Designing Wood Frame Structures For High Winds Wood Frame Structures For High Winds Ricky McLain, MS, PE ... The main changes in wind loads from ASCE 7-05 to ... •ASCE 7-05 § Wind

DesigningWoodFrameStructuresForHighWinds

RickyMcLain,MS,PE,SETechnicalDirector– WoodWorksSEAMASSMeeting10-26-16

Overview

• WindLoadsandCodeChanges• Uplift• WallDesign• Diaphragms• Shearwalls

WindLoads

Windloadsactingonbuildingsaremodeledasuniformsurfaceloads.Windloadscancreatebothpositiveandnegativeloads(inwardsandoutwardsloads)onbuildingsurfacesandcreatethreedifferentloadingconditions:• Uplift• Racking/overturning• Sliding/shear

MassachusettsBuildingCode

Massachusetts8thEditionBuildingCode



IBC2009

ASCE7-05





IBC2015ASCE7-10

MassachusettsAmendments

Massachusetts9th EditionBuildingCode

WindSpeedByLocationSoftware

windspeed.atcouncil.org

WindCodeChanges

ThemainchangesinwindloadsfromASCE7-05toASCE7-10are:

• BasewindloadsareUltimateratherthanASD• Occupancy/ImportancefactorbuiltintoWindSpeedMapsratherthanincludedinequations

• IntroducedinclusionofExposureDinHurricaneProneRegions

• RevisedtriggersforHurricaneProneRegionsandWindBorneDebrisRegions

CalculatingWindLoads

• ASCE7-05§ Chpt.6:ContainedAllProvisions

• ASCE7-10§ Chpt.26:GeneralRequirements§ Chpt.27:MWFRS– Directional§ Chpt.28:MWFRS– Enveloped§ Chpt.29:OtherStructures§ Chpt.30:Components&Cladding§ Appendices

DetermineBasicWindSpeed,VmphASCE7-05

DetermineBasicWindSpeed,Vmph

PerASCE7-10Fig.26.5-1A

115

DetermineBasicWindSpeed,V

• ASCE7-05§ ASDLoads§ 90mphperfig.6-1

• ASCE7-10 (figuresincorporateimportancefactor)§ UltimateLoads§ 115mphperfigure26.5-1AforRKII

§ 120mphperfigure26.5-1BforRKIII&IV

§ 105mphperfigure26.5-1CforRKI

Note:RK=RiskCategoryImageSource:SKGhosh Associates

BasicWindSpeed:Probabilities

• ASCE7-05§ WindSpeedsbasedon50yearreturnperiod

• ASCE7-10§ RKIbasedon300yearreturnperiod(15%probabilityofexceedancein50Years)

§ RKIIbasedon700yearreturnperiod(7%in50years)§ RKIII&IVbasedon1,700yearreturnperiod(3%in50years)

Note:RK=RiskCategory

ASCE7-05to7-10Comparison

ComparingASCE7-05toASCE7-10:LoadCombinations:

7.0.6D+W(ASCE7-05)7.0.6D+0.6W(ASCE7-10)

3SecondWindSpeed:90mph (ASCE7-05)115mph*√0.6=89mph(ASCE7-10)

Finalloadonbuildingisverysimilarforinlandlocations


Example:Boston BasicWindSpeeds

8th EditionMassCode(ASCE7-05)VASD =105mph

9th EditionMassCode(ASCE7-10)VULT =128mph(RKII)VASD =(128)(√0.6)=99mph


So,windloadsperASCE7-10aresimilartoorslightlylowerthanthoseperASCE7-05?

Yes….andNo

ASCE7-10re-introducedthepossibilityofhavingexposureDinhurricaneproneregions

HurricaneProneRegions

Bostonisbydefinitioninahurricaneproneregion:Hurricaneproneregion:AtlanticOceanandGulfof

MexicocoastswhereRKIIbasicwindspeed>115mph(ASCE7-1026.2)

RunningtheNumbers:VelocityPressure

• qz =0.00256KzKztKdV2

§ qz =velocitypressure(psf)§ Kz – Exposurecoefficient,Table30.3-1(7-05Table6-3)

§ Kzt – Topographicfactor,Figure26.8-1(7-05Figure6-4)

§ Kd – Directionalityfactor,Table26.6-1(7-05Table6-4)

WindLoadsTypes

2TypesofWindLoads•MWFRS– MainWindForceResistingSystem

Anassemblageofstructuralelementsassignedtoprovidesupportandstabilityfortheoverallstructure.Thesystemgenerallyreceiveswindloadingfrommorethanonesurface.Eg.Shearwalls,diaphragms

• C&C– Components&CladdingElementsofthebuildingenvelopethatdonotqualifyaspartoftheMWFRS.Eg.Wallstuds

MWFRSMethodOptions

TwoMethodsofCalculatingMWFRSloads:• Envelope:Pressurecoefficientsrepresent“pseudo”loadingthatenvelopethedesiredmoment,shear...Limitedtolow-rise• Directional:Pressurecoefficientsreflectwindloadingoneachsurfaceasafunctionofwinddirection

