multi-story lateral design - woodworks · multi-story wind load design diaphragm wind forces do not...

LateralDesignofMid-RiseWoodStructures

PresentedbyRickyMcLain,MS,PE,SE

TechnicalDirector– WoodWorks

TexasWorkshops–December,2016

Insert picture of me graduating college

Follow the

load

Multi-StoryWoodDesign

Photocredit:MattTodd&PBArchitects

Following the load…

LoadPathContinuity


Karuna 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

SHEARWALLWINDFORCESDO ACCUMULATE-UPPERLEVELFORCESADDTOLOWERLEVELFORCES

DesignExample:FiveOverOneWoodFrame

Freedownloadat

woodworks.org

Multi-StoryWindDesign

FloorPlan

Source:WoodWorks Five-StoryWood-Frame

StructureoverPodiumSlabDesignExample


Shearwall Layout



Shearwall design

we’lllookat


Shearwall Layout



ComponentsofShearWallDesign

Typ.ShearWallElevation

WindForcesPerStory29’-0”

10’-0”Typ.

F

5

=5.2k

F

4

=3.8k

F

3

=3.7k

F

2

=3.6k

F

1

=3.4k


Typ.ShearWallElevation

AccumulatedWindForces29’-0”

10’-0”Typ.

F =5.2k

F=9k

F=12.7k

F=16.3k

F=19.7k


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

Compressionforcesperpendiculartograincancauselocalized

woodcrushing.NDSvaluesforwithmetalplatebearing

onwood resultinamaximumwoodcrushingof0.04”.

Relationshipisnon-linear

CompressionPostSize&SolePlateCrush

Level Compression RequiredBearingArea

PostSize

Story SolePlateCrush

5xSolePlateCrush

5

th

Floor 1.9k 4.4in

2

(2)-2x4 0.011” 0.057”

4

th

Floor 5.1k 11.9in

2

(2)-4x4 0.013” 0.067”

3

rd

Floor 9.6 k 22.6 in

2

(2)-4x4 0.034” 0.171”

2

nd

Floor 15.4k 36.3in

2

(3)-4x4 0.039” 0.195”

1

st

Floor 22.5k 39.8in

2

(4)-4x4 0.026” 0.13”

Floors2-5useS-P-F#2SolePlate,F

cperp

=425psi

Floor1useSYP#2SolePlate,F

cperp

=565psi

StorytoStoryCompressionForceTransfer

Source:WoodWorksFive-StoryWood-Frame


RimJoistBuckling&Crushing

IncreasingCompressionPostSize

Source:WoodWorksFive-StoryWood-Frame


OverturningTension

EqualandOppositeForces

CompressionTension

UsingDeadLoadtoResistOverturning

Source:Strongtie

Deadloadfromabove

(Wall,Floor,Roof)canbe

usedtoresistsomeorall

overturningforces,

dependingonmagnitude

Load

Combinationsof

ASCE7-10:

06.D+0.6W

ShearWallHoldown Options

StandardHoldownInstallationStrapHoldown

Installation

…………

………

Continuous RodTiedown Systems

6+kipstorytostorycapacities

13+kipcapacities

100+kipcapacities20+kips/level


Tensionaccumulatesinrod.Bearingplatesseelocaloverturningonly.Tensionzone

boundaryframingincompression!

ContinuousRodHoldownSystem

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.

5

th

Floor

10ft 1.9k 3/8” A36 2.4k 0.10”

4

th

Floor

10ft 5.1k 5/8” A36 6.7k 0.09”

3

rd

Floor

10ft 9.6 k 5/8” A193 14.4 k 0.18”

2

nd

Floor

10ft 15.4k 3/4” A193 20.7 k 0.19”

1

st

Floor

10ft 22.5k 7/8” A193 28.2 k 0.2”

BearingPlateCrushing

BearingPlateSize&Thickness

LevelBearingPlate Bearing

LoadAllow.BearingCapacity

BearingPlateCrush

W L T Hole

Area

A

brng

5

th

Floor

3 in 3.5in 3/8” 0.25

in

2

10.25

in

2

1.9k 4.4k 0.012”

4

th

Floor

3in 3.5in 3/8” 0.518

in

2

9.98in

2

3.2k 4.2 k 0.022”

3

rd

Floor

3in 5.5in 1/2” 0.518

in

2

15.98

in

2

4.5k 6.8 k 0.018”

2

nd

Floor

3in 5.5in 1/2” 0.69

in

2

15.8in

2

5.8k 6.7 k 0.03”

1

st

Floor

3 in 8.5in 7/8” 0.89

in

2

24.6in

2

7.0k 10.4k 0.014”

Shearwall Deformation– SystemStretch

Totalsystemstretch

includes:

• RodElongation

• Take-updevice

displacement

• BearingPlateCrushing

• SolePlateCrushing



AccumulativeMovement

Level RodElong.

Shrinkage SolePlateCrush

BearingPlateCrush

TakeUpDeflect.Elong.

TotalDisplac.

