lateral design of mid-rise wood structures for wind loads

LateralDesignofMid-RiseWoodStructuresforWindLoads

PresentedbyRickyMcLain,MS,PE,SEHoustonWoodSolutionsFairSeptember14,2016

“TheWoodProductsCouncil”isaRegisteredProviderwithTheAmericanInstituteofArchitectsContinuingEducationSystems(AIA/CES),Provider#G516.

Credit(s)earnedoncompletionofthiscoursewillbereportedtoAIACESforAIAmembers.CertificatesofCompletionforbothAIAmembersandnon-AIAmembersareavailableuponrequest.

ThiscourseisregisteredwithAIACESforcontinuingprofessionaleducation.Assuch,itdoesnotincludecontentthatmaybedeemedorconstruedtobeanapprovalorendorsementbytheAIAofanymaterialofconstructionoranymethodormannerofhandling,using,distributing,ordealinginanymaterialorproduct.________________________________Questionsrelatedtospecificmaterials,methods,andserviceswillbeaddressedattheconclusionofthispresentation.

CourseDescription

Asincreasesinurbandensitybecomenecessarytoaddressgrowingpopulations,manybuildingdesignersanddevelopersareleveragingwood’sabilitytoachievemultiple,simultaneousobjectiveswithmid-risestructures—oneofwhichiseffectiveperformancewhensubjecttowindforces.Thispresentationexaminesdesignprocessesforlateralframingcomponents,whicharecriticaltothedesignofcode-compliantmid-risewoodstructuressubjecttowindloads.Topicsinthishighlytechnicalpresentationwillincludewindloadspaths,stackedmulti-storyshearwalls,accumulatedshearwallforcesanddeflections,discontinuousshearwalls,andanchorageofshearwallstoconcretepodiumslabs.

LearningObjectives

1. Reviewwindloadpathsinmulti-story,wood-framestructures.

2. Explorethedifferencesbetweenshearwallsanddiaphragmswhenstackingmultiplestoriesofwood-framelateralforce-resistingsystems.

3. Examinecommonshearwalldesignchecksforcomponentsinmulti-storybuildingsdesignedtoresistaccumulatedwindforces.

4. Demonstrateeffectivedetailingpracticesforwoodshearwalltie-downattachmentstoconcretepodiumsandfoundations.

Follow the

load

Loadpath,loadpath,loadpath!

Cables(load path)

CompleteLoadPaths

….You’retheoneinthebasket!

Multi-StoryWoodDesign

Photocredit:MattTodd&PBArchitects

Following the load…

LoadPathContinuity

Photocredit:MattTodd&PBArchitectsKaruna IHolst Architecture

Photo: Terry Malone

Multi-StoryConsiderations

• WindLoadPaths• Multi-StoryStackedShearWallEffects• AccumulationofOverturningLoads• ShearWallDeflection• DiaphragmModeling• DiscontinuousShearWalls

WindLoadDistributiontoShearwalls

Multi-StoryWindLoadDesign


DesignPrinciplesaretheSame

Rememberto:FOLLOWTHELOAD!


WINDSURFACELOADSONWALLS


WINDINTODIAPHRAGMSASUNIFORMLINEARLOADS


DIAPHRAGMSSPANBETWEEN

SHEARWALLS

WINDINTOSHEARWALLSASCONCENTRATEDLOADS


DIAPHRAGMWINDFORCESDONOTACCUMULATE-THEYAREISOLATEDATEACHLEVEL

SHEARWALLWINDFORCESDOACCUMULATE-UPPERLEVELFORCESADDTOLOWERLEVELFORCES

PublishedMulti-StoryShearWallDesignExamples

Freedownloadatwoodworks.org

SEAOCStructural/SeismicDesignManualVolume2PublishedbyICC

Multi-StoryWindDesign

ElevationSource:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample


FloorPlanSource:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample


Shearwall LayoutSource:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample

Shearwall designwe’lllookat


Shearwall LayoutSource:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample

ComponentsofShearWallDesign

Collector&DragDesign

ShearWallConstruction

ShearTransferDetailing

ShearResistance


Typ.ShearWallElevationWindForcesPerStory29’-0”

10’-0”Typ.