MWFRSMethodOptions

Howtodecidewhichmethodtouse:Envelope:ASCE7-10Chapter28• Part1:Canbeusedforallregular-shapedenclosed&partiallyenclosedbuildingswithmeanroofheight≤60ft• Part2(Simplified):Canbeusedforallregular-shaped,enclosed,simplediaphragmbuildingswithmeanroofheight≤60ft

MWFRSMethodOptions

Howtodecidewhichmethodtouse:Directional:ASCE7-10Chapter27• Part1:Canbeusedforallregular-shapedbuildings• Part2(Simplified):Canbeusedforallregular-shaped,enclosed,simplediaphragmbuildingswithmeanroofheight≤160ft

MWFRSMethodOptions

ASCE7-10MWFRSOptions

Part1:Enclosed,PartiallyEnclosed,Open

BuildingsAllHeights

DirectionalMethod,CH27 EnvelopeMethodCH28

Part2:Enclosed,Simple

DiaphragmBuildingswithh≤160ft

Part1:Enclosed&PartiallyEnclosedBuildingswithh≤60ft

Part2:Enclosed,Simple

DiaphragmBuildingswithh≤60ft

Note:WindTunnelProcedure(ASCE7-10Chpt 31)canalsobeused

Simplified

,Dire

ctiona

l

Simplified

,Envelop

e

Example:FlatRoof,30’x60’Building:

Ch.27Directional

• WindwardWall(0.8)• LeewardWalls(-0.3)• DetermineGustEffect(G)=0.85• ForMWFRSGCpf =(1.1)(0.85)=0.935

Ch.28Enveloped

§ LimitedtoLow-Rise(h≤60’)§ WindwardWall(0.4)§ LeewardWall(-0.29)§ ForMWFRSGCpf =0.69

35%differenceinloadingnotaccountingforendzones.

ComparisonofmethodstocalculateMWFRS(GCpf)

ASCE7-10Figure28.4-1


MWFRSMethodOptions

Beneficialtousetheenvelopemethodwhenitslimitationsaremet

ASCE7-10Fig.C28.4-1

MinimumWindLoads

ForboththeDirectional&EnvelopeMethods,considerminimumwindloads:ASCE7-10Sections27.1.5&28.4.4:WindLoadsforMWFRSinanenclosedorpartiallyenclosedbuildingshallnotbelessthan:§ 16psf (ultimateor~10psf ASD)forwalls§ 8psf (ultimateor~5psf ASD)forroofsWallandroofloadsshallbeappliedsimultaneously.Thedesignwindforceforopenbuildingsshallbenotlessthan16psf ultimate(openbuildingprovisionsapplyonlytoDirectionalMethod).

BuildingEnclosure

Accountsfordegreetowhichwindforcescanenterandexitastructure,creatingvaryingamountsofinternalwindpressure3buildingenclosureclassifications:

Open,PartiallyEnclosed,andEnclosed

InternalPressureCoefficient– Table26.11-1

+/- 0.18- Enclosed+/- 0.55– PartiallyEnclosed

RunningtheNumbers:DesignWindPressure

• p=qh[(GCp)– (GCpi)]§ p=Designwindpressure(psf)§ qh=velocitypressure(psf)§ GCp:Externalpressurecoefficient

Figures27.4-1,28.4-1,30.4-1Note:Figure27.4-1alsorequiresGusteffectfactor(G)per

section26.9

§ GCpi:Internalpressurecoefficient,Table26.11-1(7-05Figure6-5)

DesignWindPressureTables

ASCE7-10

IBC’sAlternateAll-HeightsMethod

IBCSection1609.6providesanalternativetotheDirectionalWindLoadProcedureinASCE7

AlternateAll-HeightsMethod

Limitationssuchas:• BuildingHeight≤75ft• BuildingHeight/Width≤4• Buildinghassimplediaphragm• Others(IBC1609.6.1)

Pnet =0.00256V2KzCnetKzt


Pnet =0.00256V2KzCnetKzt

• V=Basicwindspeed(ASCE7)• Kz =Exposurecoefficient(ASCE7)• Kzt =Topographicfactor(ASCE7)• Cnet =Net-pressurecoefficient(IBCTable1609.6.2)


IBCTable1609.6.2

WindBorneDebrisRegions

PerASCE7-10,section26.2,WindBorneDebrisregionsareAreaswithinhurricane-proneregionswhereimpactprotectionisrequiredforglazedopenings(buildingsinRiskCategoryIareexempt– ASCE26.10.3&IBC1609.1.2)Protectionofglazedopeningsisrequired(ASCE726.10.3):• Within1mileofthecoastalmeanhighwaterlinewhere

thebasicwindspeedisequaltoorgreaterthan130mph,or

• Inareaswherethebasicwindspeedisequaltoorgreaterthan140mph

• Otherexemptions,testingrequirementsgiveninASCE7-10,section26.10.3

WindBorneDebrisRegions

Image:greenheck.com

Failedopeningscanchangeastructurefromenclosedtopartiallyenclosed,significantlyincreasingwindforces

