11 shows how tension-only bracing pairs resist lateral loads on a home. The placement of the lower bolted connection of the diagonal brace to the pile requires some judgment. If the connection is too far above grade, the pile length below the connection is not braced and the overall foundation system is less strong and stiff. COASTAL CONSTRUCTION MANUAL 10-27 10 DESIGNING THE FOUNDATION Volume II Figure 10-10. �� ir\ Diagonal bracing using t El®; I t ; , dimensional lumber •.�.�,; -i _ '��' 1111 ■._ ■ilk_ I I. --:.-_„.:,_ III Illi ;;;;:.:1.4.'14 ,:,4 I III' '�*'r•� `II II r .-,. ./r/ Ilk .�- ES c. ti LI :w.� '�� .� v. 5 aartzlI fiaffG�C'-Q NOTE Typical \ F Lateral force brace airs p >" T Tension C Compression 1i Ii I. 1i 11 II II . II i :11 II II I, 1, i 11 I, II II .. II I 11 _ F F amimil 1 .- j 11 II II1 IIi fI 1 LI 1 11 II 11 II 11 II 11 II II 11 - II 11 11 11 II For slender braces and cable braces, • Forces in opposite direction braces loaded in compression should bring opposite braces into play not be considered effective Figure 10-11. Diagonal bracing schematic 10-28 II COASTAL CONSTRUCTION MANUAL 8 Volume II DESIGNING THE FOUNDATION 10 p P. _ _ - _ X,jai - EXAMPLE :10.2: DIAGONAL BRACE FORCE Given::. • Lateral load= 989 lb Brace angle= 45. Find: - 1. Tension force in the diagonal brace in Illustration A. is Floor support beam i E 9891b V 945 i . Pile 90°It . . 45° • Ground < I' 9.33ft ) I • Pile spacing Unbraced . .. • : length - Point of fixity w . IllustrationA. Force diagram for diagonal bracing :Solution for'#1: The tension force in the'diagonal brace can be found as follows: Rod bracing is used and assumed to act intension only because of the rigidity of the rod brace in.tension and lack of stiffness of the rod in compression.. The tension brace force is calculated as follows: 989 lb diagonal= _cos.45o =1,399 lb . Interaction of the soil and the pile should be checked to ensure that the uplift component of the brace force i. can be resisted: I' I . , COASTAL CONSTRUCTION MANUAL ' 10-29 10 DESIGNING THE FOUNDATION Volume II For timber piles, if the connection is too close to grade, the bolt hole is more likely to be flooded and subject to decay or termite infestation, NOTE which can weaken the pile at a vulnerable location.All bolt holes should Bolt holes in timber piles be treated with preservative after drilling and prior to bolt placement. should be field-treated (see Chapter 11). Knee Bracing - ,,, Knee braces involve installing short diagonal braces between the upper portions of the pilings and the floor system of the elevated structure (see Figure 10-12). The braces increase the stiffness of an elevated pile foundation and can contribute to resisting lateral forces.Although knee braces do not stiffen a foundation as much as diagonal bracing, they offer some advantages over diagonal braces. For example, knee braces present less obstruction to waves and debris,are shorter and less prone to compression buckling than diagonal braces, and may be designed for both tension and compression loads. The entire load path into and through the knee brace must be designed.The connections at each end of each knee brace must have sufficient capacity to handle both tension and compression and to resist axial loads in the brace. The brace itself must have sufficient cross-sectional area to resist compression and tensile loads. Figure 10-12. K Knee bracing • 1 10-30 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 The feasibility of knee bracing is often governed by the ability to construct strong connections in the braces that connect the wood piles to the elevated structure. 10.6.1.3 Timber Pile Treatment Although timber piles are chemically treated to resist rot and damage from insects, they can be vulnerable to wood-destroying organisms such as fungi and insects if the piles are subject to both wetted and dry conditions. If the piles are constantly submerged, fungal growth and insect colonies cannot be sustained; if only periodically submerged, conditions exist that are sufficient to sustain wood-destroying organisms.Local design professionals familiar with the performance of driven, treated timber piles can help quantify the risk. Grade beams can be constructed at greater depths or alternative pile materials can be selected if damage from wood-destroying organisms is a major concern. Cutting, drilling, and notching treated timber piles disturb portions of the piles that have been treated for rot and insect damage. Because