F5 =5.2k

F4 =3.8k

F3 =3.7k

F2 =3.6k

F1 =3.4k

FP =1.7k


Typ.ShearWallElevationAccumulatedWindForces29’-0”

10’-0”Typ.

F =5.2k

F=9k

F=12.7k

F=16.3k

F=19.7k

F=21.4k


Holdown

Anchorage

BoundaryPosts

CompressionTension

OverturningResistance

OverturningForceCalculation

F =5.2k

F=9k

F=12.7k

F=16.3k

F=19.7k

T=C=F*h/L

T&Carecumulativeatlowerstories

Lismomentarm,notentirewalllength

1.9k

5.1k

9.6k

15.4k

22.5k

h

LAssumeL=29ft-1ft=28ft

SolePlateCrushing

SolePlateCrushing

Compressionforcesperpendiculartograincancauselocalizedwoodcrushing.NDSvaluesforwithmetalplatebearingonwood resultinamaximumwoodcrushingof0.04”.Relationshipisnon-linear

SolePlateCrushing

NDSCommentaryC4.2.6:whenajointismadeoftwowoodmembersandbothareloadedperpendiculartograin,theamountofdeformationwillbeapproximately2.5timesthatofametalplatetowoodjoint.

Source:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample

CompressionPostSize&SolePlateCrush

Level Compression RequiredBearingArea

PostSize

Story SolePlateCrush

5xSolePlateCrush

5th Floor 1.9k 4.4in2 (2)-2x4 0.011” 0.057”

4th Floor 5.1k 11.9in2 (2)-4x4 0.013” 0.067”

3rd Floor 9.6 k 22.6 in2 (2)-4x4 0.034” 0.171”

2nd Floor 15.4k 36.3in2 (3)-4x4 0.039” 0.195”

1st Floor 22.5k 39.8in2 (4)-4x4 0.026” 0.13”

Floors2-5useS-P-F#2SolePlate,Fcperp =425psiFloor1useSYP#2SolePlate,Fcperp =565psi

StorytoStoryCompressionForceTransfer

Source:W

oodW

orks

Five-StoryWoo

d-Fram

eStructureoverPod

iumSlabDesignExam

ple

RimJoistBuckling&Crushing

IncreasingCompressionPostSize

Source:W

oodW

orks

Five-StoryWoo

d-Fram

eStructureoverPod

iumSlabDesignExam

ple

OverturningTension

EqualandOppositeForces

CompressionTension

UsingDeadLoadtoResistOverturning

Source:Strongtie

Deadloadfromabove(Wall,Floor,Roof)canbeusedtoresistsomeoralloverturningforces,dependingonmagnitude

LoadCombinationsofASCE7-10:06.D+0.6W

ShearWallHoldownOptions

StandardHoldownInstallationStrapHoldown

Installation

…………

………

Continuous RodTiedown Systems

6+kipstorytostorycapacities

13+kipcapacities

100+kipcapacities20+kips/level

ThreadedRodTieDownw/TakeUpDevice

Source:Strongtie Source:hardyframe.com

ThreadedRodTieDownw/oTakeUpDevice


Tensionaccumulatesinrod.Bearingplatesseelocaloverturningonly.Tensionzone

boundaryframingincompression!

ContinuousRodHoldown System

Overturningrestraintat

bearingplateattopofstory

1.9k

3.2k

4.5k

5.8k

7.1k

1.9k

5.1k

9.6k

15.4k

22.5k

F =5.2k

F=9k

F=12.7k

F=16.3k

F=19.7k

TieDownRodSize&Elongation

Level PlateHght

Tension RodDia.

Steel RodCapacity

RodElong.

