Wood-Frame Shear Wall and Diaphragm · PDF fileWood-Frame Shear Wall and Diaphragm Design...

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

Ricky.McLain@WoodWorks.org

(802)498-3310

Visitwww.woodworks.org formoreeducationalmaterials,casestudies,designexamples,aprojectgallery,andmore

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