pressure-preservative-treated piles, timbers, and lumber are used for many purposes in coastal construction, the interior, untreated parts of the wood can be exposed to possible decay and infestation. Although treatments applied in the field are much less effective than factory treatments, the potential for decay can be minimized with field treatments. AWPA M4-06 describes field treatment procedures and field cutting restrictions for poles, piles, and sawn lumber. Field application of preservatives should be done in accordance with the instructions on the label, but if instructions are not provided, dip soaking for at least 3 minutes is considered effective. When dip soaking for 3 minutes is impractical, treatment can be accomplished by thoroughly brushing or spraying the exposed area.The preservative is absorbed better at the end of a member or end grains than on the sides or side grains. To safeguard against decay in bored holes, the preservative should be poured into the holes. If the hole passes through a check (such as a shrinkage crack caused by drying), the hole should be brushed; otherwise, the preservative will run into the check instead of saturating the hole. Copper naphthenate is the most widely used preservative for field treatment. Its color (deep green) may be objectionable aesthetically, but the wood can be painted with alkyd paints after extended drying. Zinc naphthenate is a clear alternative to copper naphthenate but is not as effective in preventing insect infestation and should not be painted with latex paints. Tributyltin oxide is available but should not be used in or near marine environments because the leachates are toxic to aquatic organisms. Sodium borate is also available, but it does not readily penetrate dry wood and rapidly leaches out when water is present. Sodium borate is therefore not recommended. Waterborne arsenicals, pentachlorophenol, and creosote are unacceptable for field applications. 10.6.2 Other Open/Deep Pile Foundation Styles Several other styles of pile foundations, in addition to treated timber piles, are used although their use often varies geographically depending on the availability of materials and trained contractors. FEMA P-550 contains foundation designs that use deep, driven steel and treated timber piles and grade beams that support a system of concrete columns. The second edition of FEMA P-550 (FEMA 2006) added a new design for treated timber piles that incorporates elevated reinforced beams constructed on the concrete columns. In the new design, the elevated beams work with the columns and grade beams to create reinforced concrete portal frames that assist in resisting lateral loads.The elevated beams also create a suitable platform COASTAL CONSTRUCTION MANUAL 10-31 10 DESIGNING THE FOUNDATION Volume II that can support a home designed to a prescriptive standard such as Wood Framed Construction Manual for One-and Two-Family Dwellings (AF&PA 2012) or ICC 600-2008. Figure 10-13 shows one of the deep pile foundation systems that uses treated timber piles and grade beams. The steel pipe pile and grade beam foundation system contained in FEMA P-550 is similar but requires fewer piles because the higher presumptive strength of the steel piles compared to the timber piles. Figure 10-14 shows the foundation system added in the Second Edition of FEMA P-550 (FEMA 2009b), which incorporates an elevated concrete beam. Figure 10-13. Floor of elevated Section view of a steel building pipe pile with concrete column and grade beam foundation type DEVELOPED FROM FEMA P-550,CASE B E=1� 1111 Reinforced Bottom of lowest concrete column horizontal structural 1111 member 111 Shear reinforcement Longitudinal reinforcement Reinforced concrete grade beam \\/ %�\ \\f 10-32 COASTAL CONSTRUCTION :MANUAL Volume II DESIGNING THE FOUNDATION 10 I Figure 10-14. Section view of a r�� -- Reinforced foundation constructed I[IIIIIicuir concrete beam with reinforced concrete A beams and columns to IN create portal frames MN Bottom of lowest horizontal Reinforced 0 structural member SOURCE:ADAPTED FROM FEMA P-550,SECOND concrete column llllllll— EDITION,CASE H N II/MI -7Longitudinal reinforcement - I - 7 f Shear reinforement Y\\ \\ _,--- ` l--I !. f < ` Reinforced i I concrete grade �\�j\ — a _ _I i •I _ _ beat. Tension connection I Steel pipe pile The grade beams that are shown in Figures 10-13 and 10-14 should not be used as structural support for a concrete slab that is below an elevated building in Zone V.Although