5thFloor

10ft 1.9k 3/8” A36 2.4k 0.10”

4thFloor

10ft 5.1k 5/8” A36 6.7k 0.09”

3rdFloor

10ft 9.6 k 5/8” A193 14.4 k 0.18”

2ndFloor

10ft 15.4k 3/4” A193 20.7 k 0.19”

1stFloor

10ft 22.5k 7/8” A193 28.2 k 0.2”

BearingPlateCrushing

BearingPlateSize&Thickness

LevelBearingPlate Bearing

LoadAllow.BearingCapacity

BearingPlateCrush

W L T HoleArea

Abrng

5thFloor

3 in 3.5in 3/8” 0.25in2

10.25in2

1.9k 4.4k 0.012”

4thFloor

3in 3.5in 3/8” 0.518in2

9.98in2 3.2k 4.2 k 0.022”

3rdFloor

3in 5.5in 1/2” 0.518in2

15.98in2

4.5k 6.8 k 0.018”

2ndFloor

3in 5.5in 1/2” 0.69in2

15.8in2 5.8k 6.7 k 0.03”

1stFloor

3 in 8.5in 7/8” 0.89in2

24.6in2 7.0k 10.4k 0.014”

Shearwall Deformation– SystemStretch

Totalsystemstretchincludes:• RodElongation• Take-updevice

displacement• BearingPlateCrushing• SolePlateCrushing

Source:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample

AccumulativeMovement

Level RodElong.

Shrinkage SolePlateCrush

BearingPlateCrush

TakeUpDeflect.Elong.

TotalDisplac.

5thFloor

0.1” 0.03” 0.057” 0.012” 0.03” 0.23”

4thFloor

0.09” 0.03” 0.067” 0.022” 0.03” 0.24”

3rdFloor

0.18” 0.03” 0.171” 0.018” 0.03” 0.43”

2ndFloor

0.19” 0.03” 0.195” 0.03” 0.03” 0.48”

1stFloor

0.2” 0.03” 0.13” 0.014” 0.03” 0.4”

WithShrinkageCompensatingDevices

ShearWallDeflection

SDPWS2008Eq 4.3-1

SDPWS2008Eq.C4.3.2-1

Deflection

Bendingofboundaryelements

IBC2000to2015Eq.23-2

ShearWallDeflection

SDPWS2008Eq 4.3-1


Deflection

ShearDeformationofSheathingPanels&

Slipofnails@paneltopanelconnections

IBC2000to2015Eq.23-2

ShearWallDeflection

SDPWS2008Eq 4.3-1


IBC2000to2015Eq.23-2

Deflection

RigidBodyRotation

b

h

Δa

Shearwall Deflection

Level UnitShear

EndPostA

EndPostE

Ga TotalDisplace.

Deflection

5thFloor

179plf 10.5in2 1400ksi

10k/in 0.23” 0.26”

4thFloor

310plf 24.5in2 1400ksi

10k/in 0.24” 0.4”

3rdFloor

438plf 24.5in2 1400ksi

10k/in 0.43” 0.59”

2ndFloor

562plf 36.8in2 1400ksi

13k/in 0.48” 0.6”

1stFloor

679plf 49in2 1400ksi

13k/in 0.4” 0.67”

Shearwall DeflectionMethods

Multiplemethodsforcalculatingaccumulativeshearwall deflectionexistMechanicsBasedApproach:• Usessinglestorydeflection

equationateachfloor• Includesrotational&crushing

effects• UsesSDPWS3partequation

Othermethodsexistwhichusealternatedeflectionequations,FEM

Shearwall DeflectionCriteriaforWind

Unlikeseismic,nocodeinformationexistsondeflection/driftcriteriaofstructuresduetowindloads

Serviceabilitychecktominimizedamagetocladdingandnonstructuralwalls

ASCE7-10:C.2.2DriftofWallsandFrames.Lateraldeflectionordriftofstructuresanddeformationofhorizontaldiaphragmsandbracingsystemsduetowindeffectsshallnotimpairtheserviceabilityofthestructure.

