Wind Design Consideraxons for Joists and Joist Girders - NET

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Copyright©2017SteelJoistIns;tute.AllRightsReserved.

WindDesignConsidera.onsfor

JoistsandJoistGirdersA P R I L 1 9 , 2 0 1 7

KeithJuedemann,PE–CanamBuildingsTimHoltermann,PE,SE–CanamBuildings

LearningObjec.ves

•  Appropriateloadcombina.onsinvolvingwind.

•  Appropriateloadpathsforwindforces.

•  Detailsforconnec.onsandthetransferofwindforces.

•  Newdevelopmentsaffec.ngwinddesign.

2

Outline

•  Windforcesontheroof

–  Fromthebuildingcode

–  Loadcombina.ons

–  UpliF–  Downwardwind

•  Windeffectsonjoistsystem

–  Endanchorage–  Bridging

3

Outline

•  Lateralwindloads–  Diaphragmsandcollectors

–  Loadpathsandtransferdetails–  Bracingforwindforces

•  Membraneroofs

•  Newcodedevelopments

4

MechanicsofWindForces

5

NatureofWindForces

6

NatureofWindForces

7

8

NatureofWindForces

9

NatureofWindForces

NatureofWindForces

10

WindUpliFonJoistsandDeck•  Evenifthesystemisrobust,ithastostayonthe

building!

11

•  2015SteelJoistIns.tute(SJI)StandardSpecifica.onsandCodeofStandardPrac.ce

•  ProvisionsfromASCE7-10

12

StandardsandCodes

13

History:1965StandardBuildingCode

14

History:1976UniformBuildingCode

•  WindLoads

–  107pagesofcode–  62pagesofcommentary

•  Fromtwohalf-sizepagesto169full-sizepages

•  Over170.mesthelengthof40yearsago

American Society of Civil Engineers

ASCE 7-10 Minimum Design Loads for Buildings and Other Structures

15

•  Itisrela.velysimplewithamonolithicbuildingstructuremadeupoflargerectangularelements.

•  Whenthebuildingshapeismorecomplexandcomprisedofnumerouselements,itisnotaseasytodeterminetheloadingsonjoiststhatpassthroughbothedgeandcornerzones.

16

ASCE7-10WindLoads

ASCE7-10WindLoads

•  Manysteeljoiststructureswillqualifyforthesimplifiedmethodsfordeterminingwindloads.

–  Part2ofChapter28forMWFRS

–  Part2ofChapter30forC&C

•  Condi.onsrequiredforuseofthesimplifiedmethodforC&Cloadsinclude:

–  Roofheightof60feetorless–  Enclosedstructure–  Regular-shapedbuilding–  Roofisnotsteeplysloped

17

ASCE7-10WindLoads

18

19

ASCE7-10WindLoads

ASCE7-10WindLoads

20

21

ASCE7-10WindLoads

DeterminingWindLoadsforJoists

•  SteelJoistIns.tute(SJI)CodeofStandardPrac.ce

22


•  ASCEprovidesformulasfordesignwindpressuresandnetdesignwindpressures.TheseareNOTthesameastheNETupliFrequiredbySJI.

•  ASCEnetisthesumofinternalandexternalpressures.•  SJInet,isthefinalresultantpressure,lessappropriatedeadload–resultoftheloadcombina.on

23

•  2.3COMBININGFACTOREDLOADSUSINGSTRENGTHDESIGN–  2.3.2BasicCombina.ons

1.  1.4D 2.  1.2D + 1.6L + 0.5(Lr or S or R) 3.  1.2D + 1.6(Lr or S or R) + (L or 0.5W) 4.  1.2D + 1.0W + L + 0.5(Lr or S or R) 5.  1.2D + 1.0E + L + 0.2S 6.  0.9D + 1.0W 7.  0.9D + 1.0E

24

ASCE7-10LoadCombina.ons

•  2.4COMBININGNOMINALLOADSALLOWABLESTRESSDESIGN–  2.4.1BasicCombina.ons

1. D 2. D + L 3. D + (Lr or S or R) 4. D + 0.75L + 0.75(Lr or S or R) 5. D + (0.6W or 0.7E) 6a. D + 0.75L + 0.75(0.6W) + 0.75(Lr or S or R) 6b. D + 0.75L + 0.75(0.7E) + 0.75S 7. 0.6D + 0.6W 8. 0.6D + 0.7E 25

ASCE7-10LoadCombina.ons

WindLoadFactorsHaveChanged

•  ASCE7-05(nominalwindmaps)

–  1.0ASD/1.6LRFD

•  ASCE7-10(ul.matewindmaps)

–  0.6ASD/1.0LRFD

26


•  WhenwindupliFisadesignconsidera.on,itshouldbespecifiedasnetupliFonthesteeljoistsandjoistgirders.