Overview

• CalculatingWindLoads• Uplift• WallDesign• Diaphragms• Shearwalls

UpliftWindLoads

Uplift– Outward(suction)forceactingonroof

Loadpath- rooftofoundationrequiredunlessdeadloadisgreaterthanuplift

UpliftLoads

Source:strongtie.com

MethodstoResistUpliftLoads

• Mechanicalconnectors(straps,hurricaneties,screws,threadedrods)• Sheathing• DeadLoads

Source:strongtie.com

UpliftResistance:MechanicalConnectors

Source:IIBHS

UpliftResistance:WallSheathing

• Whenjoints,fastenersareconsidered,canusesheathingtoresistuplift

• SDPWSSection4.4

SDPWSFigure4I

UpliftResistance:WallSheathing

SDPWSFigure4J

UsingDeadLoadtoResistUplift

Source:Strongtie

Deadloadfromabove(Wall,Floor,Roof)canbeusedtoresistsomeorallupliftforces,dependingonmagnitude

LoadCombinationsofASCE7-10:06.D+0.6W

UpliftWindLoads

Truss/RaftertoTopPlateConnection

Whathappenstotheupliftloadafterthis?

Uplift:MWFRSorC&C?

ConsidermemberpartofMWFRSif:• TributaryArea>700ft2 perASCE7-1030.2.3• LoadcomingfrommorethanonesurfaceperASCE7-1026.2

Uplift:MWFRSorC&C?

AWC’sWFCMcommentaryC1.1.2statesthatMWFRSisusedforallupliftconditions:

Therationale forusingMWFRSloadsforcomputingtheupliftofroofassembliesrecognizesthatthespatialandtemporalpressurefluctuationsthatcausethehighercoefficientsforcomponentsandcladdingareeffectivelyaveragedbywindeffectsondifferentroofsurfaces.

Uplift:MWFRSorC&C?

ASCE7-1026.2commentaryprovidessomediscussiononuplift&MWFRSvs.C&C.

ComponentsreceivewindloadsdirectlyorfromcladdingandtransfertheloadtotheMWFRS.Examplesofcomponentsincludefasteners,purlins,girts,studs,roofdecking,androoftrusses.ComponentscanbepartoftheMWFRSwhentheyactasshearwallsorroofdiaphragms,buttheymayalsobeloadedasindividual components.

EffectiveWindArea

Forwinddesign,tributaryareadoesnotnecessarily=effectivewindarea

EffectiveWindArea(EWA)- Twocases:• Areaofbuildingsurfacecontributingtoforcebeing

considered(tributaryarea)• Longandnarrowarea(wallstuds,rooftrusses):width

ofeffectiveareamaybetakenas1/3length;increaseseffectivearea,decreasesload(perASCE7-10section26.2commentary);EWA=L2/3

EffectiveWindAreaExample

44’-0”

Trusses@2’o.c.

44’-0”

Trusses@2’o.c.

Trib.A=(44)(2)=88ft2 EWA=442/3=645ft2

UpliftExampleCalculation

• RoofFramingRafter• 20’Span• 2’Spacing• 2’Overhang• 115mphExposureB• RoofH=80ft• 65’x220’

Photocredit:MattTodd&PBArchitects

MWFRS- ExternalPressureCoefficient

Lookatwindactingonbuilding’slongside:L=65ft,h/L=80/65=1.23Cp =-1.3,-0.18

ASCE7-10Fig.27.4-1

• GCp:(0.85)(-1.3)=1.105(26.9.4&Fig.27.4-1)• GCpi:±0.18(Table26.11-1)• qh =0.00256KzKztKdV2

§ Kz :0.93– Table27.3-1§ Kzt :1.00- Figure26.8-1§ Kd :0.85- Table26.6-1§ Vu:115mph

• qh =26.8psf• p=(26.8psf)(-1.105+(-0.18)) =34.4psf

MWFRS- Runningthenumbers

MWFRS- RoofOverhangpersection27.4.4• ForOverhangs:ASCE727.4.4– useCp =0.8onundersideofoverhang,usesametoppressurescalculatedfortyp.roof• poh =(26.8psf)(-0.8)(0.85)=18.2psf• pext =(26.8psf)(-1.105)=29.6psf• poh net=18.2+29.6=47.8psf

Poh

pext

PerASCE7-10section27.4.4

pint

MWRFS- DeterminingtheUpliftLoad• p=(34.4psf)(2ft)=68.8plf• poh =(47.8psf)(2ft)=95.6plf

68.8plf

Uplift=0.6(95.6plf(2ft.)+68.8plf*20ft/2)=528lbsDeadLoad=0.6((2+20/2)*10psf*2ft)=144lbsNetUpliftatLeftSupport=528lbs -144lbs =384lbsNote:Itiscommonpracticetouse2setsofdeadloads:highestpotentialdeadloadsforgravity,lowestpotentialdeadloadsforuplift

