15LS03 Designing Wood-Frame Structures For High Winds V2
Transcript of 15LS03 Designing Wood-Frame Structures For High Winds V2
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CourseDescription
Woodframingisconducivetomeetingthechallengesofwind-resistivedesign.Amongitscharacteristics,woodcancarrysubstantiallygreatermaximumloadsforshortdurationsoftimeasisthecaseinhigh-windevents.Woodbuildingsalsotendtoincludemultipleandoftenredundantloadpathsforresistancetowindforces.Thispresentationwillcoverthedesignofabuilding’swind-resistingsystem,includingwindloadcalculations,diaphragms,shearwallsandcollectors.Loadpathcontinuitywillbediscussed,aswilluniquedesignconsiderationsfordesigningwood-framestructurestoresistuplift,in-plane,andout-of-planewindloads.Designexampleswillbepresentedtoillustraterelevantdesignproceduresanddetailingbestpractices.
LearningObjectives
1. ReviewtheparametersforbuildingwindloadcalculationsperASCE7andtheInternationalBuildingCode.
2. Examinethethreemaintypesofbuildingwindloads(uplift,in-plane,andout-of-plane)anddesignconsiderationsassociatedwitheach.
3. Discusscommonwood-frameshearwall,diaphragm,andtie-downsystems.
4. Recognizethebenefitsofredundancyinwind-resistingwood-framesystems.
MakingourBuildingsSafe- WindHighwindloadsactingonabuildingarearesultofavarietyoftypesofwindstormswhichhavedifferingnaturesandoccurrences.Buildingdesignshouldincludewindloadresistanceandaccountforthecharacteristicsofthetypeofstormsthatcanimpactthebuilding.
“Experiencehasshownthatcode-compliantwoodbuildingsperformexceedinglywellduringhighwindeventssuchashurricanes.Woodisstrongandmostwood-framebuildingsoffertheadvantageofrepetitivemembersandmultipleconnections,whichtogethercreateredundantloadpathstoeffectivelytransferwindforcesfromthebuildingenvelopetothefoundationandsoilbelow”.
UsingWoodtoResistWind:Benefits
QuoteSource:Wind-ResistiveDesignofWoodBuildings,AWC
Photo:NewGenesisApartments,Killefer Flammang Architects,KCKim,GBConstruction
WhyWood?
UsingWoodHelpsReduceYourEnvironmentalImpact
WoodProductsPlayaSignificantRoleinModernEconomy
WoodCostsLess
WoodisVersatile
WoodMeetsCode
WoodisDurable
WoodisRenewable
WindLoadsWindloadsactingonbuildingsaremodeledasuniformsurfaceloads.Windloadscancreatebothpositiveandnegativeloads(inwardsandoutwardsloads)onbuildingsurfacesandcreatethreedifferentloadingconditions:
• Uplift
• Racking/overturning
• Sliding/shear
WindLoadDemand
IBC:BaseCode– ReferencesASCE7fordeterminationofwindforcesonstructures
ASCE7:ReferencedStandard.Providesinformationrequiredtodeterminewindforcesona
structure
CalculatingWindLoads
• ASCE7-05§ Chpt.6:ContainedAllProvisions
• ASCE7-10§ Chpt.26:GeneralRequirements§ Chpt.27:MWFRS– Directional§ Chpt.28:MWFRS– Enveloped§ Chpt.29:OtherStructures§ Chpt.30:Components&Cladding§ Appendices
DetermineBasicWindSpeed,V
• ASCE7-05§ ASDLoads§ 90mphperfig.6-1
• ASCE7-10 (figuresincorporateimportancefactor)§ UltimateLoads§ 115mphperfigure26.5-1AforRKII
§ 120mphperfigure26.5-1BforRKIII&IV
§ 105mphperfigure26.5-1CforRKI
Note:RK=RiskCategoryImageSource:SKGhosh Associates
RunningtheNumbers:VelocityPressure
• qz =0.00256KzKztKdV2
§ qz =velocitypressure(psf)§ Kz – Exposurecoefficient,Table30.3-1(7-05Table6-3)
§ Kzt – Topographicfactor,Figure26.8-1(7-05Figure6-4)
§ Kd – Directionalityfactor,Table26.6-1(7-05Table6-4)
WindLoadsTypes
2TypesofWindLoads
• MWFRS– MainWindForceResistingSystemAnassemblageofstructuralelementsassignedtoprovidesupportandstabilityfortheoverallstructure.Thesystemgenerallyreceiveswindloadingfrommorethanonesurface.Eg.Shearwalls,diaphragms
• C&C– Components&CladdingElementsofthebuildingenvelopethatdonotqualifyaspartoftheMWFRS.Eg.Wallstuds
MWFRSMethodOptions
TwoMethodsofCalculatingMWFRSloads:• Envelope:Pressurecoefficientsrepresent“pseudo”loadingthatenvelopethedesired
moment,shear...Limitedtolow-rise
• Directional:Pressurecoefficientsreflectwindloadingoneachsurfaceasafunctionofwind
direction
MWFRSMethodOptions
Howtodecidewhichmethodtouse:Envelope:ASCE7-10Chapter28• Part1:Canbeusedforallregular-shapedenclosed&partiallyenclosedbuildingswithmeanroofheight≤60ft
• Part2(Simplified):Canbeusedforallregular-shaped,enclosed,simplediaphragmbuildingswithmeanroofheight≤60ft
MWFRSMethodOptions
Howtodecidewhichmethodtouse:Directional:ASCE7-10Chapter27• Part1:Canbeusedforallregular-shapedbuildings
• Part2(Simplified):Canbeusedforallregular-shaped,enclosed,simplediaphragmbuildingswithmeanroofheight≤160ft
MWFRSMethodOptions
ASCE7-10MWFRSOptions
Part1:Enclosed,PartiallyEnclosed,Open
BuildingsAllHeights
DirectionalMethod,CH27 EnvelopeMethodCH28
Part2:Enclosed,Simple
DiaphragmBuildingswithh≤160ft
Part1:Enclosed&PartiallyEnclosed Buildingswithh≤60ft
Part2:Enclosed,Simple
DiaphragmBuildingswithh≤60ft
Note:WindTunnelProcedure(ASCE7-10Chpt31)canalsobeused
Simplified,Directio
nal
Simplified,Envelope
SimpleDiaphragmBuildings
Abuildinginwhichbothwindwardandleewardwindloadsaretransmittedbyroofandverticallyspanningwallassemblies,throughcontinuousfloorandroofdiaphragms,totheMWFRS.
