wood-frame shear wall and diaphragm design · maximum shear wall dimension ratios see sdpws table...

Wood-FrameShearWallandDiaphragmDesign

RickyMcLain,MS,PE,SE

TechnicalDirector– WoodWorks

ChicagoAreaWorkshops – April, 2017

Overview

• Diaphragms

• Shearwalls

DiaphragmDesign

WindLoadDistributiontoDiaphragm

WINDINTODIAPHRAGMS

WINDSURFACELOADSONWALLS

WindLoadPaths

WINDINTODIAPHRAGMSASUNIFORMLINEARLOADS

WindLoadPaths

DIAPHRAGMSSPANBETWEEN

SHEARWALLS

WINDINTOSHEARWALLSASCONCENTRATEDLOADS

StudtoDiaphragm

WINDLOAD

DIAPHRAGMSHEATHING

Floor/Roofframing

perpendiculartowalls

FLOORJOIST

StudtoDiaphragm

WINDLOAD

DIAPHRAGMSHEATHING

Floor/Roofframing

paralleltowalls(addblocking)

FLOORJOIST

BLOCKING

CalculatingDiaphragmForces

AWCDesignAid6

MaxShearatEnds

MaxMoment

atMid-Span

CalculatingDiaphragmForces

AWCDesignAid6

DiaphragmShear:• MaxShear=Diaphragm

ReactionatShearwall• DiaphragmUnitShear=

Reaction/LengthofDiaphragm=plf

UnblockedDiaphragm

UnblockedDiaphragmCapacity

• CapacitiesinSDPWSareNominal values.NotASDDivideNominalValuesby2.0forASDCapacity

MultiplyNominalValuesby0.8forLRFDCapacity

• CapacityisreducedforspecieswithSpecificGravity<0.5

• ForSprucePineFirmultiplyby0.92

BlockedDiaphragm

BlockedDiaphragmCapacity

• CapacitiesinSDPWSareNominal values.NotASDDivideNominalValuesby2.0forASDCapacity

MultiplyNominalValuesby0.8forLRFDCapacity

• CapacityisreducedforspecieswithSpecificGravity<0.5

• ForSprucePineFirmultiplyby0.92

ShearWallCapacitiesinAWCSDPWS

UnblockedBlocked

DiaphragmTypes

CASE1DIAPHRAGM

•HigherShearValues•Panelsperpendiculartofloorframingfor

improvedperformance

CASES2-6Maybepreferred

forlowsheardemandwhere

changingframingdirection

helps

•HVACruns•FireBlocking/DraftStopping

RoofTrusses4x8sheathingN-S

DiaphragmTypes

SDPWSTables4.2A&B

DiaphragmAspectRatio

SDPWSTable4.2.4

CalculatingDiaphragmForces

24’

72’

Diaphragm Fastener Schedule

Zone A12’

Zone A 12’Zone B 48’

Diaphragm– BendingMember

Tensionedge

Compressionedge

DiaphragmChordForces

AWCDesignAid6

DiaphragmChordForces:• MaxChordForceOccursat

LocationofMaxMoment• ChordForce=TorC• ChordForce=MMAX /

DiaphragmDepth• ChordUnitShear=ChordForce

/LengthofDiaphragm=plf

DiaphragmChords

WallTopPlatesTypicallyFunctionasBothDiaphragmChordsandDragStruts

DiaphragmBoundary

Strut

Strut

Cho

rdC

hord

Strut

Cho

rd

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

Cho

rdC

hord

Strut

Cho

rd

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– DiaphragmDesignCriticalShearwall 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

Atparapetswindward

andleewardpressures

occuroneachparapet.