95.6plf

C&C- ExternalPressureCoefficient3zoneswithdifferingwindloads:

1:Field2:Perimeter3:Salientcorners

a=smallerof10%ofleasthorizontaldimensionor0.4h,butnotlessthaneither4%ofleasthorizontaldimensionof3ft

ASCE7-10Fig.30.4-2A

C&C- ExternalPressureCoefficient– Fig.30.4-2A

EWA=H2/3=222/3=161ft2

GCP =-1.1FORINTERIOR

ASCE7-10Fig.30.4-2A

• GCp:-1.1(Figure30.4-2A)• GCpi:±0.18(Table26.11-1)• qh =0.00256KzKztKdV2

§ Kz :0.93- Table30.3-1§ Kzt :1.00- Figure26.8-1§ Kd :0.85- Table26.6-1§ Vu:115mph

• qh =26.8psf• p=(26.8psf)(-1.1+(-0.18))=34.3psf

C&C- Runningthenumbers– Zone2

C&C- RoofOverhangpersection30.10• ForOverhangsFigures30.4-2A&30.10-1areutilized• poh =26.8psf(1.7+0.18)=50.4psf• ps =pw =34.3psf• poh net=50.4+34.3=84.7psf

ps

pW

pOH

EWA=2*2=4sfGCp =-1.7

PerASCE7-10Fig.30.10-1 ASCE7-10Fig.30.4-2A

C&C- DeterminingtheUpliftLoad• p=(34.3psf)(2ft)=68.6plf• poh =(84.7psf)(2ft)=169.4plf

68.6plf

Uplift=0.6(169.4plf(2ft.)+68.6plf*20ft/2)=615lbsDeadLoad=0.6((2+20/2)*10psf*2ft)=144lbsNetUpliftatLeftSupport=615lbs -144lbs =471lbsNote:Itiscommonpracticetouse2setsofdeadloads:highestpotentialdeadloadsforgravity,lowestpotentialdeadloadsforuplift

169.4plf

DeterminingtheUpliftLoad

384lbs MWFRSOR471lbs C&[email protected]

RoofFraming:CompressionEdgeBracing

• Bendingcausescompressioninoneedgeofmember• Roofsheathingbracescompressionflangeofroofjoists

Compressionedge

Tensionedge

Loadingdirection

RoofFraming:CompressionEdgeBracing

• WhataboutUplift?Needfulldepthblocking/bridgingorbottomchordbracing

BottomChordBracing

Overview


WindLoads

Uniformsurfacewindloadsgenerallyincreasewithbuildingheight

ASCE7-10Fig.27-6.1

Ifwindloadsvarywithbuildingheight,commontousehigherwindloadoverasinglestoryorbuilding

PanelsL/dRatioUnbraced LengthWallVeneerWindonlyloadingC&CDesignPropertiesHinges

WallDesignConsiderations

WoodFrameDesign

IBC:ReferencesNationalDesignSpecification(NDS)

fordesignofwoodconstruction

NationalDesignSpecification(NDS):Providesdesignproceduresandreferencedesignvaluesusedinthestructuraldesignofwoodframing

membersandconnections

LoadsintoWSP

Windloadsaretransferredtowallframingstudsthroughwoodstructuralpanels(sheathing)

SDPWSTable3.2.1

ForASDCapacity:DivideNominalCapacityby1.6ForLRFDCapacity:MultiplyNominalCapacityby0.85

CalculatingDeflection– IBCTable1604.3

ForΔ ofmostbrittlefinishesusel/240

ForC&Cpressuresa30%loadreductionisallowedforΔ only(IBCTable1604.3footnotef)

f.Thewindloadispermittedtobetakenas0.42timesthe"componentandcladding”loadsforthepurpose ofdetermining deflectionlimitsherein.

WoodStudswithBrickVeneer- Deflection

IBCTable1604.3:min.walldeflectionwithbrittlefinishes=L/240

BrickIndustryAssociationrecommendsmuchstricterlimits

StructureMagazineMay2008article,HaroldSprague

BIATechNote28

WallDesign:MWFRSorC&C?

3StepProcess:ExteriorWallDesign

• StrengthCheck1:Gravity(axial)+MainWindForceLoads

• StrengthCheck2:FullComponentsandCladdingWindLoads,NoAxial(orminimalaxial)

• DeflectionCheck:ReducedComponentsandCladdingWindLoads

WallDesignConsiderations

Forotherdesignissuesseethearticle:

• ConsiderationsinWindDesignofWoodStructures• FreedownloadfromAWCavailableat:

http://www.awc.org/pdf/codes-standards/publications/archives/AWC-Considerations-0310.pdf

StrengthCheck2forStudDesign

StrengthCheckforComponents&CladdingWinds• Noaxialloading• C&CtransverseWindloadsonly• Checkstudbendingandshear.