SimpleDiaphragmBuilding Non-SimpleDiaphragmBuilding
Example:FlatRoof,30’x60’Building:
Ch.27Directional
• WindwardWall(0.8)• LeewardWalls(-0.3)
• DetermineGustEffect(G)=0.85
• ForMWFRSGCpf =(1.1)(0.85)=0.935
Ch.28Enveloped
§ LimitedtoLow-Rise(h≤60’)§ WindwardWall(0.4)
§ LeewardWall(-0.29)
§ ForMWFRSGCpf =0.69
35%differenceinloadingnotaccountingforendzones.
ComparisonofmethodstocalculateMWFRS(GCpf)
ASCE7-10Figure28.4-1
ASCE7-10Figure27.4-1
MinimumWindLoads
ForboththeDirectional&EnvelopeMethods,considerminimumwindloads:ASCE7-10Sections27.1.5&28.4.4:
WindLoadsforMWFRSinanenclosedorpartiallyenclosedbuildingshallnotbelessthan:§ 16psf (ultimateor~10psf ASD)forwalls§ 8psf (ultimateor~5psf ASD)forroofs
Wallandroofloadsshallbeappliedsimultaneously.Thedesignwindforceforopenbuildingsshallbenotlessthan16psf ultimate(openbuildingprovisionsapplyonlytoDirectionalMethod).
BuildingEnclosure
Accountsfordegreetowhichwindforcescanenterandexitastructure,creatingvaryingamountsofinternalwindpressure
3buildingenclosureclassifications:Open,PartiallyEnclosed,andEnclosed
RunningtheNumbers:DesignWindPressure
• p=qh[(GCp)– (GCpi)]§ p=Designwindpressure(psf)§ qh =velocitypressure(psf)§ GCp:Externalpressurecoefficient
Figures27.4-1,28.4-1,30.4-1Note:Figure27.4-1alsorequiresGusteffectfactor(G)persection26.9
§ GCpi:Internalpressurecoefficient,Table26.11-1(7-05Figure6-5)
ActualWindLoads
ComparingASCE7-05toASCE7-10:LoadCombinations:
7.0.6D+W(ASCE7-05)7.0.6D+0.6W(ASCE7-10)
3SecondWindSpeed:90mph (ASCE7-05)115mph*√0.6=89mph(ASCE7-10)
Finalloadonbuildingisverysimilar
IBC’sAlternateAll-HeightsMethodIBCSection1609.6providesanalternativetotheDirectionalWindLoadProcedureinASCE7
AlternateAll-HeightsMethod
Limitationssuchas:• BuildingHeight≤75ft• BuildingHeight/Width≤4• Buildinghassimplediaphragm• Others(IBC1609.6.1)
Pnet =0.00256V2KzCnetKzt
IBC’sAlternateAll-HeightsMethod
Pnet =0.00256V2KzCnetKzt
• V=Basicwindspeed(ASCE7)
• Kz =Exposurecoefficient(ASCE7)
• Kzt =Topographicfactor(ASCE7)
• Cnet =Net-pressurecoefficient(IBCTable1609.6.2)
WindBorneDebrisRegions
PerASCE7-10,section26.2,WindBorneDebrisregionsareAreaswithinhurricane-proneregionswhereimpactprotectionisrequiredforglazedopenings(buildingsinRiskCategoryIareexempt– ASCE26.10.3&IBC1609.1.2)
Protectionofglazedopeningsisrequired(ASCE726.10.3):
• Within1mileofthecoastalmeanhighwaterlinewherethebasicwindspeedisequaltoorgreaterthan130mph,or
• Inareaswherethebasicwindspeedisequaltoorgreaterthan140mph
• Otherexemptions,testingrequirementsgiveninASCE7-10,section26.10.3
WindBorneDebrisRegions
Failedopeningscanchangeastructurefromenclosedtopartiallyenclosed,significantlyincreasingwindforces
UpliftWindLoads
Uplift– Outward(suction)forceactingonroof
Loadpath- rooftofoundationrequiredunlessdeadloadisgreaterthanuplift
MethodstoResistUpliftLoads
• Mechanicalconnectors(straps,hurricaneties,screws,threadedrods)
• Sheathing
• DeadLoads
Source:strongtie.com
UpliftResistance:WallSheathing
• Whenjoints,fastenersareconsidered,canusesheathingtoresistuplift
• SDPWSSection4.4
SDPWSFigure4I
Uplift:MWFRSorC&C?
ConsidermemberpartofMWFRSif:• TributaryArea>700ft2 perASCE7-1030.2.3• LoadcomingfrommorethanonesurfaceperASCE7-1026.2
Uplift:MWFRSorC&C?
AWC’sWFCMcommentaryC1.1.2statesthatMWFRSisusedforallupliftconditions:
TherationaleforusingMWFRSloadsforcomputingtheupliftofroofassembliesrecognizesthatthespatialandtemporalpressurefluctuationsthatcausethehighercoefficientsforcomponentsandcladdingareeffectivelyaveragedbywindeffectsondifferentroofsurfaces.
Uplift:MWFRSorC&C?
ASCE7-1026.2commentaryprovidessomediscussiononuplift&MWFRSvs.C&C.
ComponentsreceivewindloadsdirectlyorfromcladdingandtransfertheloadtotheMWFRS.Examplesofcomponentsincludefasteners,purlins,girts,studs,roofdecking,androoftrusses.ComponentscanbepartoftheMWFRSwhentheyactasshearwallsorroofdiaphragms,buttheymayalsobeloadedasindividualcomponents.