•  Thechartonthefollowingslideisatypicalcomponentsandcladdingroofwindpressuresprovidedonthecontractdocuments.

27

ROOF SURFACES

EFFECTIVE WIND AREA

POSITIVE PRESSURES (PSF)

NEGATIVE PRESSURES (PSF)

ZONE

1

2

3

1

2

3

10 SF

12.4

12.4

12.4

-30.4

-51.0

-76.8

20 SF

11.6

11.6

11.6

-29.6

-45.6

-63.6

50 SF

10.6

10.6

10.6

-28.6

-38.4

-46.2

100 SF

9.8

9.8

9.8

-27.8

-33.0

-33.0

28



•  RoofpressureneedstobeconvertedtonetupliF,ormorecorrectly,theresultoftheappropriateloadcombina.onforwindforcesac.ngupward.

•  ThespecifyingprofessionalknowsthedesigndeadloadandiftherearecollateraldeadloadsthatshouldnotbedeductedfromthegrossupliF.

–  MaximumDeadLoad(forgravityloading)

–  MinimumDeadLoad(forwindupliF)

•  DLmin=DLmax-CollateralLoad

29


•  Joistsareconsideredcomponentsandcladding(C&C).

•  PerASCEdefini.onofEffec.veWidth,thewidthneednotbelessthanonethirdthespan.

•  Soforsteeljoists,asimpleruleisthatforalljoistspansof18footorgreater,usethe100squarefootvalues,i.e.18x6=106>100F.2

•  Ifaprojectdoesnothaveanyspanslessthan18feet,thereisnoneedforadetailedchartwithvaluesbysquarefoot.

30


•  Joistgirderscanbeconsideredpartofthemainwindforce-resis.ngsystem(MWFRS).–  Typically,separateMWFRSpressurevaluesarenotprovidedforthejoistgirders,andthejoistdesignerappliestheC&CnetupliFforcesfromthejoiststothejoistgirders.

•  Joistgirdertensionwebsmustbedesignedtoresist,incompression,25percentoftheiraxialforce.

•  UpliFloadsonaJoistGirderoflessthan25percentofthegravityloadshaveminimalornoeffectonthegirderdesign.

31


•  OverhangshavesignificantupliF–  Joisttopchordextensions(TCX)“automa.cally”havesamecapacityasdownwardgravity.

–  UpliFonoverhangscaneasilyexceedgravity,par.cularlyincoastalareasorhurricaneproneregions.

32

Presenta.onofUpliFDesign•  UseaNetUpli)plan

33

Presenta.onofUpliFDesign•  UseaNetUpli)plan

34

•  Let’scompromise

35

Presenta.onofUpliFDesign

Presenta.onofUpliFDesign•  Notenoughdirec.on

36

DesignExample

37

DesignExample

•  RiskcategoryII•  V=115(typicalforinteriorpor.onsofcon.guous

UnitedStates)

•  Kzt=1.0•  CompareexposurecategoriesB&C

•  Rectangularbuildingwithheight=40’,andflatroof•  Simplifiedmethodforcomponents&cladding:

38

DesignExample

•  Joistsplacedat6’-0”oncenterandspanning50’•  DL=15psf&LL=20psf•  UseASD•  Totaluniformgravityload=210plf

•  Uniformliveload=120plf

•  Select30K8(225/130loadingfromSJItables)

•  Joistweightisapproximately460pounds

39

DesignExample

DesignExample

•  ForexposureBand100squarefooteffec.vearea,pnet=1.09x1.0x-21.8=-23.8psf

•  NetupliF=0.6D+0.6W=0.6(15)+0.6(-23.8)=-5.3psf

•  @6’-0”spacing=32plfnetupliFOnly15%ofgravityloadingof210plf

•  Thisloadcasedoesnotaddweightorcosttothejoist.NotethatupliFbridgingisrequired.