DesignTip:Forbendingstresscheck,beawareofRepetitiveUsefactorCr ofNDSandWallStudRepetitiveMemberFactorofSDPWS3.1.1.

ChangeinSDPWS2015allowsapplicationofWallStudRepetitiveFactortoStudSTIFFNESS.SeeSDPWS3.1.1

DeflectionCheckforStudDesignDeflectionCheckforComponentsandCladdingWinds• Checkout-of-planedeflectiontoIBCTable1604.3or

othermorestringentrequirements.

Note:Thischeckoftengovernstallwalls

DesignTip:Readallthefootnotes!IBCTable1604.3footnotefallowsthefollowingC&CWindloadreduction:

MultiplycalculatedC&CWindLoadsby0.42whenusingVULT (ASCE7-10)OR0.70whenusingVASD (ASCE7-05andearlier)fordeflection

WallStudDesignAidWesternWoodProductsAssociation(WWPA)DesignSuite:http://www.wwpa.org/TECHGUIDE/DesignSoftware/tabid/859/Default.aspx

Example:OfficeBuildingWallStuds

2StoryBuilding

13’tallwoodframedwalls.

Assumestuds16”o.c.

110mphExposureC

LeastHorizontalDim.=90ft

WallStudDesign:StrengthCheck1

GravityLoads:

RoofDeadLoad=20psf; FloorDeadLoad=30psf

RoofLiveLoad=20psf; FloorLiveLoad=65psf

WallDeadLoad=18psf; WallDeflection=L/360

Roof&FloorTributaryWidth=(22ft)(0.5)=11ft

WallTributaryWidth=13ft +13ft =26ft

WDL =(11ft)(20psf+30psf)+(26ft)(18psf)=1018plf

WRL =(11ft)(20psf)=220plf

WLL =(11ft)(65psf)=715plf

ControllingLoadCombo:D+L=1018+715=1733plf


GravityLoads:

AxialLoadPerStud=(1733plf)(1.333ft)=2310lb

Bottomplatecrushing:2310/(1.5”*5.5”)=280psi<625psi:OK

MWFRSWindLoads:

ULT.=28.5psf;ASD=(28.5psf)(0.6)=17.1psf ASCETable27.6-1


2x6DF#2Studs@16”o.c.OKforStrengthCheck1

Member #

Location :

Sits on Sill Plate ? Yes

** Dimension Lumber ** ** Dimension Lumber **

Yes Nominal Size : ( 1 ) 2 x 6 Sill Plate Nominal Size : 2 x 6

DochDN.2 Species = Species or Symbol = DochDN.2

No.226 Grade = Grade = No.226

2400f-2.0E 1500f-1.4E

Bearing at < 3" of Sill End? No

Height ( H ) = 13 ft - 0 in P = 2310 lb =

Unbraced Length ( l 1 ) = 13 ft - 0 in w = 22.8 plf = Wind

Unbraced Length ( l 2 ) = 2 ft - 0 in lu = 13 ft - 0 in 13

(pressed-down buttons are selected)

Yes Repetitive Use ?

No 1.00 Incised for PT ?

No Flat Use :

< 19% 1.60 Moisture Content : for P only, fc (psi) = 280 < 533 = Fc //

< 100 Temperature (° F) : for P + w, fc (psi) = 280 < 558 = Fc //

1.00 C D = 1.00 (P) & 1.60 (P+w) (1.3/2) fb (psi) = 497 < 1346 = Fb

1.60 K = 1.00 (fc / F'c)2 + fb / [F'b (1 - fc / Fce)] = 0.95 < 1.00 OK

∆ / H = 120 Mid-H Deflection due to w, ∆ (inch) = 0.85 < H / 120 OK

Section Properties

Post/Stud Sill PL

breadth (b) = 1.5 in 1.5 Sill PL

depth (d) = 5.5 in 5.5 Bending Comp // E Comp -|

Area (A) = 8.3 in^2 8.3 Wet Service CM = 1.00 1.00 1.00 1.00

Section Modulus (S) = 7.6 in^3 Temperature Ct = 1.00 1.00 1.00 1.00

Moment of Inertial (I) = 20.8 in^4 Beam Stability CL = 1.00 N/A N/A N/A

Size CF = 1.30 1.10 N/A N/A

Flat Use Cfu = 1.00 N/A N/A N/A

Sill PL Incising Ci = 1.00 1.00 1.00 1.00

Fb Fc // E Fc -| Emin Repetitive Member Cr = 1.15 N/A N/A N/A

Reference 900 1350 1600000 625 580000 Column Stability (P) CP = N/A 0.36 N/A N/A

Adjusted (P) 533 1600000 781 580000 Column Stability (P+w) CPw = N/A 0.23 N/A N/A

Adjusted (P+w) 1346 558 1600000 781 580000 Bearing Area Cb = N/A N/A N/A 1.25

1485

2152.8 2376

Adjustment Factors

How to

Enter Data

Designed on: April 12, 2016

DL + FL

Douglas Fir-Larch

No.2

Design Values (psi)

Douglas Fir-Larch

No.2

Studs

Strength Check 1

PrintOrder Pro VersionDeveloped by:

Forum Engineers

P

H

w

Setup

ASD Method

YesNo

YesNo

<19% >19%

<100 100~125 125~150

YesNo

No Yes

Set Duration Factors

Set Ef f ectiv e-Length Factor

Version: 3.1

Set Def lection Limit


C&CWindLoads:ASCE7Fig.30.4-1

a=Lesserof:

• 10%leasthorizontaldimension(LHD)90’*0.1=9’• 0.4h=0.4*26=10.4’.