Whatwindforceshouldbeused?Whatdriftcriteriashouldbeapplied?

Allowable=?

Shearwall DeflectionCriteriaforWind

WindForcesConsensusisthatASDdesignlevelforcesaretooconservativeforbuilding/framedriftcheckduetowind• CommentarytoASCE7-10AppendixCsuggeststhatsome

recommendusing10yearreturnperiodwindforces:• ~70%of700returnperiodwind(ultimatewindspeed

forriskcategoryIIbuildings)• Others(AISCDesignGuide3)recommendusing75%of50

yearreturnperiodforces

DriftCriteriaCanvarywidelywithbrittlenessoffinishesbutgenerallyrecommendationsareintherangeofH/240toH/600

DiaphragmModelingMethods

Possible Shear Wall Layouts

Typical Unit

7654321

D

C

B

A

NotusingallsharedwallsforShear

RobustDiaphragmAspectRatio

DiaphragmModelingMethods


Typical Unit

7654321

D

C

B

A

Butmaybenotmuchwallavailableonexterior

RobustDiaphragmAspectRatio

LightFrameWoodDiaphragmsoftendefaulttoFlexibleDiaphragms

CodeBasis:ASCE7-1026.2Definitions(Wind)Diaphragmsconstructedofwoodstructuralpanelsarepermittedtobeidealizedasflexible

CodeBasis:ASCE7-1012.3.1.1(Seismic)Diaphragmsconstructedofuntopped steeldeckingorwoodstructuralpanelsarepermittedtobeidealizedasflexible ifanyofthefollowingconditionsexist:[…]c.Instructuresoflight-frameconstructionwhereallofthefollowingconditionsaremet:

1.Toppingofconcreteorsimilarmaterials isnotplacedoverwoodstructuralpaneldiaphragmsexceptfornonstructuraltoppingnogreaterthan11/2in.thick.2.Eachlineofverticalelementsoftheseismic forceresistingsystemcomplieswiththeallowablestorydriftofTable12.12-1..

RigidorFlexibleDiaphragm?

Hypothetical FlexibleDiaphragm Distribution

Typical Unit

7654321

D

C

B

A

Areatributarytocorridorwallline

Areatributarytoexteriorwall

line

23%

23%

27%27%

Largeportionofloadonlittle

wall

Changing wall construction does NOT impact load to wall line

Hypothetical RigidDiaphragm Distribution

Typical Unit

7654321

D

C

B

A

Longer,stifferwallsreceivemoreload

Diaphragmassumedtoberigidbody.

10%

10%

40%40%

Narrow,flexiblewallsreceiveless

load

Changing wall construction impacts load to wall line

ASCE7-1012.3.1.3(Seismic)

[Diaphragms]arepermittedtobeidealizedasflexiblewherethecomputedmaximum in-planedeflectionofthediaphragmunderlateralloadismorethantwotimestheaveragestorydriftofadjoiningverticalelementsoftheseismic force-resistingsystemoftheassociatedstoryunderequivalent

tributarylateralloadasshowninFig.12.3-1.

IBC2012Chapter2Definition(Wind&Seismic)

Adiaphragmisrigid forthepurposeofdistributionofstoryshearandtorsionalmomentwhenthelateraldeformationofthediaphragmislessthanorequaltotwotimestheaveragestorydrift.

CanaRigidDiaphragmbeJustified?

Average drift of walls

Maximum diaphragm deflection

SomeAdvantagesofRigidDiaphragm

• Moreload(plf)tolongerinterior/corridorwalls• Lessload(plf)tonarrowwallswhereoverturningrestraintistougher• Cantuneloadstowallsandwalllinesbychangingstiffnessofwalls

SomeDisadvantagesofRigidDiaphragm

• Considerationsoftorsionalloadingnecessary• Morecomplicatedcalculationstodistributeloadtoshearwalls• Mayunderestimate“Real”loadstonarrowexteriorwalls• Justificationofrigidassumption

RigidDiaphragmAnalysis

Semi-RigidDiaphragmAnalysis

• Neitheridealizedflexiblenoridealizedrigid• Explicitmodelingofdiaphragmdeformationswithshearwalldeformationstodistributelateralloads

• Noteasy.