EffectiveWindArea
Forwinddesign,tributaryareadoesnotnecessarily=effectivewindarea
EffectiveWindArea(EWA)- Twocases:• Areaofbuildingsurfacecontributingtoforcebeing
considered(tributaryarea)• Longandnarrowarea(wallstuds,rooftrusses):width
ofeffectiveareamaybetakenas1/3length;increaseseffectivearea,decreasesload(perASCE7-10section26.2commentary);EWA=L2/3
EffectiveWindAreaExample
44’-0”
Trusses@2’o.c.
44’-0”
Trusses@2’o.c.
Trib.A=(44)(2)=88ft2 EWA=442/3=645ft2
UpliftExampleCalculation
• RoofFramingRafter• 20’Span• 2’Spacing• 2’Overhang• 115mphExposureB• RoofH=80ft• 65’x220’
Photocredit:MattTodd&PBArchitects
MWFRS- ExternalPressureCoefficient
Lookatwindactingonbuilding’slongside:L=65ft,h/L=80/65=1.23Cp =1.3,-0.18
ASCE7-10Fig.27.4-1
• GCp:(0.85)(-1.3)=1.105(26.9.4&Fig.27.4-1)• GCpi:±0.18(Table26.11-1)• qh =0.00256KzKztKdV2
§ Kz :0.93– Table27.3-1§ Kzt :1.00- Figure26.8-1§ Kd :0.85- Table26.6-1§ Vu:115mph
• qh =26.8psf• p=(26.8psf)(-1.105+(-0.18))=34.4psf
MWFRS- Runningthenumbers
MWFRS- RoofOverhangpersection27.4.4• ForOverhangs:ASCE727.4.4– useCp =0.8onundersideofoverhang,usesametoppressurescalculatedfortyp.roof
• poh =(26.8psf)(-0.8)(0.85)=18.2psf• pext =(26.8psf)(-1.105)=29.6psf• poh net=18.2+29.6=47.8psf
Poh
pext
PerASCE7-10section27.4.4
pint
MWRFS- DeterminingtheUpliftLoad• p=(34.4psf)(2ft)=68.8plf• poh =(47.8psf)(2ft)=95.6plf
68.8plf
Uplift=0.6(95.6plf(2ft.)+68.8plf*20ft/2)=528lbsDeadLoad=0.6((2+20/2)*10psf*2ft)=144lbsNetUpliftatLeftSupport=528lbs -144lbs =384lbsNote: Itiscommonpracticetouse2sets ofdead loads:highestpotential dead loadsforgravity,lowestpotential deadloadsforuplift
95.6plf
C&C- ExternalPressureCoefficient3zoneswithdifferingwindloads:
1:Field2:Perimeter3:Salientcorners
a=smallerof10%ofleasthorizontaldimensionor0.4h,butnotlessthaneither4%ofleasthorizontaldimensionof3ft
ASCE7-10Fig.30.4-2A
C&C- ExternalPressureCoefficient– Fig.30.4-2A
EWA=H2/3=222/3=161ft2
GCP =-1.1FORINTERIOR
ASCE7-10Fig.30.4-2A
• GCp:-1.1(Figure30.4-2A)• GCpi:±0.18(Table26.11-1)• qh =0.00256KzKztKdV2
§ Kz :0.93- Table30.3-1§ Kzt :1.00- Figure26.8-1§ Kd :0.85- Table26.6-1§ Vu:115mph
• qh =26.8psf• p=(26.8psf)(-1.1+(-0.18))=34.3psf
C&C- Runningthenumbers– Zone2
C&C- RoofOverhangpersection30.10• ForOverhangsFigures30.4-2A&30.10-1areutilized• poh =26.8psf(1.7+0.18)=50.4psf• ps =pw =34.3psf• poh net=50.4+34.3=84.7psf
ps
pW
pOH
EWA=2*2=4sf
GCp =-1.7
PerASCE7-10Fig.30.10-1ASCE7-10Fig.30.4-2A
C&C- DeterminingtheUpliftLoad• p=(34.3psf)(2ft)=68.6plf• poh =(84.7psf)(2ft)=169.4plf
68.6plf
Uplift=0.6(169.4plf(2ft.)+68.6plf*20ft/2)=615lbsDeadLoad=0.6((2+20/2)*10psf*2ft)=144lbsNetUpliftatLeftSupport=615lbs -144lbs =471lbsNote: Itiscommonpracticetouse2sets ofdead loads:highestpotential dead loadsforgravity,lowestpotential deadloadsforuplift
169.4plf
WindLoadsUniformsurfacewindloadsgenerallyincreasewithbuildingheight
ASCE7-10Fig.27-6.1
Ifwindloadsvarywithbuildingheight,commontousehigherwindloadoverasinglestoryorbuilding
Panels
Hinges
L/dRatio
Unbraced Length
WallVeneer
WindonlyloadingC&C
DesignProperties
WallDesignConsiderations
LoadsintoWSPWindloadsaretransferredtowallframingstudsthroughwoodstructuralpanels(sheathing)
SDPWSTable3.2.1
ForASDCapacity:DivideNominalCapacityby1.6
ForLRFDCapacity:MultiplyNominalCapacityby0.85
FullHeightStudsatGableEndWalls
• Ifnoopeningsingableendwallexist,candesignstudstospanfromfloor/foundationtoroof(varyingstudheights).Mayrequirecloserstudspacings attallerportionsofwall
GableEndWallGirts&Jambs
• Oftengableendwallsarelocations oflargewindows
• Horizontallyspanningmember inplaneofwallbreaksstud length,providesallowableopening
Verticallyspanningjambs
Horizontallyspanning
girts
Gypsum&WeakAxisBuckling
NDSCommentary:“Experiencehasshownthatanycodeallowedthicknessofgypsumboard,hardwoodplywood,orotherinteriorfinishadequatelyfasteneddirectlytostudswillprovideadequatelateralsupportofthestudacrossitsthicknessirrespectiveofthetypeorthicknessofexteriorsheathingand/orfinishused.”
