Wood-FrameShearWallandDiaphragmDesign
RickyMcLain,MS,PE,SE
TechnicalDirector– WoodWorks
TexasWorkshops–December,2016
Today’sMantra
Overview
• Diaphragms• Shearwalls
DiaphragmDesign
WindLoadDistributiontoDiaphragm
WINDINTODIAPHRAGMS
WINDSURFACELOADSONWALLS
WindLoadPaths
WINDINTODIAPHRAGMSASUNIFORMLINEARLOADS
WindLoadPaths
DIAPHRAGMSSPANBETWEEN
SHEARWALLS
WINDINTOSHEARWALLSASCONCENTRATEDLOADS
StudtoDiaphragm
WINDLOAD
DIAPHRAGMSHEATHING
Floor/Roofframingperpendiculartowalls
FLOORJOIST
StudtoDiaphragm
WINDLOAD
DIAPHRAGMSHEATHING
Floor/Roofframingparalleltowalls(addblocking)
FLOORJOIST
BLOCKING
UnblockedDiaphragm
UnblockedDiaphragmCapacity
• CapacitiesinSDPWSareNominal values.NotASD
DivideNominalValuesby2.0forASDCapacityMultiplyNominalValuesby0.8forLRFDCapacity
• CapacityisreducedforspecieswithSpecificGravity<0.5• ForSprucePineFirmultiplyby0.92
BlockedDiaphragm
BlockedDiaphragmCapacity
• CapacitiesinSDPWSareNominal values.NotASD
DivideNominalValuesby2.0forASDCapacityMultiplyNominalValuesby0.8forLRFDCapacity
• CapacityisreducedforspecieswithSpecificGravity<0.5• ForSprucePineFirmultiplyby0.92
ShearWallCapacitiesinAWCSDPWS
UnblockedBlocked
DiaphragmTypes
CASE1DIAPHRAGM•HigherShearValues•Panelsperpendiculartofloorframingforimprovedperformance
CASES2-6Maybepreferredforlowsheardemandwherechangingframingdirectionhelps•HVACruns•FireBlocking/DraftStopping
RoofTrusses4x8sheathingN-S
DiaphragmTypes
SDPWSTables4.2A&B
DiaphragmAspectRatio
SDPWSTable4.2.4
CalculatingDiaphragmForces
AWCDesignAid6
MaxShearatEnds
MaxMomentatMid-Span
CalculatingDiaphragmForces
AWCDesignAid6
DiaphragmShear:• MaxShear=Diaphragm
ReactionatShearwall• DiaphragmUnitShear=
Reaction/LengthofDiaphragm=plf
CalculatingDiaphragmForces
24’
72’
Diaphragm Fastener Schedule
Zone A12’
Zone A 12’Zone B 48’
Diaphragm– BendingMember
Tensionedge
Compressionedge
CalculatingDiaphragmForces
AWCDesignAid6
DiaphragmChordForces:• MaxChordForceOccursat
LocationofMaxMoment• ChordForce=TorC• ChordForce=MMAX /
DiaphragmDepth• ChordUnitShear=ChordForce
/LengthofDiaphragm=plf
DiaphragmChords
WallTopPlatesTypicallyFunctionasBothDiaphragmChordsandDragStruts
DiaphragmBoundary
Strut
Strut
Chor
dCh
ord
Strut
Chor
d
SW1 – 10’ SW2 – 10’
SW3 – 16’
1 2 3
B
A
Strut
Stru
t
W =
200
plf
24’
80’
Reaction = 200 plf * 24’/2 = 2400 lbsDiaphragm Only at Shearwall = 2400 lbs / 16’ = 150 plf
DiaphragmBoundary
Strut
Strut
Chor
dCh
ord
Strut
Chor
d
SW1 – 10’ SW2 – 10’
SW3 – 16’
1 2 3
B
A
Strut
Stru
t
W =
200
plf
Does this mean that no drag struts are required?
24’
80’
DiaphragmBoundary
Alledgesofadiaphragmshallbesupportedbyaboundaryelement.(ASCE7-10Section11.2)
• DiaphragmBoundaryElements:• Chords,dragstruts,collectors,Shearwalls,frames
• Boundarymemberlocations:• Diaphragmandshearwall perimeters• Interioropenings• Areasofdiscontinuity• Re-entrantcorners.