Section27.4.5:Pp =q(GCpn)GCpn =1.5Windwardparapet,-1.0LeewardparapetWindwardParapetGCpf is1.5:16.4*1.5*0.6=14.76psf

LeewardParapetGCpf is1.0:16.4*1.0*0.6=9.84psf

NetParapet=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)/8=132,829lb*ft

T=C=(132,829lb*ft)/(34ft)=3,907lb

νdiaphragm =6,325lb/34’=186plfνdiaphragm =3,907lb/84’=47plf

P

DiaphragmCapacity:SDPWSTable4.2C

PANEL

GRADE

COMMON

NAILSIZE

ORSTAPLEf

LENGTHANDGAGE

MINIMUM

FASTENER

PENETRATION

INFRAMING

MINIMUM

PANEL

THIICKNESS

MINIMUM

NOMINALWIDTHOFFRAMINGMEMBERSAT

ADJOININGPANELEDGESAND

BOUNDARIESg

NAIL

SPACING

ATALL

PANEL

EDGES

Case1

(Nounblocked

edgesor

continuous

jointsparallelto

load)

Allother

configurations

(Cases2,3,4,5

and6)

Sheathing

&single

floor

8d(2½“x

0.131”)

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(diaphragmsandshear

walls)isacoderequirement(IBC2305.1.1)

Nocodepathforcheckingminimumsizeopeninglimit(otherthan

prescriptivedesign– 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

ComponentsofShearWallDesignCollector&Drag

Design

ShearWallConstruction

ShearTransferDetailing

ShearResistance

ShearWallConfigurationOptions

SolidorSegmentedWalls

PerforatedWallsForceTransferAround

OpeningsWalls

MaximumASDCapacityof870plf (Seismic)1217plf (Wind)

Useful,If Necessary.

Shearwalls

HOLD-DOWN

WSPSHEATHING

ANCHORBOLTS

WOODSTUDS

RackedShearwall

EDGENAILINGPROVIDESRACKINGRESISTANCE

PanelFasteners

Shearwalls

ANCHORBOLTSTOFOUNDATION

PREVENTSLIDING!

Hold-DownsResistEndUplift

HOLD-DOWNS

ShearWallRequirementsinAWCSDPWS

3:5:1maxaspectratioforblockedWoodStructural PanelShearWall.

Reduction inCapacitywhengreaterthan2:1

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’sSpecialDesign

ProvisionsforWindandSeismic(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

Straps

Source:strongtie.com

Shearwall HoldDowns

Source:DartDesignInc.com

Source:strongtie.com

BucketStyle

ComponentsofShearWallDesign

Accumulatedtensionfromframingtohardwaretoframingateachfloorlevel

1kip

2kips

3kips

7k

4k

1.5k 1.5k

1.5k

4k

4k

7k

7k

Overturningrestrained

connectionatbottomofstory

20ft

10ft,typ

DiscreteHoldown Systems

ComponentsofShearWallDesignCollector&Drag

Design

ShearWallConstruction

ShearTransferDetailing

ShearResistance

ShearTransferDetailing

Source:WoodWorks Five-Story

Wood-Frame Structureover

PodiumSlabDesignExample

ShearTransferDetailing

Source:WoodWorks Five-StoryWood-Frame

StructureoverPodiumSlabDesignExample

Designacompleteloadpath

ComponentsofShearWallDesign

Collector&DragDesign

ShearWallConstruction

ShearTransferDetailing

ShearResistance

LoadPath,LoadPath,LoadPath…IBC1604.4Analysis. Loadeffectsonstructuralmembersandtheirconnectionsshallbe

determinedbymethodsofstructuralanalysisthattakeintoaccountequilibrium, general stability,

geometriccompatibilityandbothshort- andlong-termmaterialproperties.

[…]

Anysystemormethodofconstructiontobeusedshallbebasedonarationalanalysisin

accordancewithwell-established principlesofmechanics.Suchanalysisshallresultinasystemthatprovidesacompleteloadpathcapableoftransferringloadsfromtheirpointoforigintotheload-resistingelements.

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

CalculatingMWFRSWindLoadsCalculatewindpressureusingEnvelopeMethod(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=8.3psfwallstyp.

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

Atparapetswindward

andleewardpressures

occuroneachparapet.