CalculatingDeflection– IBCTable1604.3
ForΔ ofmostbrittlefinishesusel/240
ForC&Cpressuresa30%loadreductionisallowedforΔ only(IBCTable1604.3footnotef)
f.Thewindload ispermitted tobetakenas0.42times the"component andcladding” loadsforthepurposeofdetermining deflection limits herein.
WoodStudswithBrickVeneer- Deflection
IBCTable1604.3:min.walldeflectionwithbrittlefinishes=L/240
BrickIndustryAssociationrecommendsmuchstricterlimits
StructureMagazineMay2008article,HaroldSprague
BIATechNote28
Example:LargeDiamondRetailer22’tallwoodframedwalls.
Assumestuds16”o.c.
130mphExposureB
LeastHorizontalDim.=64ft.
ExternalPressureCoefficients– WallZones4&5
a=Lesserof:
• 10%leasthorizontaldimension(LHD)64’*0.1=6.4’
• 0.4h=0.4*22=8.8’.Butnotlessthan:
• 0.04LHD=2.6’or3’
Usea=6.4’forzone5
ExternalPressureCoefficients- Walls
Assumewallstudsare22’long
EWA=h2/3=161ft2
Zone4:
GCpf =-0.89
GCpi =-0.18(Table26.11-1)
Zone5:
GCpf=-1.0
ASCE7-10Figure30.4-1
Runningthenumbers– Zone4
• GCpf:0.89(Figure30.4-1)• GCpi:0.18(Table26.11-1)• qh =0.00256KzKztKdV2
§ Kh :0.70- Table30.3-1§ Kzt :1.00- Figure26.8-1§ Kd :0.85- Table26.6-1§ V:130mph
• qh =25.74psf• p=25.74psf(0.89+0.18)=27.54psf• 0.6W=0.6(27.54)=16.52psf
LumberDesignProperties
DesignPropertiesfromNDSSupplement.
Assume2x8DouglasFir-Larch#2Studs,16”o.c.
RepetitiveMemberadjustment=1.25
SizeFactor=1.2
DurationofLoad=1.6
StudRepetitiveMemberFactorNoteonstudrepetitivememberfactor:
NDSsection4.3.9:CR =1.15
SDPWSTable3.1.1.1largerCR factorsforstudsinbending,16”spacingmaxincreasedto24”in2015SDPWS),interiorcoveredwithmin.½”gypsum,exteriorcoveredwithmin.3/8”WSP,otherfastenerrequirements
DESIGNPROPERTIES
Fb (psi) 900 NDSSupp.Table 4A
CD 1.6 NDSTable2.3.2
CR 1.25 SDPWS Table 3.1.1
CF 1.2 NDSSupp.Table 4A
E(psi) 1600000 NDSSupp.Table 4A
Sx (in3) 13.1 CalculatedNDS3.3-4
I(in4) 47.6 CalculatedNDS3.3-3
Soisourstudgoingtowork?
Twoofthemostcriticaldesignparametersarebendinganddeflection.
Studswork!
IBCTable1604.3footnotef
• GCp:1.00(Figure30.4-1)• GCpi:0.18(Table26.11-1)• qh =0.00256KzKztKdV2
§ Kh :0.70- Table30.3-1§ Kzt :1.00- Figure26.8-1§ Kd :0.85- Table26.6-1§ V:130mph
• qh =25.74psf• p=25.74psf(1.0+0.18)=30.37psf• 0.6W=0.6(30.37)=18.22psf
Runningthenumbers– Zone5
12”StudSpacing
Sincestuddepthcannotbeincreasedconsiderreducingstudspacingto12”inallZone5areas:
Studswork!– Use2x8@16”o.c.typical,use2x8@12”o.c.incorners(Zone5areas)
IBCTable1604.3footnotef
WallDesignConsiderations
Fortallwallswhileitislesslikelyforcombinedbendingandaxialtocontrol
• MainWindForceLoadsmaybe
utilized
• Loadcombinations(ASCE7Chpt 2)
for:
§ wind+deador
§ dead+0.75live+0.75rooflive
(orsnow)
D,L,S
W
WallDesignConsiderations
Forotherdesignissuesseethearticle:
• ConsiderationsinWindDesignofWoodStructures
• FreedownloadfromAWCavailableat:http://www.awc.org/pdf/codes-standards/publications/archives/AWC-
Considerations-0310.pdf
WallStudDesignAidWesternWoodProductsAssociation(WWPA)DesignSuite:
http://www.wwpa.org/TECHGUIDE/DesignSoftware/tabid/859/Default.aspx
StudtoDiaphragm
WINDLOAD
DIAPHRAGMSHEATHING
Floor/Roofframingparalleltowalls(addblocking)
FLOORJOIST
BLOCKING
VisualCue
VisualCue:FloorBeaminPlan=DiaphragminElevation
FloorBeam
FloorBeam
FloorBeam
FloorJoists
FloorFramingPlan
FloorJoists
VisualCue
VisualCue:FloorBeaminPlan=DiaphragminElevation
Diaphragm
Diaphragm
Foundation
WallStuds
WallFramingElevation
WallStuds
Floor- BendingMember
• SimplySupportedMember:loadingcausescompressioninoneedgeofmember,tensioninotheredge
Compressionedge
Tensionedge
Loadingdirection
ReactionReaction
WindLoadPath- Lateral
•Diaphragmactslikeadeepbeam.• Sheathingcarriesshearforces• ChordshaveT&Cforces• Rimboardtransfersshear
DIAPHRAGM
AssumeBasicWindSpeed=115mphUltimate
ExposureB
DiaphragmDesign
• Capacity
Shearwall Design
• Conventional
• ForceTransferAroundOpening
• PerforatedShearwall
Example:RetailRestaurant
RetailRestaurant– DiaphragmDesign
84’
34’
10’6’ 8’5’
6’
6’
6’
6’
6’
3’3’
4’
29’24’
CriticalShearwall atfrontofbuilding
CheckDiaphragmforwindloadson84’wall
RetailRestaurant– DiaphragmDesign
CriticalShearwall atfrontofbuilding
CheckDiaphragmforwindloadson84’wall
84’
34’
10’6’ 8’5’
6’
6’
6’
6’
6’
3’3’
4’
29’24’
DiaphragmAspectRatios
SDPWSTABLE4.2.4
TYPE- MAXIMUMLENGTH/WIDTHRATIO
Foran84x34diaphragmtheaspectratiois2.5<3.