AssumeBasicWindSpeed=115mphUltimate
ExposureB
DiaphragmDesign
• Capacity
Shearwall Design
• Conventional• ForceTransferAroundOpening• PerforatedShearwall
Example:RetailRestaurant
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-layerstraight lumbersheathing 2:1
Single-layerdiagonallumbersheathing 3:1
Double-layerdiagonallumbersheathing 4:1
CalculatingMWFRSWindLoads
CalculatewindpressureusingDirectionalMethod(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’
W=(9.6psf*(5’+3’)+(24.6)*3’)=150.6plfV=(150.6plf)*(84’/2)=6,325lbM=(150.6plf)*(84’2)/2=531,317lb*ftT=C=(531,317lb*ft)/(34ft)=15,627lb
νdiaphragm =6,325lb/34’=186plfνdiaphragm =15,627lb/84’=186plf
P
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
SmallOpeningsinDiaphragms
http://cwc.ca/wp-content/uploads/2013/11/Design-example-of-designing-for-openings-in-wood-diaphragm.pdf
Accountingforopeningsinshearpanels(diaphragmsandshearwalls)isacoderequirement(IBC2305.1.1)
Nocodepathforcheckingminimumsizeopeninglimit(otherthanprescriptivedesign– IBC2308.4.4.1&2308.7.6.1)
Doyouneedtoaccountfora
12”squareopeninginadiaphragm?
SmallOpeningsinDiaphragms
FPInnovationsmethodforcheckingsmallholesindiaphragms:
Recommendrunningananalysisoftheopening’seffectsonthediaphragmunlessthefollowingconditionsaremet.
Overview
• Diaphragms• Shearwalls
WindLoadscreateshear(sliding)andrackingforcesonastructure
Slidingresistedbyshearwall baseanchorageRackingresistedbyshearpanel&fasteners
Shearwall Functions
ComponentsofShearWallDesign
Collector&DragDesign
ShearWallConstruction
ShearTransferDetailing
ShearResistance
ShearWallConfigurationOptions
SolidorSegmentedWalls
PerforatedWallsForceTransferAround
OpeningsWalls
MaximumASDCapacityof870plf (Seismic)1217plf (Wind)
Useful,IfNecessary.
Shearwalls
HOLD-DOWN
WSPSHEATHING
ANCHORBOLTS
WOODSTUDS
RackedShearwall
EDGENAILINGPROVIDESRACKINGRESISTANCE
PanelFasteners
Shearwalls
ANCHORBOLTSTOFOUNDATION
PREVENTSLIDING!
Hold-DownsResistEndUplift
HOLD-DOWNS
ShearWallRequirementsinAWCSDPWS
3:5:1maxaspectratioforblockedWoodStructuralPanelShearWall.
ReductioninCapacitywhengreaterthan2:1
WoodEducation Institute
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 cementplaster 2:12
L
H
AR=H/L
WSPShearwall Capacity
• CapacitieslistedinAWC’sSpecialDesignProvisionsforWindandSeismic(SDPWS)
• Sheathedshearwallsmostcommon.Canalsousehorizontalanddiagonalboardsheathing,gypsumpanels,fiberboard,lathandplaster,andothers
• Blockedshearwallsmostcommon.SDPWShasreductionfactorsforunblockedshearwalls
• Notethatcapacitiesaregivenasnominal:mustbeadjustedbyareductionorresistancefactortodetermineallowableunitshearcapacity(ASD)orfactoredunitshearresistance(LRFD)
Shearwall Capacity- SDPWSChpt 4
Shearwall Capacity- SDPWSChpt 4
Shearwall Capacity- SDPWSChpt 4
Capacitybasedonblockedshearwall.Reducecapacitiesforunblocked
ComponentsofShearWallDesign
Holdown
Anchorage
BoundaryPosts
Compression
Tension
Shearwall HoldDowns
Source:DartDesignInc.com
Source:strongtie.com
BucketStyle
Shearwall HoldDowns
Straps
Source:strongtie.com
ComponentsofShearWallDesign
Accumulatedtensionfromframingtohardwaretoframingateachfloorlevel
1kip
2kips
3kips
7k
4k
1.5k 1.5k
1.5k
4k
4k
7k
7k
Overturningrestrained
connectionatbottomofstory
20ft
10ft,typ
DiscreteHoldown Systems
ComponentsofShearWallDesign
Collector&DragDesign
ShearWallConstruction
ShearTransferDetailing
ShearResistance
ShearTransferDetailing
Source:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample
ShearTransferDetailing
Source:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample
Designacompleteloadpath
ComponentsofShearWallDesign
Collector&DragDesign
ShearWallConstruction
ShearTransferDetailing
ShearResistance
LoadPath,LoadPath,LoadPath…
IBC1604.4Analysis. Loadeffects onstructuralmembersandtheirconnectionsshallbedeterminedbymethodsofstructuralanalysisthattakeintoaccountequilibrium,generalstability,geometriccompatibilityandbothshort- andlong-termmaterialproperties.