a concrete slab may serve as the floor of a ground-level enclosure (usable only for parking, storage, or building access), the slab must be independent of the building foundation. If a grade beam is used to support the slab, the slab becomes the lowest floor of the building, the beam becomes the lowest horizontal structural member supporting the lowest floor, and the bottom of the beam becomes the reference elevation for flood insurance purposes. For buildings in Zone V, the NFIP, IBC and IRC require that the lowest floor elevated to or above the BFE be supported by the bottom of the lowest horizontal structural member. Keeping the slab from being considered the lowest floor requires keeping the slab and grade beams separate, which means the slab and grade beams cannot be monolithic or connected by reinforcing steel or other means. Like the driven, treated pile foundation discussed in Section 10.6.1, the foundation designs discussed in this section are based on presumptive piling capacities that should be verified prior to construction. Also, design professionals who develop foundations designs for specific buildings and have site information on subsurface conditions can augment the FEMA P-550 design to provide more efficient designs that reduce construction costs. COASTAL CONSTRUCTION MANUAL 10-33 i 10 DESIGNING THE FOUNDATION Volume II 10.7 Open/Shallow Foundations Open/shallow foundations are recommended for areas that are exposed to moving floodwaters and moderate wave actions but are not exposed to scour and erosion,which can undermine shallow footings. Open/shallow foundations are recommended for some riverine areas where an open foundation style is desirable and for buildings in Coastal A Zone where scour and erosion is limited. In Coastal A Zones where the predicted scour and erosion depths extend below the achievable depth of shallow footings and in Coastal A Zone where scour and erosion potential is unknown or cannot be accurately predicted, open/deep foundations should be installed. FEMA P-550 contains designs for open shallow foundations. The foundations are resistant to moving floodwaters and wave action, but because they are founded on shallow soils, they can be vulnerable to scour and erosion. Figure 10-15. Profile of an open/ Floor framing of shallow foundation elevated building SOURCE:ADAPTED FROM FEMA P-550,CASE D Bottom of lowest horizontal structural member Reinforced n Longitudinal concrete column reinforcement A. Shear reinforcement 1111 1111 Ial I■1I 1■■l 11111 Iui \/\\ \ �\\\i�\\j\\ Reinforced concrete i '4 10-34 COASTAL CONSTRUCTION: MANUAL Volume II DESIGNING THE FOUNDATION 10 The FEMA P-550 designs make use of a rigid mat to resist lateral forces and overturning moment. Frictional resistance between the grade beams and the supporting soils resist lateral loads.The weight of the foundation and the elevated structure resist uplift forces. Because the foundation lacks the uplift resistance provided by piles, foundation elements often need to be relatively large to provide sufficient dead load to resist uplift, particularly when they are submerged. Grade beams need to be continuous because, as is shown in Section 10.9, discrete foundations that have sufficient capacity to resist lateral and uplift forces without overturning are difficult to design. FEMA P-550 contains two types of open/shallow foundations. The foundation type shown in Figure 10-15 uses a matrix of grade beams and concrete columns to elevate the building. The grade beam shown in Figure 10-15 should not be used as structural support for a concrete slab that is below an elevated building in Zone V. If the grade beam is used to support the slab, the slab will be considered the lowest floor of the building, which will lead to the insurance ramifications described in Section 10.6.2. When used to support wood framing, the columns of open/shallow foundations are typically designed as cantilevered beam/columns subjected to lateral forces, gravity forces and uplift forces from the elevated structure and flood forces on the foundation columns. Because of the inherent difficulty of creating moment connections with wood framing, the connections between the top of the columns and the bottom of the elevated structure are typically considered pinned. Maximum shear and moment occurs at the bottom of the columns, and proper reinforcement and detailing is needed in these areas. Also, because there are typically construction joints between the tops of the grade