DiaphragmaspectratioisOK.
Woodstructural panel,unblocked 3:1
Woodstructural panel,blocked 4:1
Single-layerstraightlumbersheathing 2:1
Single-layerdiagonallumbersheathing 3:1
Double-layerdiagonallumbersheathing 4:1
CalculatingMWFRSWindLoadsCalculatewindpressureusingDirectionalMethod(ASCE7Chpt 27)
p=qh[(GCpf)-(GCpi)]
qh =0.00256*0.57*1.0*0.85*1152*1=16.4psf
GCpf =0.85*[0.8– (-0.3)]=0.935
GCpi =0.18- 0.18=0
p=(16.4psf)(0.935)=15.34psf
0.6*W=0.6*15.34=9.2 psf onwalls
Usemin9.6psf perASCE27.1.5
ASCE7-10Figure27.4-1
ParapetDesign– Figure27.6-2
Atparapetswindwardandleewardpressuresoccuroneachparapet.
Section27.4.5:Pp =q(GCpn)GCpn =1.5Windwardparapet,-1.0LeewardparapetWindwardParapetGCpf is1.5:16.4*1.5*0.6=14.76psfLeewardParapetGCpf is1.0:16.4*1.0*0.6=9.84psfNetParapet=14.76+9.84=24.6psf
RetailRestaurant– DiaphragmDesign
84’
34’
10’6’ 8’5’
6’
6’
6’
6’
6’4’
29’24’
10’
3’
3’
P=(9.6psf*(5’+3’)+(24.6)*3’)*(84’/2)=6,325lb
νdiaphragm=6,325lb/34’νdiaphragm=186plf
P
DiaphragmTypes
CASE1DIAPHRAGM•HigherShearValues•Panelsperpendiculartofloorframingforimprovedperformance
CASES2-6Maybepreferredforlowsheardemandwherechangingframingdirectionhelps•HVACruns•FireBlocking/DraftStopping
RoofTrusses4x8sheathingN-S
DiaphragmCapacity- SDPWSChpt 4
• CapacitiesareNominal:ModifybyASDreductionfactorof2,ModifybyLRFDmultiplicationfactorof0.8
• CapacityisreducedforspecieswithSpecificGravity<0.5• ForSprucePineFirmultiplyby0.92
DiaphragmCapacity:SDPWSTable4.2C
PANELGRADE
COMMONNAILSIZEORSTAPLEf
LENGTHANDGAGE
MINIMUMFASTENERPENETRATIONINFRAMING
MINIMUMPANELTHIICKNESS
MINIMUMNOMINALWIDTHOFFRAMINGMEMBERSATADJOININGPANELEDGESANDBOUNDARIESg
NAILSPACINGATALLPANELEDGES
Case1(Nounblockededgesorcontinuousjointsparalleltoload)
Allotherconfigurations(Cases2,3,4,5and6)
Sheathing&singlefloor
8d(2½“x0.131”)
13/8”
7/16”
2IN. 6IN. 460(Seismic)645(Wind)
340(Seismic)475(Wind)
3IN. 6IN. 510(Seismic)715(Wind)
380(Seismic)530(Wind)
CapacityisreducedforspecieswithSpecificGravity<0.5.ForSprucePineFirmultiplyby0.92
Capacity =(645plf)(0.92)/2=297plf297plf >186plf,diaphragmisadequatewithsheathing&fasteningasshownabove
TransferringDiaphragmShearForces
BLOCKTOTRANSFERFORCES
PARAPET
NOTE:PARAPETKICKERSMAYBEREQUIREDFORTALLTRUSSPARAPETS
TransferringDiaphragmShearForces
SHEARWALLBELOW
SHEARFORCEFROMDIAPHRAGM
RIMJOISTPROVIDESDIAPHRAGMLOAD
TRANSFER
DiaphragmtoShearwall Fastener
RIMBOARD
FLOORJOIST
TOPPLATE
TOENAIL150plf (ASD)LIMITINSDCD,E,F(SDPWS4.1.7)
METALCLIPSFORADD’LSTRENGTH
RoofDiaphragmtoShearwall
BLOCKINGTRANSFERSSHEARFORCESFROMROOFDIAPHRAGMTO
TRUSS
DIAPHRAGM
SHEARWALL
TRUSSTOWALLCONNECTION
COMPLETESLOADPATH
• Diaphragmscanbeidealizedasflexible,semi-rigid,orrigid
• ASCE7-10Section26.2statesthatdiaphragmsconstructedofwoodstructuralpanelsarepermittedtobeidealizedasflexible
WoodEducationInstitute
DiaphragmFlexibility
DiaphragmFlexibilitySomebuildinglayoutsmayrequirediaphragmdesigntoaccountforcantilevers,oropenfrontstructures.• Trendsinmid-rise,multi-familybuildingstowardfewer
exteriorshearwallsmoveintosemi-rigid&rigidmodeling
Cant.
SWSWSWSW
SWSWSWSWSW
SW
NoexteriorShearwalls
Cor
ridor
onl
y sh
ear w
alls
Offs
et s
hear
wal
ls
OpenFrontStructures(SDPWS4.2.5)
• Canidealizediaphragmasrigidifmax.in-planediaphragm
deflectionis≤2xavg.storydriftofverticalelements
• Ifnotidealizingasflexibleorrigid,mayusesemi-rigidanalysis,
distributesshearbasedonrelativestiffnessofbothdiaphragm
andverticalresistingelements
• Commontouseenvelopeanalysisinlieuofsemi-rigidanalysis• 2015SDPWS:DiaphragmCantilever≤35feet
AdditionalConsiderations:
• L/WRatio
• Irregularities&TorsionalEffects
• Diaphragmdeflections,especiallyatcorners
Shearwall &DiaphragmDeflection
Whencalculatingshearwall anddiaphragmdeflections,valuesofapparentshearstiffness,Ga,arerequired,butarenotprovidedforwinddesigninSDPWS
Shearwall &DiaphragmDeflectionAWCFAQ:Cantheeffectiveshearstiffnessvalues,Ga,inSDPWSbeusedforcalculationofdiaphragmandshearwalldeflectionsduetowindloads?