Butnotlessthan:

• 0.04LHD=3.6’or3’

Usea=9’forzone5

StrengthCheck2:C&CWindLoads

Wallstudsare13’longEWA=h2/3=56ft2

Zone4:GCpf =-0.97GCpi =-0.18(Table26.11-1)Zone5:GCpf=-1.1


Runningthenumbers– Zone4

• GCpf:0.97(Figure30.4-1)• GCpi:0.18(Table26.11-1)• qh =0.00256KzKztKdV2

§ Kh :0.98- Table30.3-1§ Kzt :1.00- Figure26.8-1§ Kd :0.85- Table26.6-1§ V:110mph

• qh =25.8psf• p=25.8psf(0.97+0.18)=29.7psf• 0.6W=0.6(29.7)=17.8psf

StrengthCheck2&DeflectionCheck(Zone4)

2x6DF#2Studs@16”o.c.OKforStrengthCheck2&DeflectionCheck

Member #

Location :






2400f-2.0E 1500f-1.4E


Height ( H ) = 13 ft - 0 in P = 1357 lb =






No Flat Use :



1.00 C D = 1.00 (P) & 1.60 (P+w) (1.3/2) fb (psi) = 516 < 1346 = Fb



Section Properties

Post/Stud Sill PL






Size CF = 1.30 1.10 N/A N/A







1485

2152.8 2376

Adjustment Factors

How to

Enter Data


DL + FL

Douglas Fir-Larch

No.2

Design Values (psi)

Douglas Fir-Larch

No.2

Studs

Strength Check 1


Forum Engineers

P

H

w

Setup

ASD Method

YesNo

YesNo

<19% >19%

<100 100~125 125~150

YesNo

No Yes



Version: 3.1


• GCp:1.1(Figure30.4-1)• GCpi:0.18(Table26.11-1)• qh =0.00256KzKztKdV2

§ Kh :0.98- Table30.3-1§ Kzt :1.00- Figure26.8-1§ Kd :0.85- Table26.6-1§ V:110mph

• qh =25.8psf• p=25.8psf(1.1+0.18)=33psf• 0.6W=0.6(33)=19.8psf

Runningthenumbers– Zone5

StrengthCheck2&DeflectionCheck(Zone5)

2x6DF#2Studs@16”o.c.OKforStrengthCheck2&DeflectionCheck

Member #

Location :






2400f-2.0E 1500f-1.4E


Height ( H ) = 13 ft - 0 in P = 1357 lb =






No Flat Use :



1.00 C D = 1.00 (P) & 1.60 (P+w) (1.3/2) fb (psi) = 575 < 1346 = Fb



Section Properties

Post/Stud Sill PL






Size CF = 1.30 1.10 N/A N/A







1485

2152.8 2376

Adjustment Factors

How to

Enter Data


DL + FL

Douglas Fir-Larch

No.2

Design Values (psi)

Douglas Fir-Larch

No.2

Studs

Strength Check 1


Forum Engineers

P

H

w

Setup

ASD Method

YesNo

YesNo

<19% >19%

<100 100~125 125~150

YesNo

No Yes



Version: 3.1


GableEndWallHinge

GableEndBracingDetails

• Gableendwallandroofframingmayrequirecrossbracing

FullHeightStudsatGableEndWalls

• Ifnoopeningsingableendwallexist,candesignstudstospanfromfloor/foundationtoroof(varyingstudheights).Mayrequirecloserstudspacings attallerportionsofwall

GableEndWallswithOpenings

GableEndWallswithOpenings

GableEndWallGirts&Jambs

• Oftengableendwallsarelocationsoflargewindows• Horizontally spanningmemberinplaneofwallbreaksstudlength,providesallowable

opening

Verticallyspanningjambs

Horizontallyspanning

girts

DroppedHeaders:OutofPlaneBraced?

