Lateral Design of Mid- Rise Wood Structures for Wind … Design of Mid-Rise Wood Structures for Wind...

LateralDesignofMid-RiseWoodStructuresforWindLoads

PresentedbyRickyMcLain,MS,PE,SEPhiladelphiaWood Solutions FairOctober13,2016

“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.

Insert picture of me graduating college

Follow the

load

Multi-StoryWoodDesign

Photocredit:MattTodd&PBArchitects

Following the load…

LoadPathContinuity

Photocredit:MattTodd&PBArchitectsKaruna IHolst Architecture

Photo: Terry Malone

Multi-StoryConsiderations

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

WindLoadDistributiontoShearwalls

WindLoadDistributiontoShearwalls

WindLoadDistributiontoShearwalls

Photocredit:MattTodd&PBArchitects

Multi-StoryWindLoadDesign

Photocredit:MattTodd&PBArchitects

DesignPrinciplesaretheSame

Rememberto:FOLLOWTHELOAD!

Multi-StoryWindLoadDesign

WINDSURFACELOADSONWALLS

Multi-StoryWindLoadDesign

WINDINTODIAPHRAGMSASUNIFORMLINEARLOADS

Multi-StoryWindLoadDesign

DIAPHRAGMSSPANBETWEEN

SHEARWALLS

WINDINTOSHEARWALLSASCONCENTRATEDLOADS

Multi-StoryWindLoadDesign

DIAPHRAGMWINDFORCESDONOTACCUMULATE-THEYAREISOLATEDATEACHLEVEL

SHEARWALLWINDFORCESDO ACCUMULATE-UPPERLEVELFORCESADDTOLOWERLEVELFORCES

DesignExample:FiveOverOneWoodFrame

Freedownloadatwoodworks.org

Multi-StoryWindDesign

FloorPlanSource:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample

Multi-StoryWindDesign

Shearwall LayoutSource:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample

Shearwall designwe’lllookat

Multi-StoryWindDesign

Shearwall LayoutSource:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample

ComponentsofShearWallDesign

Typ.ShearWallElevationWindForcesPerStory29’-0”

10’-0”Typ.

F5 =5.2k

F4 =3.8k

F3 =3.7k

F2 =3.6k

F1 =3.4k

ComponentsofShearWallDesign

Typ.ShearWallElevationAccumulatedWindForces29’-0”

10’-0”Typ.

F =5.2k

F=9k

F=12.7k

F=16.3k

F=19.7k

ComponentsofShearWallDesign

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

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-StoryWood-Fram

eStructureoverPodiumSlabDe

signExam

ple

RimJoistBuckling&Crushing

IncreasingCompressionPostSize

Source:W

oodW

orks

Five-StoryWood-Fram

eStructureoverPodiumSlabDe

signExam

ple

OverturningTension

EqualandOppositeForces

CompressionTension

UsingDeadLoadtoResistOverturning

Source:Strongtie

Deadloadfromabove(Wall,Floor,Roof)canbeusedtoresistsomeoralloverturningforces,dependingonmagnitude

LoadCombinationsofASCE7-10:06.D+0.6W

ShearWallHoldown Options

StandardHoldownInstallationStrapHoldown

Installation

…………

………

Continuous RodTiedown Systems

6+kipstorytostorycapacities

13+kipcapacities

100+kipcapacities20+kips/level

ComponentsofShearWallDesign

Tensionaccumulatesinrod.Bearingplatesseelocaloverturningonly.Tensionzone

boundaryframingincompression!

Continuous RodHoldown 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

ThreadedRodTieDownw/TakeUpDevice

Source:Strongtie Source:hardyframe.com

ThreadedRodTieDownw/oTakeUpDevice

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

SDPWS2008Eq.C4.3.2-1

Deflection

ShearDeformationofSheathingPanels&

Slipofnails@paneltopanelconnections

IBC2000to2015Eq.23-2

ShearWallDeflection

SDPWS2008Eq 4.3-1

SDPWS2008Eq.C4.3.2-1

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

Possible Shear Wall Layouts

Typical Unit

7654321

D

C

B

A

Butmaybenotmuchwallavailableonexterior

RobustDiaphragmAspectRatio

LightFrameWoodDiaphragmsoftendefaulttoFlexibleDiaphragms

CodeBasis:ASCE7-1026.2Definitions(Wind)Diaphragmsconstructedofwoodstructuralpanelsarepermittedtobeidealizedasflexible

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

1.Toppingofconcreteorsimilarmaterialsisnotplacedoverwoodstructuralpaneldiaphragmsexceptfornonstructural toppingnogreaterthan11/2in.thick.2.EachlineofverticalelementsoftheseismicforceresistingsystemcomplieswiththeallowablestorydriftofTable12.12-1..

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]arepermittedtobeidealizedasflexible wherethecomputedmaximumin-planedeflectionofthediaphragmunderlateralloadismorethantwotimestheaveragestorydriftofadjoiningverticalelementsoftheseismicforce-resistingsystemoftheassociatedstoryunderequivalenttributarylateralloadasshowninFig.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

Possible Shear Wall Layouts

Typical Unit

7654321

D

C

B

A

TheCantileverDiaphragmOption

Possible Shear Wall Layouts

Typical Unit

7654321

D

C

B

A

RobustAspectRatiobutonlysupportedon

3sides…

OpenFrontStructure CantileverDiaphragm

CantileveredDiaphragmsinSDPWS2008

AWCSDPWS2008Figure4AAWCSDPWS2008Figure4B

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

≤2/3,multi-story

CantileveredDiaphragmsinSDPWS2008

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

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

CantileveredDiaphragmsinSDPWS2008

Possible Shear Wall Layouts

Typical Unit

7654321

D

C

B

A

OpenFrontStructureorCantileveredDiaphragm?

CantileveredDiaphragmsinSDPWS2015

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.

WindLoadDistributiontoShearwalls

TieDownAttachmenttoConcrete

Source:Strongtie

TieDownBoltwithWasher

Source:Strongtie

TieDownBoltwithWasher- Reinforcing

Source:Strongtie

EmbeddedSteelPlates– WeldonRods

TieDownAnchors– PrecastThroughBolt

TieDownAnchors– ThroughPodium

DiscontinuousShearWalls

Photocredit:MattTodd&PBArchitectsKaruna IHolst Architecture

Photo: Terry Malone

OffsetShearWallOverturningResistance

Source:Strongtie

TieDowntoSteelBeamAttachment

Source:Strongtie

TieDowntoSteelBeamAttachment

Recap

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

Questions?

ThisconcludesTheAmericanInstituteofArchitectsContinuingEducationSystemsCourse

RickyMcLain,MS,PE,SE

WoodWorksRicky.McLain@WoodWorks.org(802)498-3310

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

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