Valuesofapparentshearstiffness,Ga,aretabulatedinseismiccolumnsofthe SDPWS tofacilitatecalculationofseismicstorydriftinaccordancewithASCE7MinimumDesignLoadsforBuildingsandOtherStructures.ValuesofGa areequallyapplicableforcalculation ofthesheardeformationcomponentoftotaldeflectionduetowindloadsuptotheASDwindunitshearvaluecalculatedasvw/2.0.Thislevelofunitshearforwindisidenticalto1.4timestheASDseismicunitshearcapacityforwhichapparentshearstiffnessvalueswereoriginallydeveloped.
http://awc.org/faqs/general/can-the-effective-shear-stiffness-values-ga-in-special-design-provisions-for-wind-and-seismic-%28sdpws%29-be-used-for-calculation-of-diaphragm-and-shear-wall-deflections-due-to-wind-loads
WSPShearwall Capacity• CapacitieslistedinAWC’sSpecialDesign
ProvisionsforWindandSeismic(SDPWS)• Sheathedshearwallsmostcommon.Canalso
usehorizontalanddiagonalboardsheathing,gypsumpanels,fiberboard,lathandplaster,andothers
• Blockedshearwallsmostcommon.SDPWShasreductionfactorsforunblockedshearwalls
• Notethatcapacitiesaregivenasnominal:mustbeadjustedbyareductionorresistancefactortodetermineallowableunitshearcapacity(ASD)orfactoredunitshearresistance(LRFD)
WindLoadscreateshear(sliding)andrackingforcesonastructure
Slidingresistedbyshearwall baseanchorageRackingresistedbyshearpanel&fasteners
Shearwall Functions
ShearWallComponents:WallFraming
Strut/collector
WallFraming(Studs)
BlockingBetweenStudsatAllPanelEdges
WallTopPlates
WallSolePlate
Note:Canuse“un-blocked”wallbutcapacitiescanbesignificantlylower:SDPWS4.3.3
ShearWallComponents:WSP&Fasteners
Strut/collector
FieldorIntermediateNailing– Typ.12”o.c.
BoundaryNailing–Typ.2”– 6”o.c.
BoundaryNailing:Attachesall4edgesofeverypaneltowallframing(studs,blocking,top&soleplates)
FieldorIntermediateNailing:Attachespaneltointermediatewallframing(studs)notalongpaneledges
SheathingPanelsOSBorPlywood
Duetocantilevernatureofshearwalls,overturningforcesarealsogenerated
Overturningforcesareresistedbytension/compressioncouple–tensionportionresistedbydeadloadsandholddownanchors
Shearwalls - Overturning
ShearWallComponents:BaseAnchorage,EndPosts&HoldDowns
Strut/collector
SolePlateUniformAnchorage:Transfersshearfromwallsoleplatetofloor/wallorfoundationbelow.
SolePlateUniformAnchorage(Nails,Screws,Anchor
Bolts)
WallEndPost&HoldDown:Transfersverticaltension&compressionforcestofloor/wallorfoundationbelow.
WallEndPost&HoldDown
WallEndPosts(SizedforTension&Compression)
Shearwall HoldDowns
ContinuousRodTieDownswithShrinkageCompensation
Devices Source:hardyframe.com
Source:cteg.com
Shearwall Placement- Symmetrical
INTHISCASEDRAGSTRUTSCARRYLITTLE LOAD
TOPPLATE– NTSDRAGSTRUT
SHEARWALLS
WINDWARD
LEEWARD
Shearwall Placement– LargeDragStruts
INTHISCASEDRAGSTRUTSTRANSFERLEEWARDLOAD
TOPPLATE– NTSDRAGSTRUTSHEARWALLS
WINDWARD
LEEWARD
DragStruts&IsolatedWalls
INSOMECASESDOUBLETOPPLATEISINADEQUATE
WHATTOWATCHFOR:
• ISOLATEDSWWITHHEAVYNAILING• NOSHEARWALLSWITHIN10’OFWALLCORNER
Shearwalls inaLine- Stiffness• Windloadstomultipleshearwalls inthesamelinearedistributed
basedonshearwall stiffness• Ifwallshavethesameframing&sheathing,assumedtohavethe
sameper-footstiffness&loadsaredistributedbasedonwalllength• Eg.5’longwallreceives5/(5+12)=29%oftotalload
12’longwallreceives12/(5+12)=71%oftotalload
SHEARWALLLENGTHSDETERMINESTIFFNESS&LOADSHARING5’12’
Shearwall AspectRatio
NDSSDPWSTABLE4.3.4
MAXIMUMSHEARWALLDIMENSIONRATIOS
SeeSDPWSTable4.3.4forfootnotes
Woodstructural panels,blocked Forotherthanseismic:3½:11
Forseismic: 2:11
Woodstructural panels,unblocked 2:1
Diagonalsheathing, single 2:1
StructuralFiberboard 3½:13
Gypsumboard,portland cement plaster 2:12
L
H
AR=H/L
EngineeredShearWallSystemsw/WSP
SolidorSegmentedWalls
PerforatedWallsForceTransferAround
OpeningsWalls
RetailRestaurant– Shearwall Design
84’
34’
10’6’ 8’5’
6’
6’
6’
6’
6’4’
29’24’
10’
3’
3’
P =7,602lb – fromdiaphragmcalcs usingDirectionalMethod
Let’sseewhathappenswhenweuseEnvelopeMethodtocalculateMWFRSloadstofrontshearwall
P
CalculatingMWFRSWindLoadsCalculatewindpressureusingEnvelopeMethod(ASCE7Chpt28)
p=qh[(GCpf)-(GCpi)]
qh =0.00256*0.70*1.0*0.85*1152*1=20.14psf
GCpf (Zones1&4) =0.4– (-0.29)=0.69(ASCE7Fig.28.4-1)
GCpf (Zones1E&4E) =0.61– (-0.43)=1.04(ASCE7Fig.28.4-1)
GCpi =0.18- 0.18=0
P1&4=(20.14psf)(0.69)=13.9psf;0.6*W=0.6*13.9=8.3psfwallstyp.