beams and the bases of the columns where salt-laden water can seep into the joints, special detailing is needed to prevent corrosion. Designing an open/shallow foundation that uses concrete columns and elevated concrete beams can create a frame action that increases the foundation's ability to resist lateral loads. This design accomplishes two things. First, the frame action reduces the size of the columns and in turn reduces flood loads on them, and second,when properly designed, the elevated'beams act like the tops of a perimeter foundation wall. Homes constructed to one of the designs contained in prescriptive codes can be attached to the elevated concrete beams with minimal custom design. Unlike deep,driven-pile foundations, both types of open/shallow foundations can be undermined by erosion and scour. Neither foundation type should:be used where erosion or scour is anticipated to expose the grade beam. 10.8 Closed/Shallow Foundations Closed/shallow foundations are similar to the foundations that are used in non-coastal areas where flood forces are limited to slowly rising floods with no wave action and only limited flood velocities. In those areas, conventional foundation designs, many of which are included for residential construction in prescriptive codes and standards such as the 2012 IRC and ICC 600-2008, may be used. However, these codes and standards do not take into account forces from moving floodwaters and short breaking waves that can exist inland of Coastal A Zones. Therefore, caution should be used when using prescribed foundation designs in areas exposed to moving floodwaters and breaking waves. FEMA P-550 contains two foundation designs for closed/shallow foundations: a stem wall foundation and a crawlspace foundation. Crawlspace foundation walls in SFHAs must be equipped with flood vents COASTAL CONSTRUCTION MANUAL 10-35 tl 10 DESIGNING THE FOUNDATION Volume II to equalize hydrostatic pressures on either side of,;the wall. See FEMA Technical Bulletin 1, Openings in Foundation Walls and Walls of Enclosures (FEMA 2008c). However, the flood vents do not significantly reduce hydrodynamic loads or breaking wave loads, and even with flood vents, flood forces in Coastal A Zones can damage or destroy these foundation styles. Both closed/shallow foundations contained in FEMA P-550 are similar to foundations found in prescriptive codes but contain the additional reinforcement requirement to resist moving floodwaters and short (approximately 1.5-foot)breaking waves.Figure 10-16 shows the stem wall foundation design in FEMA P-550. Figure 10-16. Stem wall foundation Extend reinforcing steel design into slab for laterally supported walls SOURCE:ADAPTED FROM FEMA P-550,CASE F —fu /// /\ / / y Iillr\\//\\//\\//\\//\�' 15414/ srN • 10.9 Pier Foundations Properly designed pier foundations offer the following benefits: (1) their open nature reduces the loads they must resist from moving floodwaters, (2) taller piers can often be constructed to provide additional protection without requiring a lot more reinforcement, and (3) the piers can be constructed with reinforced concrete and masonry materials commonly used in residential construction. Pier foundations, however, can have drawbacks. If not properly designed and constructed, pier foundations lack the required strength and stability to resist loads'from flood,wind or seismic events.Many pier foundation failures occurred when Hurricane Katrina struck the Gulf Coast in 2005. The type of footing used in pier foundations greatly affects the foundation's performance (see Figure 10-17). When exposed to lateral loads, discrete footings can rotate so piers placed on discrete footings are suitable 10-36 COASTAL CONSTRUCTION MANUAL ApP Volume II DESIGNING THE FOUNDATION 10 _ ; Figure 10-17. Performance comparison '' � ' of pier foundations: piers on discrete footings '!^-• (foreground)failed by 'e rotating and overturning - while piers on more ' ii substantial footings (in } 4- this case a concrete c mat) survived Hurricane e 4- -0 0- 4 . Katrina (Pass Christian, ' ,_ ;� MS, 2005) w �; P.. mot• ,?