OutofPlaneBracing

SmallRetailBuilding– NorthernCA

SmallRetailBuilding– NorthernCA

WoodFramedStair/ElevatorShaftWalls

WoodFramedStair/ElevatorShaftWalls

StairwayShaftEnclosures&Framing

IntermediateStairLanding

WhenStairShaftWallisExteriorWall

WallPlatesatTypicalFloorElevation– CreatesPotential“Hinge”

WallFramingatShafts


Framing

Shaftwall

StairExteriorWallDetail

StairShaftSide

ExteriorSide

Consider“Hinge”atwallplatesforout-of-planewind&seismicloadsduetolackofadjacentfloor:• Installadditional

member(rim)tospanhorizontally

• Optionsincludesolidsawnlumber(4xor6x),glulam,PSL

• Ifmulti-plymember,uniquedesignconsiderations




ExteriorWallPlateElevationsShiftedDowntoIntermediate

LandingElevation

• EliminatesHingeEffect• AvoidsInterferencewith

LandingWindows

WhenStairShaftWallisExteriorWall

Overview


DiaphragmDesign

WindLoadDistributiontoDiaphragm

WINDINTODIAPHRAGMS

WINDSURFACELOADSONWALLS

WindLoadPaths

WINDINTODIAPHRAGMSASUNIFORMLINEARLOADS

WindLoadPaths

DIAPHRAGMSSPANBETWEEN

SHEARWALLS

WINDINTOSHEARWALLSASCONCENTRATEDLOADS

StudtoDiaphragm

WINDLOAD

DIAPHRAGMSHEATHING

Floor/Roofframingperpendiculartowalls

FLOORJOIST

StudtoDiaphragm

WINDLOAD

DIAPHRAGMSHEATHING

Floor/Roofframingparalleltowalls(addblocking)

FLOORJOIST

BLOCKING

UnblockedDiaphragm

BlockedDiaphragm

WoodFrameLateralDesign

IBC:ReferencesSpecialDesignProvisionsforWind&Seismic(SDPWS)forcapacitiesofmost woodframed

lateralsystems.IBCprovidescapacityofstapledWSPandgypsumshearwalls

SDPWS:Providescapacitiesofmostwood-framedverticalandhorizontallateralforceresisting

systems

AssumeBasicWindSpeed=115mphUltimate

ExposureB

DiaphragmDesign

• Capacity

Shearwall Design• Conventional• ForceTransferAroundOpening• PerforatedShearwall

Example:RetailRestaurant

RetailRestaurant– DiaphragmDesign

CriticalShearwall atfrontofbuildingCheckDiaphragmforwindloadson84’wall

84’

34’

10’6’ 8’5’

6’

6’

6’6’

6’

3’3’

4’

29’24’

DiaphragmAspectRatios

SDPWSTABLE4.2.4TYPE- MAXIMUMLENGTH/WIDTHRATIO

Foran84x34diaphragmtheaspectratiois2.5<3.DiaphragmaspectratioisOK.

Woodstructural panel,unblocked 3:1Woodstructural panel,blocked 4:1Single-layerstraightlumbersheathing 2:1Single-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


ParapetDesign– Figure27.6-2

Atparapetswindwardandleewardpressuresoccuroneachparapet.

Section27.4.5:Pp =q(GCpn)GCpn =1.5Windwardparapet,-1.0LeewardparapetWindwardParapetGCpf is1.5:16.4*1.5*0.6=14.76psfLeewardParapetGCpf is1.0:16.4*1.0*0.6=9.84psfNetParapet=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’

P=(9.6psf*(5’+3’)+(24.6)*3’)*(84’/2)=6,325lb

νdiaphragm =6,325lb/34’νdiaphragm =186plf

P

DiaphragmTypes

CASE1DIAPHRAGM•HigherShearValues•Panelsperpendiculartofloorframingforimprovedperformance

CASES2-6Maybepreferredforlowsheardemandwherechangingframingdirectionhelps•HVACruns•FireBlocking/DraftStopping

RoofTrusses4x8sheathingN-S

DiaphragmTypes

SDPWSTables4.2A&B

DiaphragmCapacity- SDPWSChpt 4

• CapacitiesareNominal:ModifybyASDreductionfactorof2,ModifybyLRFDmultiplicationfactorof0.8

• CapacityisreducedforspecieswithSpecificGravity<0.5• ForSprucePineFirmultiplyby0.92

DiaphragmCapacity:SDPWSTable4.2C

PANELGRADE

COMMONNAILSIZEORSTAPLEfLENGTHANDGAGE

MINIMUMFASTENERPENETRATIONINFRAMING

MINIMUMPANELTHIICKNESS

MINIMUMNOMINALWIDTHOFFRAMINGMEMBERSATADJOININGPANELEDGESANDBOUNDARIESg

NAILSPACINGATALLPANELEDGES

Case1(Nounblockededgesorcontinuousjointsparalleltoload)

Allotherconfigurations(Cases2,3,4,5and6)

Sheathing&singlefloor

8d(2½“x0.131”)

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

Multi-StoryWindDesign

FloorPlanSource:WoodWorks Five-StoryWood-FrameStructureoverPodiumSlabDesignExample

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.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-planedeflectionofthediaphragmunderlateralloadismore

thantwotimestheaveragestorydriftofadjoiningverticalelementsoftheseismicforce-resistingsystemoftheassociatedstoryunderequivalenttributarylateralloadasshowninFig.12.3-1.