P1E&4E=(20.14psf)(1.04)=20.9psf;0.6*W=0.6*20.9=12.5psf wallscrnr
ASCE7-10Figure28.4-1
CalculatingMWFRSWindLoads
ASCE7-10Figure28.4-1
a=Lesserof:
• 10%leasthorizontaldimension(LHD)34’*0.1=3.4’
• 0.4h=0.4*13’=5.2’.Butnotlessthan:
• 0.04LHD=1.4’or3’
Usea=3.4’forzones1E&4E
2a=3.4’*2=6.8’
ParapetDesign– Section28.4.2
Atparapetswindwardandleewardpressuresoccuroneachparapet.
Section28.4.2:Pp =q(GCpn)GCpn =1.5Windwardparapet,-1.0LeewardparapetWindwardParapetGCpf is1.5:20.14*1.5*0.6=18.12psfLeewardParapetGCpf is1.0:20.14*1.0*0.6=12.08psfNetParapet=18.12+12.08=30.2psf
RetailRestaurant– Shearwall Design
84’
34’
10’6’ 8’5’
6’
6’
6’
6’
6’4’
29’24’
10’
3’
3’
P
6.8’12.5psf8.3psf
77.2’
P=(8.3psf*(5’+3’)+(30.2)*3’)*(84’/2)+((12.5psf-8.3psf)*(5’+3’))*6.8’*(77.2’/84’)=6,804lb(forcomparison:Directionalmethodgaveus6,325lb)
Shearwall AspectRatios
10’
3’
3’34’
6’ 6’ 6’ 6’ 6’2’ 2’
10’
• CheckAspectRatios:AssumeblockedWSPShearwall• 10’/2’=5>3.5;Inadequate• 10’/6’=1.67<3.5;OK
FrontWallElevation
• CheckAspectRatios:AssumeblockedWSPShearwall• 10’/2’=5>3.5;Inadequate• 10’/6’=1.67<3.5;OK
Shearwall AspectRatios
10’
3’
3’34’
6’ 6’ 6’ 6’ 6’2’ 2’
10’
νshearwall =6,804lb/12’=567plf
ConventionalShearwall Capacities
νshearwall =567plf
Assume15/32”,StructuralIsheathingattachedwith8dnails
NominalTabulatedCapacity=1540plfAdjustedASDCapacity =(1370plf)(0.92)/2=630plf630plf >567plf,OK8dnailsat3”o.c.acceptable
PANELGRADE FASTENERTYPE&SIZE
MINIMUMPANELTHIICKNESS
MINIMUMFASTENERPENETRATIONINFRAMING
NAIL SPACINGATALLPANELEDGES
PANEL EDGEFASTENERSPACING
WoodStructuralPanels–Sheathing
8d(2½“x0.131”)
15/32” 13/8” 3IN. 980(Seismic)1370(Wind)
SDPWSTable4.3A
DesignTableDetails– 16”o.c.Studs
• Spacefasteners12inchesoncenteronintermediatesupports(SDPWS4.3.7.1.3)
• Ifnailspacingis2”o.c.use3inchnominalframing (SDPWS4.3.7.1.4)
• If10dnailsareutilizedalongwith3incho.c.edgenailingusenominal3xframing(SDPWS4.3.7.1.4)
• Ifnominalunitshearoneithersideofwallexceeds700plf inSDCD,E,orF,usenominal3xframing(SDPWS4.3.7.1.4)
ConventionalShearwall Overturning
νshearwall =567plfHolddownsrequiredatshearwallsT=νhT=567plf*10’=5,670lb
Holddowncapacity=7,045lbManyavailableprefabricatedholddownswithcapacitieslistedbymanufacturers
34’
6’ 6’ 6’ 6’ 6’2’ 2’
10’
ConventionalShearwall Overturningνshearwall =567plfPostsarealsorequiredatendsofthewalltoresistcompressionforcesC=T=νhC=567plf*10’=5,670lb
6’ 6’ 6’ 6’ 6’2’ 2’
10’
SizepostforbearingonwallsoleplateAssume2x6wall,Requiredpostwidth=5,670lb/(565psi)(5.5in)=1.8in;Use2-2x6postmin.
ConventionalShearwall BaseAnchorage• νshearwall =567plf• ½”AnchorBoltcapacityforwoodbearing=680lb*1.6=1,088lb
perNDSTable11E• Spacing=1088lb/567plf =1’-11”o.c.max.