Section28.4.2:Pp =q(GCpn)GCpn =1.5Windwardparapet,-1.0LeewardparapetWindwardParapetGCpf is1.5:20.14*1.5*0.6=18.12psf

LeewardParapetGCpf is1.0:20.14*1.0*0.6=12.08psf

NetParapet=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=1540plf

AdjustedASDCapacity =(1370plf)(0.92)/2=630plf630plf >567plf,OK

8dnailsat3”o.c.acceptable

PANELGRADE FASTENER

TYPE&

SIZE

MINIMUM

PANEL

THIICKNESS

MINIMUM

FASTENER

PENETRATION

INFRAMING

NAIL SPACING

ATALLPANEL

EDGES

PANEL EDGE

FASTENERSPACING

Wood Structural

Panels–

Sheathing

8d(2½“x

0.131”)

15/32” 13/8” 3IN. 980(Seismic)

1370(Wind)

SDPWSTable4.3A

ConventionalShearwall Overturning

νshearwall =567plfHolddownsrequiredatshearwalls

T=νhT=567plf*10’=5,670lb

Holddowncapacity=7,045lbManyavailableprefabricatedholddownswithcapacitieslistedbymanufacturers

34’

6’ 6’ 6’ 6’ 6’2’ 2’

10’

Hold-DownAnchor

ConventionalShearwall Overturningνshearwall =567plfPostsarealsorequiredatendsofthewalltoresistcompressionforces

C=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.PerforatedSegmentedShearwall

PerforatedShearwall

PerforatedShearWallMethod

HOLDDOWNSATENDOF

WALL

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;OK

Useonlyfullheightsheathedsectionstoresistshear

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=1790plf

AdjustedASDCapacity=(1790plf)(0.92)(0.75)/2=618plf618plf >567plf,OK8dnailsat2”o.c.acceptableforperforatedwall

PANELGRADE FASTENER

TYPE&

SIZE

MINIMUM

PANEL

THIICKNESS

MINIMUM

FASTENER

PENETRATION

INFRAMING

NAIL SPACING

ATALLPANEL

EDGES

PANEL EDGE

FASTENERSPACING

Wood Structural

Panels–

Sheathing

8d(2½“x

0.131”)

15/32” 13/8” 2IN. 1280(Seismic)

1790(Wind)

SDPWSTable4.3A

PerforatedShearwall Overturning

34’

6’ 6’ 6’ 6’ 6’2’ 2’

10’

νshearwall =567plfHolddownsrequiredatendsofperforatedwall

T=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,usesamemagnitudeforuniformupliftatfullheightsegmentsOneoptionistouseanchorboltswithlargewasherstoresistupliftin

bearingIfnetwasherarea=8in2,canresist(565psi)(8in2)=4,520lb inuplift

• Max.anchorboltspacing=4,520lb/756plf =5’-11”o.c.• Willalsoneedtocheckshearloadsonanchorboltsforcontrolling

case

ForceTransferAroundOpening(FTAO)

FTAOShearwalls Methodologies• Shearwall designmethodologywhichaccountsforsheathed

portionsofwallaboveandbelowopenings(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

10feettall

2feetwide

10/2=5>3.5

NotAShearwall!

WhyUseForceTransferAroundOpenings?

ShorterConstrainedpiersdomeet3.5:1max

aspectratio

5feettall

2feetwide

5/2=2.5< 3.5

CanbeaShearWall!

ReferencesforFTAODesign

APAAuthoredSEAOCPaperhttps://www.apawood.org/Data/Sites/1/documents/technicalresearch/seaoc-2015-ftao.pdf

SEAOCStructural/SeismicDesignManual,Volume2Providesnarrativeandworked outexample

DesignofWoodStructuresTextbookbyBreyeretal.

Double-SidedShearwalls

High-strengthwoodshearwallscanbedouble-sidedwithWSPsheathingoneachside:

SDPWS4.3.3.3SummingShearCapacities:Forshearwallssheathedwiththesameconstructionandmaterialsonoppositesidesofthesamewall,thecombinednominalunitshearcapacity shallbepermittedtobetakenastwicethenominalunitshearcapacityforanequivalentshearwallsheathedononeside(4.3.5.3hasmaxcapacitiesfordouble-sidedperforatedwalls)

Double-SheathedShearwalls

Thereisalsoanoptiontohaveasinglesided,doublesheathedshearwall.

TestingandreportbyAPAconcludethatitispermissibletousethecapacityofthewallthesameasiftherewasonelayerofWSPoneachsideofthewallprovidedthatanumberofcriteriaaremetincluding:

• Framingmembersatpaneljointsare3xor2-2x

• 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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