5

th

Floor

0.1” 0.03” 0.057” 0.012” 0.03” 0.23”

4

th

Floor

0.09” 0.03” 0.067” 0.022” 0.03” 0.24”

3

rd

Floor

0.18” 0.03” 0.171” 0.018” 0.03” 0.43”

2

nd

Floor

0.19” 0.03” 0.195” 0.03” 0.03” 0.48”

1

st

Floor

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

5

th

Floor

179plf 10.5in

2

1400

ksi

10k/in 0.23” 0.26”

4

th

Floor

310plf 24.5in

2

1400

ksi

10k/in 0.24” 0.4”

3

rd

Floor

438plf 24.5in

2

1400

ksi

10k/in 0.43” 0.59”

2

nd

Floor

562plf 36.8in

2

1400

ksi

13k/in 0.48” 0.6”

1

st

Floor

679plf 49in

2

1400

ksi

13k/in 0.4” 0.67”

Shearwall DeflectionMethods

Multiplemethodsforcalculating

accumulativeshearwall deflection

exist

MechanicsBasedApproach:

• Usessinglestorydeflection

equationateachfloor

• Includesrotational&crushing

effects

• UsesSDPWS3partequation

Othermethodsexistwhichuse

alternatedeflectionequations,FEM

Shearwall DeflectionCriteriaforWind

Unlikeseismic,nocodeinformationexistson

deflection/driftcriteriaofstructuresduetowindloads

Serviceabilitychecktominimizedamagetocladdingand

nonstructuralwalls

ASCE7-10:C.2.2DriftofWallsandFrames.Lateraldeflectionordriftofstructuresanddeformationofhorizontaldiaphragmsandbracingsystemsduetowindeffectsshallnotimpairtheserviceabilityofthestructure.

Whatwindforceshouldbeused?Whatdriftcriteriashouldbeapplied?

Allowable=?

Shearwall DeflectionCriteriaforWind

WindForcesConsensusisthatASDdesignlevelforcesaretooconservative

forbuilding/framedriftcheckduetowind

• CommentarytoASCE7-10AppendixCsuggeststhatsome

recommendusing10yearreturnperiodwindforces:

• ~70%of700returnperiodwind(ultimatewindspeed

forriskcategoryIIbuildings)

• Others(AISCDesignGuide3)recommendusing75%of50

yearreturnperiodforces

DriftCriteriaCanvarywidelywithbrittlenessoffinishesbutgenerally

recommendationsareintherangeofH/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 steeldeckingorwoodstructuralpanelsarepermittedtobeidealizedasflexibleifanyofthefollowingconditionsexist:[…]c.Instructuresoflight-frameconstructionwhereallofthefollowingconditionsaremet:

1.Toppingofconcreteorsimilarmaterialsisnotplacedoverwoodstructuralpaneldiaphragmsexceptfornonstructuraltoppingnogreaterthan11/2in.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]arepermittedtobeidealizedasflexiblewherethecomputedmaximumin-planedeflectionofthediaphragmunderlateralloadismorethantwotimestheaveragestorydriftofadjoiningverticalelementsoftheseismicforce-resistingsystemoftheassociatedstoryunderequivalenttributarylateralloadasshowninFig.12.3-1.

IBC2012Chapter2Definition(Wind&Seismic)

Adiaphragm isrigid forthepurposeofdistribution ofstoryshearandtorsionalmomentwhenthelateraldeformationofthediaphragmislessthanorequaltotwotimestheaveragestorydrift.

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

• Explicitmodelingofdiaphragmdeformationswithshearwall

deformationstodistributelateralloads

• 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

AWCSDPWS2008Figure4A

AWCSDPWS2008Figure4B

OpenFrontStructure

SDPWS4.2.5.1.1

L≤25ft

L/W≤1,onestory

≤2/3,multi-story


Exception:Wherecalculationsshowthediaphragm

deflectionscanbetolerated,thelength,L,canbe

increasedtoL/W≤1.5forWSPsheatheddiaphragms.

CantileveredDiaphragm

SDPWS4.2.5.2

Lc ≤25ft

Lc/W≤2/3



Typical Unit

7654321

D

C

B

A

OpenFrontStructureorCantileveredDiaphragm?


OpenFrontStructurewithaCantileveredDiaphragm

AWCSDPWS2015Figure4A

CantileveredDiaphragm SDPWS4.2.5.2

L’/W’≤1.5

WhenTorsionally Irregular

L’/W’≤1,onestory

2/3,multi-story

L’≤35 ft

OpenFrontStructure&CantileveredDiaphragmsinSDPWS2015

Provideddiaphragmsmodelledasrigidorsemi-rigidandfor

seismic,thestorydriftateachedgeofthestructurewithin

allowablestorydriftofASCE7.Storydriftsincludetorsionand

accidentaltorsionalloadsanddeformationsofthediaphragm.

TieDownAttachmenttoConcrete

Source:Strongtie

TieDownBoltwithWasher

Source:Strongtie

TieDownBoltwithWasher- Reinforcing

Source:Strongtie

EmbeddedSteelPlates– WeldonRods

TieDownAnchors– PrecastThroughBolt

TieDownAnchors– ThroughPodium

DiscontinuousShearWalls


Karuna IHolst Architecture

Photo: Terry Malone

OffsetShearWallOverturningResistance

Source:Strongtie

TieDowntoSteelBeamAttachment

Source:Strongtie

TieDowntoSteelBeamAttachment

ShearWalltoPodiumSlabInterface

ASCE7-10Section12.3.3.3andCommentaryC12.3.3.3

providesguidanceonseismicloadrequirementsforvarious

elementssupportingdiscontinuousshearwalls

Recap

• WindLoadPaths

• Multi-StoryStackedShearWallEffects

• AccumulationofOverturningLoads

• ShearWallDeflection

• DiaphragmModeling

• DiscontinuousShearWalls

Questions?

ThisconcludesThe

AmericanInstituteof

ArchitectsContinuing

EducationSystems

Course

RickyMcLain,MS,PE,SE

WoodWorks

[email protected]

(802)498-3310

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

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multi-story lateral design - woodworks · multi-story wind load design diaphragm wind forces do not...

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