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Lateral Design of Mid- Rise Wood Structures for Wind Loads Presented by Ricky McLain, MS, PE, SE Houston Wood Solutions Fair September 14, 2016
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
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
SHEARWALLWINDFORCESDOACCUMULATE-UPPERLEVELFORCESADDTOLOWERLEVELFORCES
PublishedMulti-StoryShearWallDesignExamples
Freedownloadatwoodworks.org
SEAOCStructural/SeismicDesignManualVolume2PublishedbyICC
Multi-StoryWindDesign
ElevationSource:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample
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
Collector&DragDesign
ShearWallConstruction
ShearTransferDetailing
ShearResistance
ComponentsofShearWallDesign
Typ.ShearWallElevationWindForcesPerStory29’-0”
10’-0”Typ.
F5 =5.2k
F4 =3.8k
F3 =3.7k
F2 =3.6k
F1 =3.4k
FP =1.7k
ComponentsofShearWallDesign
Typ.ShearWallElevationAccumulatedWindForces29’-0”
10’-0”Typ.
F =5.2k
F=9k
F=12.7k
F=16.3k
F=19.7k
F=21.4k
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
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
ComponentsofShearWallDesign
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
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 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
Possible Shear Wall Layouts
Typical Unit
7654321
D
C
B
A
TheCantileverDiaphragmOption
Possible Shear Wall Layouts
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
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.
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:
WindLoadDistributiontoShearwalls
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
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