` ,'1-,'Y -ie- - only when wind and flood loads are relatively low. Piers placed on continuous concrete grade beams or concrete footings provide much greater resistance to lateral loads and are much less prone to failure. Footings and grade beams must be reinforced to resist the moment forces that develop at the base of the piers from the lateral loads on the foundation and the elevated home. Like other open/shallow foundations, pier foundations are appropriate only where there is limited potential for erosion or scour. The maximum estimated depth for long- and short-term erosion and localized scour should not extend below the bottom of the footing or grade beam. In addition, adequate resistance to lateral loads is often difficult to achieve for common pier sizes on continuous footings. Even for relatively small lateral loads, larger piers designed as shear walls are often necessary to provide adequate resistance. The following section provides an analysis of a pier foundation on discrete concrete footings. The analysis shows that discrete pier footings that must resist lateral loads are typically not practical. 10.9.1 Pier Foundation Design Examples The following three examples discuss pier foundation design. Example 10.3 provides an analysis of the pier footing under gravity loads only (see Figure 10-18) and the footing size required to ensure that the allowable soil bearing pressure is not exceeded. Example 10.4 provides a consideration of uplift forces that many footings (see Figure 10-19) must resist to prevent failure during a design wind event. The analysis in Example 10.4 assumes that other foundation elements are in place to resist the lateral loads that must accompany uplift forces. Example 10.5 adds lateral loads to the pier and footing (see Figure 10-20) to model buildings that lack continuous foundation walls or other lateral load resisting features. The lateral loads can result from wind, seismic or moving floodwaters. COASTAL CONSTRUCTION MANUAL 10-37 10 DESIGNING THE FOUNDATION Volume II Figure 10-18. IPier foundation and spread footing under A I gravity loading h Column/pier x P v Croat : _. Footing ( L NOTE Pa axial force x length below L footing dimension grade tfaat footing thickness hear height of pier above grade Pw A h./ Column/pier x , t � tf„at Footing .: NOTE P Uplift force L Footing dimension tfot Footing thickness Figure 10-19. x Length below grade Pier foundation and hcal Height of pier above grade spread footing exposed to uplift forces 10-38 COASTAL CONSTRUCTIONI MANUAL Volume II DESIGNING THE FOUNDATION 10 i P Figure 10-20. w Pier foundation and E P, spread footing exposed to uplift and lateral forces \ hoar Column/pier Deflected \, `\�, position \\ \ \ V , I, tjj, }1111 '':- .. ii L x.l NOTE Pw uplift force hcol height of pier L footing dimension above grade too, footing thickness Pi lateral force x length below grade R reaction force e eccentricity 1 Several equations exist for designing discrete footings exposed to gravity loads only. Equation 10.5, which models the weight of the footing by reducing,the allowable bearing capacity of the soils by the weight of the footing, is used for Example 10-3. Equation 10.5 considers the weight of the pier and footing, the gravity load imposed on the top of the pier, and the allowable soil bearing capacity of the soils to determine footing dimensions. The equation provides the length (L) of a square footing. The equation can be modified for rectangular footings of a given aspect ratio /3 (ratio of width to length) and including/3 in the denominator of the term to the right of the equals sign. Equation 10.5 assumes that the gravity load is equally distributed across the bottom surface of the footing and the soil stresses are constant. This condition is appropriate when the gravity loads are applied at the center of the pier (and the pier is centered on.the footing) and when no lateral loads are applied. The foundation system must have sufficient weight to prevent failure when uplift loads are applied.ASCE 7-10 requires the designer to consider only 60 percent of the dead load when designing for uplift (ASD load combination#7). If the foundation is located in an SFHA, portions of it will be located below the stillwater elevation and will be submerged during a design event. The dead load of a material is less when submerged so the submerged weight must be considered (see Section 8.5.7). In Example 10.4, it is assumed that the stillwater depth at the site is 2 feet. COASTAL CONSTRUCTION MANUAL 10-39 n ' i 10 DESIGNING THE FOUNDATION Volume II EQUATION 10.5. DETERMINATION OF SQUARE FOOTING SIZE FOR GRAVITY LOADS 0.5 Pa+(hcol +x—t foot)Wcol tcol we L= q—tfootwc where: L = square footing dimension (ft) = gravity load on pier (lb) hcol = height of pier above grade (ft) x = distance from grade to bottom of footing (ft) Wol = column width (ft) tcol = column thickness (ft) w, = unit weight of column and footing material (1b/ft3) q = soil bearing pressure (psf) typo, = footing thickness (ft) �tp EXAMPLE 10.3. PIER FOOTING UNDER GRAVITY LOAD Given: • Figure 10-18 • Gravity load on pier (Pa) = 2,880 lb (includes roof live load, live load, and dead load) • Height of pier above grade (head = 4 ft • Distance from grade to bottom of footing (x) = 2 ft • Column width (Wcol) = 1.33 ft • Column thickness (tool) = 1.33 ft • Unit weight of column and footing material (we) = 150 lb/ft3 • Soil bearing pressure (q) = 2,000 psf • Footing thickness (tfoot) = 1 ft • Home is 24 ft x 30 ft consisting of a matrix of 30 16-in. square piers (see Illustration A) • Piers spaced 6 ft o.c. (see Illustration A) 10-40 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 EXAMPLE 10.3. PIER FOOTING UNDER GRAVITY LOAD (concluded).,:, Pw i A i ':-.:?,'Is, ,ter `. T ' T ' , n` 7' r7 is Af L'. 7 r`� "r t , t at �+ �'`t a; _=� z,w� Jf't LNFf�tjx�k,.�.c I ^.}.� _ u-D9 ti emo Q . o o Q� 'r � © Pi 7-7 lit O , 0 NOTE I I I P, lateral force ( - l Q -/O / 0 /_,0� Pw uplift force I (/ I i Illustration A.Site layout ' " Find: The appropriate square footing sizefor the given gravity load. Solution: The square footing size can be found using Equation 10.5: . 0.5 Pa+(hcol -f-x—t fool) al tcol we L q-tfootwc . L_ 2,880 lb+(4 ft+2 ft=1 ft)(1!.33:ft)(1.33 ft)(150 lb/ft3) os 2,000 psf—(1 ft)(150 lb/ft3) . L= 1:5ft The IRC requires a minimum of 2-in. projection for spread footing. Moving to the next minimum standard footing size, a 24-in..k 24-in.':x 12-in. square footing to resist the,gravity loads should. be used: Example 10.3 and Example 10.4 model the conditions where the pier and footing only resist axial loads that create no moment on the footing. In those states, the soils are equally loaded across the footing.When a pier and footing foundation must resist lateral loads (or must resist gravity loads applied at some distance A from the centroid of the pier), the footing must resist applied moments, and soils below the footing are no longer stressed equally. Soils on one side of the footing experience compressive stresses that are greater than the average compressive stress;soils on the opposite side of the footing experience stresses lower than the average. COASTAL CONSTRUCTION MANUAL 10-41 1 10 DESIGNING THE FOUNDATION Volume II GIs' EXAMPLE 10.4. PIER FOOTING UNDER UPLIFT LOAD. Given:. • Figure 10-19 • Stillwater flood depth (d5),= 2 ft • Density of water (pwater) = 64 lb/ft3 • Uplift load on pier (Pw) = 2,514 lb • Height of pier above grade (hcol) =4 ft • Distance from grade to bottom of footing (x) = 2 ft • Column width ([ col) = 1.33 ft • Column thickness(tcol) = 1.33 ft • Unit weight of column and footing material (we) =.150 lb/ft3 • Soil bearing pressure (q) = 2,000 psf . • Footing thickness (t foo) = 1 ft • Home is 24 ft x 30 ft consisting of a matrix of 30 16-in. square piers (see Example 10.4, Illustration A) • Piers spaced 6 ft. on center (see Illustration,A) Find: The appropriate square footing size for the given uplift loads. Solution: The square footing size can be found as follows: First consider the dead load of submerged portion of column DL,ubme ged —(wc—Pwater)(z+ds—t foot)(Weo1)(tcol) DLtubmerged =(150 lb/ft3 —64 lb/ft3)(2 ft+2 ft—1 ft)(1.33 ft)(1.33 ft)=459.lb Then consider the dead load of portion of column above the stillwater level DLabove —(wc)(hcol —dx)(Wco1)(tcol) DLabove =(150 lb/ft3)(4 ft--2 ft)(1.33 ft)(1.33 ft)=533 lb Total column dead load can then be found DLTotal =DLsubmerged +DLabove =992 lb The footing, when submerged, must provide sufficient weight to resist the deficit of the column dead load. The submerged footing dead load required is given;by the following equation: 10-42 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 EXAMPLE 10.4. PIER FOOTING UNDER UPLIFT LOAD (concluded) Submerged footing dead load = 1 {./3 —0.6(DLrotar)]=1[2,514 lb—0.6(992 lb)]=3,198 lb 0.6 0.6 Footing volume required= 3,1981b =37.0 ft3 (150 lb/ft3 —64 lb/ft3) For a 12-inch-thick footing, the footing area = 37 ft2 The analysis shows that a square, 6 ft by 6 ft by 12 in.,submerged concrete footing and a 5-ft tall, 16-in. square, partially submerged concrete column are required to resist 2,514 lb of uplift. Increasing the footing thickness to 2 ft would allow the footing dimensions to be reduced to 4 ft 6 in. At some value of lateral load or eccentricity, the compressive stresses on one side of the footing go to zero. Because