EnvelopingMethod

• IdealizedasBOTHflexibleandrigid.• Individualcomponentsdesignedforworstcasefromeachapproach• Beenaroundawhile,officiallyrecognizedinthe2015SDPWS

TwoMoreDiaphragmApproaches


Typical Unit

7654321

D

C

B

A

TheCantileverDiaphragmOption


Typical Unit

7654321

D

C

B

A

RobustAspectRatiobutonlysupportedon3sides…

OpenFrontStructure CantileverDiaphragm

CantileveredDiaphragmsinSDPWS2008

AWCSDPWS2008Figure4AAWCSDPWS2008Figure4B

OpenFrontStructureSDPWS4.2.5.1.1L≤25ftL/W≤1,onestory

≤2/3,multi-story


Exception:Wherecalculationsshowthediaphragmdeflectionscanbetolerated,thelength,L,canbeincreasedtoL/W≤1.5forWSPsheatheddiaphragms.

CantileveredDiaphragmSDPWS4.2.5.2Lc ≤25ftLc/W≤2/3



Typical Unit

7654321

D

C

B

A

OpenFrontStructureorCantileveredDiaphragm?


OpenFrontStructurewithaCantileveredDiaphragm

AWCSDPWS2015Figure4A

CantileveredDiaphragm SDPWS4.2.5.2L’/W’≤1.5WhenTorsionally Irregular

L’/W’≤1,onestory2/3,multi-story

L’≤35 ft

OpenFrontStructure&CantileveredDiaphragmsinSDPWS2015

Provideddiaphragmsmodelledasrigidorsemi-rigidandforseismic,thestorydriftateachedgeofthestructurewithinallowablestorydriftofASCE7.Storydriftsincludetorsionandaccidentaltorsionalloadsanddeformationsofthediaphragm.

CantileveredDiaphragm SDPWS4.2.5.2L’/W’≤1.5WhenTorsionally Irregular

L’/W’≤1,onestory≤2/3,multi-story

L’≤35 ft

OpenFrontStructure&CantileveredDiaphragmsinSDPWS2015

IfL’≤6ft ,sectiondoesn’tapply.Exception:

TieDownAttachmenttoConcrete

Source:Strongtie

TieDownBoltwithWasher

Source:Strongtie

TieDownBoltwithWasher- Reinforcing

Source:Strongtie

TieDownAnchorChairinCastSlab

Source:EarthboundAnchors

EmbeddedSteelPlates– WeldonRods

TieDownAnchors– PrecastThroughBolt

TieDownAnchors– ThroughPodium

LateralLoadPathContinuity:WallElevation

ShearWall

ShearWall

Header

Header

Headerdistributesuppershearwall

endpostconcentrated load

towallbelowHeaderalso

distributes uppershearwallshearto

wallbelow

Postsinlowerwalltransfer

upperwallendpost

concentratedloadsto

foundation

Wallplatesactasdragstrutstotransfershearloadsfromupperwalltolowerwall

Note:anymembersupportingadiscontinuous wallmustbedesigned fortheover-strengthfactorunderASCE7-10Section12.3.3.3,forSDCB-F

OffsetShearWallOverturningResistance

Source:Strongtie

TieDowntoSteelBeamAttachment

Source:Strongtie

Recap

• WindLoadPaths• Multi-StoryStackedShearWallEffects• AccumulationofOverturningLoads• ShearWallDeflection• DiaphragmModeling• DiscontinuousShearWalls

Questions?

ThisconcludesTheAmericanInstituteofArchitectsContinuingEducationSystemsCourse

RickyMcLain,MS,PE,SE

[email protected](802)498-3310

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

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lateral design of mid-rise wood structures for wind loads

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