PerforatedShearWallMethod
HOLDDOWNSATENDOFWALL
WSPSHEATHING
Fewerholddownsrequired,shearcapacityisreduced
Uniformupliftatbaseofwallrequired– magnitude=shearforce– SDPWS4.3.6.4.2.1
• CheckAspectRatios:AssumeblockedWSPShearwall• 10’/2’=5>3.5;Inadequate• 10’/6’=1.67<3.5;OKUseonlyfullheightsheathedsectionstoresistshear
PerforatedShearwall Design
10’
3’
3’34’
6’ 6’ 6’ 6’ 6’2’ 2’
10’
νshearwall =6,804lb/12’=567plf
TotalPerforatedShearwall
PerforatedShearwall CapacityWallhas12’/18’=67%fullheightsheathing,max.openingH=6’-8”
Multiplycapacityby0.75foropening2H/3
Reducedcapacityis630plf*0.75=473plf <567plf,Inadequate
SDPWSTable4.3.3.5
PerforatedShearwall Capacity
νshearwall =567plf
Tryreducingnailspacingto2”with8dnails– willrequire3xframing
NominalTabulatedCapacity=1790plfAdjustedASDCapacity=(1790plf)(0.92)(0.75)/2=618plf618plf >567plf,OK8dnailsat2”o.c.acceptableforperforatedwall
PANELGRADE FASTENERTYPE&SIZE
MINIMUMPANELTHIICKNESS
MINIMUMFASTENERPENETRATIONINFRAMING
NAIL SPACINGATALLPANELEDGES
PANEL EDGEFASTENERSPACING
WoodStructuralPanels–Sheathing
8d(2½“x0.131”)
15/32” 13/8” 2IN. 1280(Seismic)1790(Wind)
SDPWSTable4.3A
PerforatedShearwall Overturning
34’
6’ 6’ 6’ 6’ 6’2’ 2’
10’
νshearwall =567plfHolddownsrequiredatendsofperforatedwallT=νh/CoT=567plf*10’/0.75=7,560lb
Holddowncapacityfromsegmentedwalloption=7,045lb,Inadequate– needtoselecthighercapacityholddown
PerforatedShearwall Uplift
34’
6’ 6’ 6’ 6’ 6’2’ 2’
10’
νshearwall =567plf/0.75=756plf,usesamemagnitudeforuniformupliftatfullheightsegmentsOneoptionistouseanchorboltswithlargewasherstoresistupliftinbearingIfnetwasherarea=8in2,canresist(565psi)(8in2)=4,520lb inuplift• Max.anchorboltspacing=4,520lb/756plf =5’-11”o.c.• Willalsoneedtocheckshearloadsonanchorboltsforcontrolling
case
FTAOShearwallsMethodologies• Shearwall designmethodologywhichaccountsforsheathed
portionsofwallaboveandbelowopenings(perforatedneglects)• Openingsaccountedforbyreinforcingedgesusingstrappingor
framing• SDPWS4.3.5.2providesspecificrequirements
• H/Lratiodefinedbywallpier• Min.wallpierwidth=2’-0”
• Reducednumberofholddowns(onlyatendsoftotalwall)
• Thereare3mainmethodsofFTAOanalysis;SDPWSdoesnotrequireoneparticularmethodbeused,onlythatdesignis“basedonarationalanalysis”• DragStrut,CantileverBeam,&DiekmannDesignOptions
FTAOShearwallsDragStrutDesignMethodology• Forcesarecollectedandconcentratedintotheareasaboveand
belowtheopenings• Strapforcesareafunctionofopeningandpierwidths
APAFormM410
FTAOShearwallsCantileverBeamDesignMethodology• Forcesaretreatedasmomentcouples• Segmentedpanelsarepiersatsidesofopenings• Strapforcesareafunctionofwallheightaboveandbelow
openingsandpierwidths
APAFormM410
FTAOShearwallsDiekmann DesignMethodology• Assumeswallbehavesasmonlithic trussorframe• Internalforcesresolvedviaprinciplesofstatics• Wallsectionsonallsidesofopeningareassumedtohaveapoint
ofinflectionatmidlength,producingnoforceintheinnerchordsofthesections
APAFormM410
FTAOShearwall DesignAid
ImagesSource:RISATechnologies
RISATechnologiesdesignsoftwareincludesanoptiontodesignFTAOwoodsheathedshearwalllsusingfiniteelementanalysis(FEM)
Double-SidedShearwalls
High-strengthwoodshearwallscanbedouble-sidedwithWSPsheathingoneachside:SDPWS4.3.3.3SummingShearCapacities:Forshearwallssheathedwiththesameconstructionandmaterialsonoppositesidesofthesamewall,thecombinednominalunitshearcapacity shallbepermittedtobetakenastwicethenominalunitshearcapacityforanequivalentshearwallsheathedononeside(4.3.5.3hasmaxcapacitiesfordouble-sidedperforatedwalls)
Double-SidedShearwalls
Thereisalsoanoptiontohaveasinglesided,doublesheathedshearwall.
TestingandreportbyAPAconcludethatitispermissibletousethecapacityofthewallthesameasiftherewasonelayerofWSPoneachsideofthewallprovidedthatanumberofcriteriaaremetincluding:• Framingmembersatpanel
jointsare3xor2-2x• Minimumnailspacingis4”• Others
UsingPrefabShearwalls
Considerations:EngineeredNarrowWallSection
Proprietary
LargeHold-downforces
Deflections
PrefabWallAspectRatios
10’
3’
3’34’
30’2’ 2’
10’
• AspectRatioInadequate• 10’/2’=5>3.5• V=6,804lb• Let’stryaprefabshearwall
PrescriptivePortalFrameSystems
• SeniorLiving• Apartments/Condos• MixedUse• StudentHousing• AffordableHousing• Hotels
WhereWoodisaviableoption,it’slikelythemostappropriatechoice.
PrescriptiveCodePortalFramesIBC2308.9.3.2
ProprietaryPortalFrames
Source:strongtie.com
PrescriptivePortalFrameSystems
• SeniorLiving• Apartments/Condos• MixedUse• StudentHousing• AffordableHousing• Hotels
WhereWoodisaviableoption,it’slikelythemostappropriatechoice.
APAReportTT-100F
Allowable DesignShearValues
Min.Width(in.)
Max.Height(ft.)
Shear(lb)
168 850
10 625
248 1,675
10 1,125
GypsumShearwalls• LowercapacitiesthanWSPShearwalls (about1/3capacity)• SDPWSTable4.3C,Section4.3.7.5providescapacities&
requirements• NotpermittedinSDCEorF
WSPShearwalls OverGypsum• Fireresistanceratedwallsmayrequiregypsumboardon
eachside• SDPWSTable4.3Bprovidesshearwall capacitiesforwalls
withWSPinstalledover½“or5/8”gypsumboard• Ruleofthumb:samecapacitiesaswithoutgypsumcan
beobtainediffastenerlengthincreased(gouponenailsize;i.e.if8dwithoutgypsum,use10dwithgypsum).
WallFraming
Gypsumboardeachsideofwall
WSPinstalledovergypsum
board
WallSection
Questions?
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