there are no tensile connections between the footing and the supporting soils, the footing becomes unstable at that point and can fail by rotation. Failure can also occur when the bearing strength on the other side of the footing is exceeded. Equation 10.6 relates soil bearing pressure to axial load, lateral load,and footing dimension. For a given axial load, lateral load, and footing dimension, the equation can be used to solve for the maximum and minimum soil bearing pressures, q on each edge of the footing. The maximum can be compared to the allowable soil bearing pressure to determine whether the soils will be overstressed.The minimum stress determines whether instability occurs. Both maximum and minimum stresses are used to determine footing size. Alternatively, for a given allowable soil bearing pressure, axial load, and lateral load, the equation can be solved for the minimum footing size. di EQUATION 10.6. DETERMINATION OF SOIL PRESSURE q= L +6M where: q = minimum and maximum soil bearing pressures at the edges of the footing (lb/ft2) Pt = total vertical load for the load combination being analyzed M = applied moment Pi(hco1+x) (ft lbs) where x and heo1 are as defined previously and Pi is the lateral load applied at the top of the column When designing a pier and footing, P,and Pi depend on the load combination being analyzed. COASTAL CONSTRUCTION MANUAL 10-43 10 DESIGNING THE FOUNDATION Volume II - EXAMPLE 10.5..PIER FOOTING UNDER UPLIFT AND LATERAL LOADS Given: , Figure 10-20 • • Stillwater flood depth (di)_= 2 ft • • Lateral load on pier (P1) = 246 lb (from design example in Chapter 9: (205 plf)/6 ft times 5 piers assumed to be resisting this force) • Uplift-load on pier (Pw) =2,514 lb (derived from 4,19 psf from Chapter 9 times 6 ft) • - • Height of pier-above grade (ht.o1) =4 ft . • • • Distance from grade to bottom of footing (x) = 2 ft • • Column width (W o1) 1.33 ft • -• Column thickness (tcol) = 1.33 ft . • . • Unit weight of column and-footing material.(wc) =:150 lb/ft2 • Soil bearing pressure (q) = 2,000 psf • • .Footing thickness (tfoot) = 1 ft . . .' • • Home is 24 ft x 30 ft consisting of a matrix of 30 16-in:square piers (see Example 10.3, Illustration A) • .• Piers spaced 6 ft o.c. (see Illustration A) ' Find: The appropriate square footing size for the given uplift and lateral loads.. • ' Solution: The square footing size can be found using Equation 10.6: '_ : : • -'For simplicity,.this example assumes the pier is.partiallysubinerged and exposed to uplift forces,(as in Example 10.4)'but that there are no loads from moving floodwaters or wave action. In an actual design, those'forces would need to be considered.Also, if the vertical load is applied at an eccentricity"A", the . .moment PA must be combined with P1(H+ x) (by vector addition) to determine the.total moment applied_to-the footing.2 • . . The.total induced moment at the footing can be modeled by considering an 'effective reaction R • numerically equal'to the total vertical load Pt but applied at an eccentricity e.from the centroid'of the footing. The lateral load is modeled at the centroid of the footing where it contributes only to sliding. - .The equivalent eccentricity e is given by the following formula: • 2 Unless the eccentricity from the lateral loads is'collinear with the eccentricity from the vertical loads,the footing will be - - exposed to biaxial bending.For biaxial bending,soil stresses must be checked'in both directions.' 10-44 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10 0 , EXAMPLE 10.5. PIER FOOTING UNDER UPLIFT AND LATERAL LOADS (concluded) EQUATION A e= P (see Figure 10-20) where: e = eccentricity Pt = total vertical load for the load combination being analyzed M = applied moment Pi(II+x) (ft-lbs) where x and H are as defined previously Pi is the lateral load applied at the top of the column. For equilibrium, R must be applied within the "kern"of the footing (for a square footing, the kern is a square with dimension of L/3'centered about the centroid of the footing). Mathematically, e cannot exceed.L/6. Ensuring that the reaction R is applied within the kern of the footing prevents tensile stresses from forming on the edge of the footing. Calculating the minimum soils stress for;various footing widths (using a recursive solution) shows that the footing would need to be 11 ft 4 in.wide to prevent overturning. Increasing the footing i. thickness to 2 feet would allow the footing size to be reduced to approximately 8 ft 9 in. Either design is not practical to construct. 