41

DesignExample

•  Let’sassumeplansarenotclearandthejoistsupplierusesthepnet=-23.8psfasthenetupliF.

•  @6’-0”spacing=143plfnetupliFNow68%ofgravityloadingof210plf

•  30K8with143plfnetupliFweightsabout610pounds.33%heavierthan30K8suppor.ngrequirednetupliF

42

DesignExample

DesignExample

•  ForexposureCand10squarefooteffec.vearea,pnet=1.49x1.0x-23.8=-35.5psf

•  NetupliF=0.6D+0.6W=0.6(15)+0.6(-35.5)=-12.3psf

•  @6’-0”spacing=74plfnetupliF35%ofgravityloadingof210plf

•  30K8with74plfnetupliFweightsabout490pounds.7%heavierthan30K8suppor.ngrequirednetupliF

44

Posi.veWindPressureConsidera.ons

•  Thetotaljoistloadforthepurposesofselec.ngajoistdesigna.onshouldrepresentthemaximumresultoftheloadcombina.ons,whichmayincludeadownward(posi.ve)windforceinthecontrollingloadcase.–  ForLRFD

•  1.2D+1.6(LrorSorR)+(Lor0.5W)•  1.2D+1.0W+L+0.5(LrorSorR)

–  ForASD•  D+(0.6Wor0.7E)•  D+0.75L+0.75(0.6W)+0.75(LrorSorR)

45

Posi.veWindPressureConsidera.ons

•  Example(ASD)

DeadLoad(D)=15psf

LiveLoad(Lr)=20psf

Posi.veWind(W)=16psf (130mph,60’height,exposureC,100sq.F.eff.area)

TotalDesignLoad=D+Lr=35psf

Or

D+0.75(0.6W)+0.75(Lr)=37.2psfßGoverns

46

Wind–NottobeTakenLightly!

47

ApplyingWindUpliFtoJoists

•  Connec.onsareacri.calpartoftheloadpath –  Designofjoistseat

–  Capacityofatachment

•  Welds

•  Bolts

48

Connec.onDesignforUpliF

•  Anchoragefailureexample

49

Connec.onDesignforUpliF

•  DivisionofResponsibility–  SJISpecifica.onandCodeofStandardPrac.ce

•  “ThejoistmanufacturerwillprovideaseatofsufficientthicknessandstrengthtoresisttheupliFendreac.onresul.ngfromthespecifiedupliF.”

•  “Theadequacyoftheendanchorageconnec.on(boltedorwelded)betweenthejoistorJoistGirderbearingseatandthesuppor.ngstructureistheresponsibilityofthespecifyingprofessional.Thecontractdocumentsshallclearlyillustratetheendanchorageconnec.on.”

50

WeldedEndAnchorage

•  ThestrengthofthejoistbearingseatforanupliFloadingcombina.onisafunc.onofboththejoistseatthicknessandlengthoftheendanchoragewelds.

•  TheminimumanchorageweldsfromtheSJISpecifica.onmaynotdevelopthefullcapacityofthejoistseatassemblyforupliF.

•  Longerendanchorageweldlengthaidsthejoistmanufacturerinprovidinganeconomicaldesignofthejoistbearingseat.

51

Failure Mechanism

52

WeldedSeatTes.ng

Yield Line Perimeter

53

WeldedSeatTes.ng

Anchorage Weld (typ.)

Yield Line Formation (typ.)

Anchorage Weld (typ.)

Yield Line Formation (typ.)

54

WeldedSeatYieldLine

a

Δθ

Plastic Hinge

Pu/2

Pu/2 Yield Line

a

Lw Ls

a

a

55

WeldedSeatYieldLine

Pn=2MpLyl/a

Where: Pn = NominalupliFcapacity

Mp = Plas.cmomentcapacityofplateperunitlength

= FyZ

Z = t2/4

Lyl = Lengthofyieldline

a = 2.3t

Ω = 1.67(AISC-ASDsafetyfactorforbending)

Pn/Ω= AllowableupliFstrength

φ = 0.90(AISC-LRFDresistancefactorforbending)

φPn = DesignupliFstrength

YieldLineDesignProcedure

56

MinimumEndAnchorageWelds

JOIST SERIES and SECTION NUMBER

MINIMUM FILLET WELD

K Series (2) 1/8” x 2-1/2”

LH Series, 02-06 (2) 3/16” x 2-1/2”

LH/DLH Series, 07-17; JG (2) 1/4” x 2-1/2”

DLH Series, 18-25; JG* (2) 1/4” x 4”

*JoistGirderswithaselfweightgreaterthan50plf.