IBC2012Chapter2Definition(Wind&Seismic)

Adiaphragmisrigid forthepurposeofdistributionofstoryshearandtorsionalmomentwhenthelateraldeformationofthe

diaphragmislessthanorequaltotwotimestheaveragestory

drift.

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

RobustAspectRatiobutonlysupportedon

3sides…

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.

SmallOpeningsinDiaphragms

http://cwc.ca/wp-content/uploads/2013/11/Design-example-of-designing-for-openings-in-wood-diaphragm.pdf

Accountingforopeningsinshearpanels(diaphragmsandshearwalls)isacoderequirement(IBC2305.1.1)

Nocodepathforcheckingminimumsizeopeninglimit(otherthanprescriptivedesign– IBC2308.4.4.1&2308.7.6.1)

Doyouneedtoaccountfora12”squareopeninginadiaphragm?

SmallOpeningsinDiaphragms

FPInnovationsmethodforcheckingsmallholesindiaphragms:

Recommendrunningananalysisoftheopening’seffectsonthediaphragmunlessthefollowingconditionsaremet.

Overview


WindLoadscreateshear(sliding)andrackingforcesonastructure

Slidingresistedbyshearwall baseanchorageRackingresistedbyshearpanel&fasteners

Shearwall Functions

ShearWallComponents:WallFraming

Strut/collector

WallFraming(Studs)

BlockingBetweenStudsatAllPanelEdges

WallTopPlates

WallSolePlate

Note:Canuse“un-blocked”wallbutcapacitiescanbesignificantlylower:SDPWS4.3.3

ShearWallComponents:WSP&Fasteners

Strut/collector

FieldorIntermediateNailing– Typ.12”o.c.

BoundaryNailing–Typ.2”– 6”o.c.

BoundaryNailing:Attachesall4edgesofeverypaneltowallframing(studs,blocking,top&soleplates)

FieldorIntermediateNailing:Attachespaneltointermediatewallframing(studs)notalongpaneledges

SheathingPanelsOSBorPlywood

PanelFasteners

Duetocantilevernatureofshearwalls,overturningforcesarealsogenerated

Overturningforcesareresistedbytension/compressioncouple–tensionportionresistedbydeadloadsandholddownanchors

Shearwalls - Overturning

Shearwall - CantileverMember

Tensionedge

Compressionedge

ShearWallComponents:BaseAnchorage,EndPosts&HoldDowns

Strut/collector

SolePlateUniformAnchorage:Transfersshearfromwallsoleplatetofloor/wallorfoundationbelow.

SolePlateUniformAnchorage(Nails,Screws,Anchor

Bolts)

WallEndPost&HoldDown:Transfersverticaltension&compressionforcestofloor/wallorfoundationbelow.

WallEndPost&HoldDown

WallEndPosts(SizedforTension&Compression)

ShearWallHoldown Options

StandardHoldownInstallationStrapHoldown

Installation

…………

………

Continuous RodTiedown Systems

6+kipstorytostorycapacities

13+kipcapacities

100+kipcapacities20+kips/level

ThreadedRodTieDownw/TakeUpDevice

Source:Strongtie Source:hardyframe.com

ThreadedRodTieDownw/oTakeUpDevice

Shearwall AspectRatio

NDSSDPWSTABLE4.3.4

MAXIMUMSHEARWALLDIMENSIONRATIOS

1.ForWSPshear walls with AR>2:1,multiply shear wall capacity by1.25- 0.125h/bs

Woodstructural panels,blocked 3½:11

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.Canalso

usehorizontalanddiagonalboardsheathing,gypsumpanels,fiberboard,lathandplaster,andothers

• Blockedshearwallsmostcommon.SDPWShasreductionfactorsforunblockedshearwalls

• Capacitiesaregivenasnominal:mustbeadjustedbyareductionorresistancefactortodetermineallowableunitshearcapacity(ASD)orfactoredunitshearresistance(LRFD)

Shearwall Capacity- SDPWSChpt 4

Shearwall Capacity- SDPWSChpt 4

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


CalculatingMWFRSWindLoads


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

Atparapetswindwardandleewardpressuresoccuroneachparapet.

Section28.4.2:Pp =q(GCpn)GCpn =1.5Windwardparapet,-1.0LeewardparapetWindwardParapetGCpf is1.5:20.14*1.5*0.6=18.12psfLeewardParapetGCpf is1.0:20.14*1.0*0.6=12.08psfNetParapet=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)

Directionalvs.Envelope

Onespecificinstancewhenenvelopeloadscanbehigher

thandirectional:VelocityExposureCoefficient,Kh

BuildingH<30ft,ExposureB

Envelope– Table28.3-1

Directional– Table27.3-1

Questions?

ThisconcludesTheAmericanInstituteofArchitectsContinuingEducationSystemsCourse RickyMcLain,MS,PE,SE

TechnicalDirector- [email protected](802)498-3310

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

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