10.9.2 Pier Foundation Summary These analyses indicate that piers with discrete footings are practical to construct when they are required to resist gravity loads only but are not practical'when they must resist uplift forces or lateral loads. Although prescriptive designs for pier foundations are available in some codes and standards, users of the codes and standards should ensure that the designs take into account all of the loads the foundations must resist. Prescriptive designs should only be used to resist lateral and uplift loads after they have been confirmed to be adequate. Constructing piers on continuous footings makes pier foundations much more resistant to coastal hazards, but prescriptive designs for piers on continuous footings are not present in widely adopted codes such as the IRC and IBC. Until prescriptive designs'using piers are developed, these styles of foundations should be engineered. Continuous footings are discussed in Section 11.1.5 of FEMA 549, Hurricane Katrina in the Gulf Coast(FEMA 2006), and continuous footing designs that can be used for the basis of engineered foundations are contained in FEMA P-550. I COASTAL CONSTRUCTION MANUAL ; 10-45 10 DESIGNING THE FOUNDATION Volume II 10.10 References ACI (American Concrete Institute). 2008. Building!Code Requirements for Structural Concrete and Commentary,ACI 318-08. ACI ASCE (American Society of Civil Engineer/TMS (The Masonry Society). 2008. Building Code Requirements and Specifications for Masonry Structures and Related Commentaries, ACI 530-08. AF&PA (American Forest &Paper Association). 2012. Wood Frame Construction Manual for One-and Two-Family Dwellings. Washington, D.C. ANSI (American National Standards Institute) /AF&PA. 2005. National Design Specification for Wood Construction. ASTM (American Society for Testing and Materials). 2005. Standard Specification for Round Timber Piles, ASTM D25-99. ASTM. 2007. Standard Specification for Hot-Formed Welded and Seamless Carbon Steel Structural Tubing. ASTM A501-07. ASTM. 2008. Standard Specification for Carbon Structural Steel. ASTM A36/A36M-08. ASTM. 2009. Standard Practice for Description and Identification of Soils (Visual-Manual Procedure). ASTM D2488-09a. ASTM. 2010a. Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System). ASTM D2487-10. ASTM. 2010b. Standard Specification for Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes.ASTM A500-10. ASTM. 2010c. Standard Specification for Pipe, Steel,, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless.ASTM A53/A53M-10. ASTM. 2010d. Standard Specification for Welded and Seamless Steel Pipe Piles. ASTM 252-10. ASCE (American Society of Civil Engineers). 2010 Minimum Design Loads for Buildings and Other Structures.ASCE Standard ASCE 7-10. AWPA(American Wood Protection Association). 2006. Standard for the Care of Preservative-Treated Wood Products, AWPA M4-06. Bowles,J.E. 1996. Foundation Analysis and Design, 5th Ed. New York: McGraw-Hill. Collin,J.G. 2002. Timber Pile Design and Construction Manual. The Timber Piling Council of the American Wood Preservers Institute. FEMA (Federal Emergency Management Agency).'2006. Recommended Residential Construction for the Gulf Coast. FEMA P-550. FEMA. 2008a. Flood Damage-Resistant Materials Requirements. Technical Bulletin 2. 10-46 COASTAL CONSTRUCTION, MANUAL Volume II DESIGNING THE FOUNDATION 10 FEMA. 2008b. Free-of-Obstruction Requirements. Technical Bulletin 5. FEMA. 2008c. Openings in Foundation Walls and Walls of Enclosures. Technical Bulletin 1. FEMA. 2009a. Erosion, Scour, and Foundation Design.Available at http://www.fema.gov/library/ viewRecord.do?id=3539. Accessed on June 12, 2011. FEMA. 2009b. Recommended Residential Construction for Coastal Areas:Building on Strong and Safe Foundations. FEMA P-550, Second Edition. FEMA. 2010. Home Builder's Guide to Coastal Construction Technical Fact Sheet Series, FEMA P-499. ICC (International Code Council). 2008. Standard for Residential Construction in High-Wind Regions, ICC 600-2008. ICC: Country Club Hills, IL. ICC. 2011a. International Building Code. 2012 IBC. ICC: Country Club Hills, IL. ICC. 2011b. International Residential Code for One and Two Family Residences. 2012 IRC. ICC: Country Club Hills, IL. TMS (The Masonry Society). 2007.Masonry Designers'Guide, Fifth Edition, MDG-5. USDN (U.S. Department of the Navy). 1982. Foundation and Earth Structures, Design Manual 7.2. COASTAL CONSTRUCTION MANUAL 1 10-47