57

BoltedEndAnchorage

•  Finalweldingistypicalforstability(lateralsupport)

•  OnlyboltsareconsideredanchorageforupliF–  Typeanddiameterbyspecifyingprofessional

–  ProvidesufficienttensilestrengthforupliFreac.on

–  HigherstrengththanminimumsperSJImayberequired

58

BoltedEndAnchorage

JOIST SERIES and SECTION NUMBER

MINIMUM BOLTS

K Series (2) 1/2” A307

LH Series, 02-06 (2) 1/2” A307

LH/DLH Series, 07-17; JG (2) 3/4” A307

DLH Series, 18-25; JG* (2) 3/4” A325

*JoistGirderswithaselfweightgreaterthan50plf.

59

BoltedConnec.onDesignforUpliF

•  Thebearingseatdesignisacheckofpryingac.on–  AISCdesignprocedureisfollowed–  AnupliFreac.onequaltothefulltensilecapacityoftheboltsmaynotbeachievedwithmaximumprac.calseatthicknessesandwithouts.ffeners.

60

TypicalPryingAc.onCapacityConnection Type to Supporting Member LRFD Strength Kips ASD Strength Kips

(2) ½” A307 bolts (1/4” steel) 10.5 7.0

(2) ½” A325 bolts (1/4” steel) 10.5 7.0

(2) ¾” A307 bolts (1/2” steel) 26.4 17.6

(2) ¾” A325 bolts (1/2” steel) 36.0 24.0

(2) 1” A325 bolts (1” steel)

106.0 70.7

61

•  Capaci.esonthepriorslidewerebetween51%and100%ofthefulltensileboltstrength,dependingonthethicknessofthebearingseatleg.

•  Aruleofthumbwouldbetosizetheboltdiameter,grade,andquan.tyofboltsbaseduponusing75%ofthefulltensilestrength(allowingtheremainingcapacityforpryingac.on).

62

TypicalPryingAc.onCapacity

Connec.onDesignforUpliF•  Whereajoistseathasbeendetailedforabolted

connec.on,andforanyreasontheboltisnotu.lized,theemptyslotinthebearingseatlegseverelydiminishesupliFcapacity.Insuchacondi.on,ifaweldandnoboltistobeusedonaslotedbearingseat,thentheweldshouldbeappliedwithintheemptyslot.

63

TypicalBoltedJoistConnec.on

64

EndAnchorage

•  FormoreonEndAnchorageandjoistdesignforupliF,refertotheSteelJoistIns.tuteTechnicalDigest#6,DesignofSteelJoistRoofstoResistUpliNLoads

65

BotomChordBridgingforUpliF•  UpliFProducesStressReversal

–  Compressiveaxialloadinbotomchord

•  Requireslateralbracing

•  Onlybridgingisavailable

BotomChordBridgingforUpliF•  SJIStandardSpecifica.onsrequirebridgingatthefirst

botomchordpanelpoint,sincetwoofthethreeintersec.ngprimarymembersareincompressionunderupliFloading.

67

BotomChordBridgingforUpliF

•  SJIStandardSpecifica.ons,UpliFBridging–  Botomchordbridgingneednotalignwithtopchordbridging

–  Totalnumberofbotomchordrowsshallnotbelessthanthenumberoftopchordrows

–  Canbeadvantageoustospacerowsmorecloselynearcenterofspan

–  Commonlyequalspacingonbotomchord

68

BotomChordBridgingSpacing•  Typicaldetailsused–equallyspacebetweenfirstbotom

chordpanelpoints

69


•  BridgingLoadRequirements

–  Bridgingaxialloadisbasedonbotomchordcompressiveaxialload

•  Pbr=0.005Pc•  WherePcisthebotomchordcompressiveaxialload

–  Bridgingdesignforcefornumberofjoists,n,doesnotaccumulatelinearly

–  Randomnessofini.allateralout-of-straightness

70


•  BridgingLoadRequirements

–  Thefollowingequa.oncanbeusedforthebridgingforce:•  Pbr=0.001nPc+0.004Pc√n

•  Pcisthebotomchordcompressiveaxialload

–  ForsmalltomoderatenetupliFandreasonablenumberofjoists,n,Pbratbotomchordisnolargerthanattopchord

