designing wood frame structures for high winds · per asce 7-10, section 26.2, wind borne debris...
TRANSCRIPT
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
MassachusettsBuildingCode
Massachusetts8thEditionBuildingCode
IBC2009
ASCE7-05
MassachusettsBuildingCode
Massachusetts9thEditionBuildingCode
MassachusettsBuildingCode
Massachusetts9thEditionBuildingCode
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
ASCE7-05to7-10Comparison
Example:Boston BasicWindSpeeds
8th EditionMassCode(ASCE7-05)VASD =105mph
9th EditionMassCode(ASCE7-10)VULT =128mph(RKII)VASD =(128)(√0.6)=99mph
ASCE7-05to7-10Comparison
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
ASCE7-10Figure27.4-1
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
IBC’sAlternateAll-HeightsMethod
Pnet =0.00256V2KzCnetKzt
• V=Basicwindspeed(ASCE7)• Kz =Exposurecoefficient(ASCE7)• Kzt =Topographicfactor(ASCE7)• Cnet =Net-pressurecoefficient(IBCTable1609.6.2)
IBC’sAlternateAll-HeightsMethod
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
• CalculatingWindLoads• Uplift• WallDesign• Diaphragms• Shearwalls
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
WallStudDesign:StrengthCheck1
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
WallStudDesign:StrengthCheck1
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
WallStudDesign:StrengthCheck2
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
ASCE7-10Figure30.4-1
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 :
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 = 1357 lb =
Unbraced Length ( l 1 ) = 13 ft - 0 in w = 23.7 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) = 164 < 533 = Fc //
< 100 Temperature (° F) : for P + w, fc (psi) = 164 < 558 = Fc //
1.00 C D = 1.00 (P) & 1.60 (P+w) (1.3/2) fb (psi) = 516 < 1346 = Fb
1.60 K = 1.00 (fc / F'c)2 + fb / [F'b (1 - fc / Fce)] = 0.62 < 1.00 OK
∆ / H = 360 Mid-H Deflection due to w, ∆ (inch) = 0.32 < H / 360 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
• 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 :
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 = 1357 lb =
Unbraced Length ( l 1 ) = 13 ft - 0 in w = 26.4 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) = 164 < 533 = Fc //
< 100 Temperature (° F) : for P + w, fc (psi) = 164 < 558 = Fc //
1.00 C D = 1.00 (P) & 1.60 (P+w) (1.3/2) fb (psi) = 575 < 1346 = Fb
1.60 K = 1.00 (fc / F'c)2 + fb / [F'b (1 - fc / Fce)] = 0.68 < 1.00 OK
∆ / H = 360 Mid-H Deflection due to w, ∆ (inch) = 0.36 < H / 360 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
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
IntermediateStairLanding
Framing
Shaftwall
StairExteriorWallDetail
StairShaftSide
ExteriorSide
Consider“Hinge”atwallplatesforout-of-planewind&seismicloadsduetolackofadjacentfloor:• Installadditional
member(rim)tospanhorizontally
• Optionsincludesolidsawnlumber(4xor6x),glulam,PSL
• Ifmulti-plymember,uniquedesignconsiderations
StairwayShaftEnclosures&Framing
StairwayShaftEnclosures&Framing
IntermediateStairLanding
ExteriorWallPlateElevationsShiftedDowntoIntermediate
LandingElevation
• EliminatesHingeEffect• AvoidsInterferencewith
LandingWindows
WhenStairShaftWallisExteriorWall
Overview
• CalculatingWindLoads• Uplift• WallDesign• Diaphragms• Shearwalls
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
ASCE7-10Figure27.4-1
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
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-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
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.
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
• CalculatingWindLoads• Uplift• WallDesign• Diaphragms• Shearwalls
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
ASCE7-10Figure28.4-1
CalculatingMWFRSWindLoads
ASCE7-10Figure28.4-1
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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