[…]
Anysystemormethodofconstructiontobeusedshallbebasedonarationalanalysisinaccordancewithwell-established principlesofmechanics.Suchanalysis shall resultinasystemthatprovidesacompleteloadpathcapableoftransferring loads fromtheirpointoforigintotheload-resisting elements.
Resources:
TheAnalysisofIrregularShapedDiaphragms. WhitepaperbyR.TerryMalonehttp://www.woodworks.org/wp-content/uploads/Irregular-Diaphragms_Paper1.pdf
TheAnalysisofIrregularShapedStructures. TextbookbytheR.TerryMalone
NEHRPSeismicDesignTechnicalBrief.SeismicDesignofWoodLight-FrameStructuralDiaphragmSystems:AGuideforPracticingEngineers
http://www.nehrp.gov/library/techbriefs.htm
Collector&Drag(Diaphragm)Design
RetailRestaurant– Shearwall Design
84’
34’
10’6’ 8’5’
6’
6’
6’
6’
6’4’
29’24’
10’
3’3’
P =6,325lb – fromdiaphragmcalcs usingDirectionalMethod
Let’sseewhathappenswhenweuseEnvelopeMethodtocalculateMWFRSloadstofrontshearwall
P
CalculatingMWFRSWindLoads
CalculatewindpressureusingEnvelopeMethod(ASCE7Chpt 28)
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=8.3psf wallstyp.
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
ConventionalShearwall Overturning
νshearwall =567plfHolddownsrequiredatshearwallsT=νhT=567plf*10’=5,670lb
Holddowncapacity=7,045lbManyavailableprefabricatedholddownswithcapacitieslistedbymanufacturers
34’
6’ 6’ 6’ 6’ 6’2’ 2’
10’
Hold-DownAnchor
ConventionalShearwall Overturning
νshearwall =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.
Hold-Downs:Segmentedv.Perforated
SegmentedShearwall
PerforatedShearwall
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 Capacity
Wallhas12’/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
ForceTransferAroundOpening(FTAO)
FTAOShearwalls Methodologies
• Shearwall designmethodologywhichaccountsforsheathedportionsofwallaboveandbelowopenings(perforatedneglects)
• Openingsaccountedforbyreinforcingedgesusingstrappingorframing
• SDPWS4.3.5.2providesspecificrequirements• H/Lratiodefinedbywallpier• Min.wallpierwidth=2’-0”
• Reducednumberofholddowns(onlyatendsoftotalwall)
• Thereare3mainmethodsofFTAOanalysis;SDPWSdoesnotrequireoneparticularmethodbeused,onlythatdesignis“basedonarationalanalysis”• DragStrut,CantileverBeam,&Diekmann DesignOptions
WhyUseForceTransferAroundOpenings?
Fullheightwallpiersdonotmeetmax3.5:1Ratio
8feettall2feetwide8/2=4>3.5NotAShearwall!
WhyUseForceTransferAroundOpenings?
ShorterConstrainedpiersdomeet3.5:1max
aspectratio
5feettall2feetwide5/2=2.5< 3.5CanbeaShearWall!
ReferencesforFTAODesign
APAAuthoredSEAOCPaperhttps://www.apawood.org/Data/Sites/1/documents/technicalresearch/seaoc-2015-ftao.pdf
SEAOCStructural/SeismicDesignManual,Volume2Providesnarrativeandworkedoutexample
DesignofWoodStructuresTextbookbyBreyeretal.
Double-SidedShearwalls
High-strengthwoodshearwallscanbedouble-sidedwithWSPsheathingoneachside:SDPWS4.3.3.3SummingShearCapacities:Forshearwallssheathedwiththesameconstructionandmaterialsonoppositesidesofthesamewall,thecombinednominalunitshearcapacity shallbepermittedtobetakenastwicethenominalunitshearcapacityforanequivalentshearwallsheathedononeside(4.3.5.3hasmaxcapacitiesfordouble-sidedperforatedwalls)
Double-SheathedShearwalls
Thereisalsoanoptiontohaveasinglesided,doublesheathedshearwall.
TestingandreportbyAPAconcludethatitispermissibletousethecapacityofthewallthesameasiftherewasonelayerofWSPoneachsideofthewallprovidedthatanumberofcriteriaaremetincluding:• Framingmembersatpanel
jointsare3xor2-2x• Minimumnailspacingis4”• Others
Questions?
ThisconcludesTheAmericanInstituteofArchitectsContinuingEducationSystemsCourse
RickyMcLain,MS,PE,SE
TechnicalDirector- WoodWorks
(802)498-3310
Visitwww.woodworks.org formoreeducationalmaterials,casestudies,designexamples,aprojectgallery,andmore
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