–  FormoresevereupliF,Pbratbotomchordcanbecomputedandmaydeterminebridgingsize,orrequirealimitonthevalueofn.

71

External,Addi.onalForcesonBridging•  Cananaddi.onal,externalwindforcebetransferred

throughthejoistbridging?

72

External,Addi.onalForcesonBridging

•  DiagonalXbridgingwouldbeneededinmul.plejoistspacestotransferforcefromthebotomchordleveluptothedeckdiaphragm.

•  Caremustbetakentonotexceedthebirdingconnec.oncapacity,andweldinginaddi.onaltobol.ngmayberequired.

•  Thedeckweldatachmentsalsomustnotbeexceeded.

•  Aseparatestructuralbracemaybemoreadvisable.

73

•  UnbalancedSnowLoads

•  LateralLoadResis.ngSystems

–  DiaphragmandShearWalls

–  BracedFrames

–  RigidFrames

•  LocalWindBracing(Kickers)

•  RoofWindScreens

LateralWindLoads

74

•  Onaroofwitharidge,windstendtoreducesnowloadsonwindwardpor.onsandincreasesnowloadsonleewardpor.ons.

•  Unbalancedroofsnowloadsareapplicableforroofslopebetween2.38degrees(1/2:12)and30.2degrees(7:12)

•  Iftheridgeisalineofsupportforthejoists,theunbalancedsnowneedstobeconsideredinthejoistdesigna.on.

75

UnbalancedRoofSnowLoads

•  Forapitchedjoistthatcreatestheridgeline,theunbalancedsnowloadisnotimplicitlyaccountedforbytheSJISpecifica.ons,soacontractnotetorequireacheckisadvisable.

76

UnbalancedRoofSnowLoads

•  Themostcommonlateralloadresis.ngsystemonstructureswithjoistsandJoistGirdersisadeckdiaphragmandshearwalls.

77

DiaphragmandShearWalls

•  Steeljoistsmaybeusedasdiaphragmchordelements.

•  Steeljoistsmaybecollectorelementsinframelines.

78

DiaphragmandBracedFrames

Con.nuousAngleFieldWeldorScrewDecktoAngleperRoofDiaphragmRequirements

79

DiaphragmBoundary–DeckSupportAngle

Note:ForceVshouldbegivenonthestructuraldrawingsasajoistdesignrequirement.

•  Ifthereisnotadirectloadpathfromadeckedgeangleordiaphragmboundary,thejoistseatmaybesubjectedtoarolloverforce.

80

JoistSeatRollover

81

DiaphragmBoundary

JOISTGIRDERHSS21/2x21/2x3/16CENTERBETWEENJOISTS(NOTBYJOISTMANUFACTURER)

ROOFDECK

PERSIDELAPDIAPHRAGMREQUIREMENTS5/8"DIA.

•  Wherethediaphragmorcollectorchordforceislarge,ashearcollectorcanbeused,betweenthejoistbearingseats.ShownhereisatypicaldetailforK-Series.

82

AlternateDetailtoJoistSeatRollover

JOISTGIRDER

ROOFDECK

5"

PERSIDELAPDIAPHRAGMREQUIREMENTS5/8"DIA.

CHANNELC5x6.7CENTERBETWEENJOISTS(NOTBYJOISTMANUFACTURER)

3/16"

•  Hereisasimilardetail,forusewithLH/DLH-Seriesjoists.

83


•  ButmaybeC5x6.7isnotthebestchoice.

•  Theshearcollectormustcoincidewithalowdeckflute.

•  5”HSSmightbeabeterop.on.

84


•  ChordForcesarecarriedasaddi.onalaxialloadsbythetopchordsofjoistsand/orJoistGirders.

•  ChordForcesmayvaryfromoneendofthechordtotheother.Theaddi.onalaxialloadforeachjoistand/orJoistGirdermustbeindicated.

•  TypeandmagnitudeofaxialforcesatthejoistandJoistGirderendsupportsshallbeshownonthestructuraldrawings.

•  AvoidresolvingjoistorJoistGirderaxialforcesthroughthebearingseatconnec.on.

85

ChordForces-Axial

F F

86

DiaphragmChord

•  JoistorJoistGirdertopchordaxialloadsaretypicallynoteddirectlyontheframingplan.

AXIAL=+/-18K24LH11

AXIAL=+/-72KW24X104

87

AxialLoads

•  Foraxialcollectorloads,toavoidunnecessarytransferdesignoranRFIfromtheJoistManufacturer,itishelpfultoshowthemagnitudeoftheaxialloadatthebuildingperimeter.

AXIAL=0kips(Theaxialloadaccumulatesfromthisend)

88

AxialLoads–BoundaryCondi.ons

Alltopchordaxialloadsandendmomentsshouldbetransmiteddirectlyvia.eplatesor.eangles.Theeccentricityofhorizontalforcestransferredthroughthebearingseatsisthenavoided.

e

F

F

M

89

WindAxialLoadTransfer

TopChordofJoist

90

JoistTiePlate

TopChordofJoist

91

JoistTieAngles

•  Notetheorienta.onofthe.eangles,toavoidthejoistendwebs,intheeventtheyareoutsidethatchordanglesratherthaninthechordgap.Thisalsoallowsforadown-handfieldweld.

92

JoistTieAngles

•  IfajoistisusedintheXbracedframebay,theaxialloadwilltravelthroughthewebsandbotomchord,inaddi.ontothetopchord.

93

XBracedFrame

•  Aten.onisrequiredforthecollectorjoisttobracedframebaytransferconnec.on.

Inthiscase,a“typical”detailneglectsthefactthatthereisactuallyacollectorjoistonthissideofthecolumn.

94

XBracedFrame

95

BracedFrameandCollectorJoist

•  Thisisagood,completedetail.

96

BracedFrameandCollectorJoist

•  TheSpecifyingProfessionalisresponsiblefortherigidframedesign.

•  TypeandmagnitudeofendmomentsatthejoistandJoistGirderendsupportsshallbeshownonthestructuraldrawings.

•  AvoidresolvingjoistorJoistGirderendmomentsthroughthebearingseatconnec.on.Thetopchorddetailscanbesimilartothoseshownforthetransferofaxialloads.

97

RigidFrames–EndMoments

•  Thetopandbotomchordmomentconnec.ondetailsshallbedesignedbytheSpecifyingProfessional.ThejoistdesignershallfurnishtheSpecifyingProfessionalwiththejoistdetailinforma.onifrequested.

•  Unlessspeciallydesignedanddetailedaswindonlyflexibleconnec.ons,rigidframeac.onwillinduceliveloadmoments,whichneedtobespecified.

98

RigidFrames–EndMoments

•  TheSJIhasseveraltoolsavailableforframedesign:

–  VirtualJoistGirderandVirtualJoisttablesforinser.oninstructuralmodelingprograms.

–  Aseriesofdesigntoolsformomentconnec.onswithvariouscolumnconfigura.ons.

99

SteelJoistIns.tuteTools

•  Anaddi.onalresourceistheSteelJoistIns.tuteTechnicalDigest#11,DesignofLateralLoadResis;ngFramesUsingSteelJoistsandJoistGirders

100

LateralLoadResis.ngFrames

•  SpecifyingProfessionaltoprovidehorizontalandver.calcomponentsofwindbracingforcesbeingtransmitedtojoists.

101

WindBracingKickers

•  Thisexampledoesnotincludeahorizontalcomponent,butwithASD,assump.onscanbemadeaboutanaddedaxialwindloadcontrollingthejoisttopchorddesign.

•  Itwouldbehelpfultohaveguidanceastotheloca.onoftheload.

Connectattopchordpanelpointclosestto3’-0fromendofjoist.

102

WindBracingKickers

•  Thelateralhorizontalforcewillbeassumedtotransferintothedeckdiaphragmandthejoistwillnotbedesignedforalateral,out-of-planeload.

103

WindBracingKickers

•  Thisisanexampleofanendwallcondi.on,withaseriesofwindbraceloadsalongthejoistspan.

104

WindBracingKickers

•  Wherewindforces“kicker”tojoistandcreatever.calcomponentloads,referenceIBCfordeflec.oncriteria

f. The wind load is permitted to be taken as 0.42 times the “component and cladding” loads for the purpose of determining deflection limits herein.

f

105

WindBracingKickers

•  Windcreatesanoverturningmomentfromroofscreens.

•  Abracingmembercanbeusedtoresolvetheoverturningeffect,crea.ngver.calwindloadsontheroofjoists.

106

RoofScreens

•  Wherethewindscreenpostisnotbraced,andthescreenisperpendiculartothejoists,itisbesttoextendthepostandatachtoboththetopandbotomchord,resolvingtheoverturningmomentintoacouple.

107

RoofScreens–PerpendiculartoJoist

ReplacewithKeith’ssec.oncut

•  Wherethewindscreenpostisnotbracedabovetheroof,andthescreenisparalleltothejoists,thejoistscannottakeatorsionalload.

–  Itisbesttoextendthepostandatachtoboththetopandbotomchord,resolvingtheoverturningmomentwithbracingmembersbelowtheroof.

108

RoofScreens–ParalleltoJoist

•  Single-plymembraneroofingisthemostcommonsystemabovesteeljoists.

•  Thesingle-plymembranemaybefullyadhered.

•  Alternately,andincreasingly,aseam-fastened,mechanically-atachedmethodofinstalla.onisbeingu.lized.

•  Since2000,thewidthofthemembranerollshasbeenincreasingdrama.cally.

109

MechanicallyFastenedMembraneRoofs

FromtheNa.onalResearchCouncilofCanada 110


•  Withthisinstalla.onmethod,thesingle-plymembranesheetismechanically-atachedalongitsouteredgesintotheroofdeck,whichresultsinalargertributaryupliFloadperfastenerandfastenersbeingplacedinlinear,non-uniformloadingconfigura.onsoftheroofdeckandunderlyingsuppor.ngstructure

•  Thedirec.onalityoftheseamsrela.vetojoistanddeckspandirec.onisusuallynotknownorcontrolled.

111


FromtheNa.onalResearchCouncilofCanada

•  Windtunneltest

112


FromtheNa.onalResearchCouncilofCanada

•  Windtunneltest

113


•  Thetributarywidththatcreatesthe“lineloading”caneasilybecometwicetheactualjoisttributarywidth.

114

DeckandJoistLoading

•  Typically,theroofingmembraneisnotconsideredinstructuralcontractdocuments.

•  Theroofingmembranespecifica.oncanbevague,withreferenceslike“atachpermanufacturerrecommenda.ons”.

•  AdesignforuniformloadsmaynotbeadequatewhereinfacttheupliFwillbeappliedaslinearloads.

•  FMGlobalDataSheet1-29nowprovidesseparatetablesfordeckspanswhenthedistancebetweenroofcoverfastenersismorethanone-halfthedeckspan.

•  Afullyadheredroofmembranemaybethebestop.onfromastructuralperspec.ve.

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JoistDesignforMembraneRoof

•  TheupcomingversionofASCE7-16islikelytoincludenewroofupliFzonepaternstomoreaccuratelydepictbehavior

–  Twoedgezones–  “L”shapedcornerzones

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ASCE7-16Preview

•  Thepressurecoefficientsarelikelytochange

–  Black,solidline:7-10–  Red,dashedline:7-16

•  Ingeneral,morepressureatcornersandedges;lesspressureatinteriorfieldandwithlargerwindeffec.veareas

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ASCE7-16Preview

•  Morewindpressureat100squarefooteffec.vewindarea

•  Tablesmaynotprovidevaluesbeyond100squarefeet

•  Somoredetailedanalysismaybeadvantageous,asmostjoistsexceed100squarefooteffec.vewindarea

118

ASCE7-16Preview

•  The44thEdi.onCatalogiscomingsoon.

•  Formoreinforma.onorupdates,visittheSJIwebsite:www.steeljoist.org

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SteelJoistIns.tute

Wind Design Consideraxons for Joists and Joist Girders - NET

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