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PDHonline Course S184 (2 PDH)

Flexible Metal Deck Roof Diaphragms

Instructor: D. Matthew Stuart, P.E., S.E., F.ASCE, F.SEI , SECB, MgtEng

2013

PDH Online | PDH Center

5272 Meadow Estates DriveFairfax, VA 22030-6658

Phone & Fax: 703-988-0088www.PDHonline.orgwww.PDHcenter.com

An Approved Continuing Education Provider

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www.PDHcenter.com www.PDHonline.org

D.MatthewStuart 1

Sheardiaphragmsareessentiallyplanarstructuralsystemsfoundinroofs,floors,andwallsof

buildings. Theyarecomprisedofinterconnectedunits,attachedtosupportingmembers,such

thattheentireassemblypossessesbothinplaneshearstrengthandstiffness.Themajor

components

of

a

diaphragm

include

the

individual

deck

panels,

the

structural

members

to

which

theyareconnectedandtheconnectingdevicesorfasteners. Fastenertypesincludewelds,

screws,powerdrivenpins,orothermechanicaldevicesthathaveapredictablecapacity. The

strengthandstiffnessofadiaphragmdependsonthepanelproperties,thespanarrangements,

andthequalityoftheconnections.

Figure1illustratesthebasicconceptforaroofandwalldiaphragm.InFigure1windpressureon

thewallsparalleltolengthLactonthebuilding. Alineloadreactionofthispressureis

distributedto

the

top

of

the

wall

at

the

roof

plane

via

the

vertical

spanning

capacity

of

the

claddingoverheightH. Theroof,actingasasimplespanhorizontalgirderofdepthB,distributes

thewindlineloadasashearreactionalongthetopoftheendwallsperpendiculartoL. Theend

wallsinturnactasdiaphragmsbetweentheroofandfoundationlevels.

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D.MatthewStuart 2

Fortheroofinthisexample,thetotaluniformloadonthediaphragmequalsthecombined

effectsofthewindwardandleewardcladdingreactions(ww +wL). The maximumendreaction(R)

oftheroofdiaphragmthereforeis((ww +wL)xL)/2. RdividedbylengthBequalsthecollector

load

or

maximum

uniform

shear

force

in

the

diaphragm.

The

maximum

roof

diaphragm

moment

(M)equals((ww +wL)xL2)/8. Thecorrespondingdiaphragmchordforcesarethereforeequalto

MdividedbythediaphragmdepthB. Themaximumunitshearonthewalldiaphragmisalso

equaltotheroofreaction,R,dividedbyB. However,thewalldiaphragmmomentequalsRxH.

Itshouldalsobenotedthat:

a. Adiaphragmactslikeashortdeepbeam.

b. Themaximumaverageshear(R/B)occursattheendsoftheroofdiaphragm.

c. Zonesnearthemidspanoftheroofaresubjectedtolessunitshearthereforeless

diaphragmstrengthisrequired.

d. Thelargerdesignshearsmayberesistedbyusingbothheaviergagepanelsandfewer

connectionsorbymorefrequentlyconnectedlightergagepanels.Thereforethemost

efficientuseofmaterialsmaynotbemetbyusingasinglediaphragmdesignforthe

entireroofarea. However,fromapracticalconstructabilitystandpointitismore

commonto

use

asingle

deck

and

connector

type

over

an

entire

roof

and

increase

the

frequencyoftheconnectorsinordertoresistgreaterinplaneshearforces.

Roofdiaphragmsmaybeassembledfrom

awidevarietyofpanelprofilesincluding

NarrowRib

(NR),

Intermediate

Rib

(IR)

and

WideRib(WR). Eachofthesedifferent

decktypesaredescribedintheSteelDeck

Institute(SDI)PublicationNo.31,Design

ManualforCompositeDecks,FormDecks

andRoofDecks. Roofdiaphragmpanels

typicallyvaryfrom0.0295inchesto0.064

inchesinthicknessandcomeinwidthsof

18inchesto36inchesormore.

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D.MatthewStuart 3

Adiaphragmshouldbedesignedandassembledtocoveraspecifiedareainsuchawaythatin

planeshearstrengthandstiffnessispredictable. Theprincipalelementsdeterminingthese

factorsincludespacingofthesupportframing,thesizeandthicknessoftheindividualdeck

panels

and

the

interconnecting

fasteners.

A

metal

roof

deck

diaphragm

is

a

fairly

flexible

system

somewhatanalogoustoatrussasshowninFigure2. Priortoinstallingthetrussdiagonalor

attachingthediaphragmtothesupports(andeachadjacentsheetviasidelapconnectors),

neitheroftheframespossessmuchstrengthorstiffness.Theshearstrengthofadiaphragm

systemislimitedbythestrengthofconnections,localpanelbucklingandthegeneralplatelike

bucklingcharacteristicsoftheentirediaphragmarea.

Inadditiontoneedingtoresistplanarshearforces,inorderforadiaphragmtofunctionproperly

itisalsonecessarytoprovidemembersalongtheextremeedgesofthedeckasrequiredtoresist

theflexural

tension

and

compression

components

of

the

deep

beam

member.

This

is

analogous

tothetopandbottomchordsofatrussresistingthecompressionandtensionforcesofthe

member.

Source: CSI

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D.MatthewStuart 4

Thestrengthofadiaphragmcanalsobelimitedbyproperattentiontotheedgeandend

terminationconditions.Inaddition,atinteriorpositions,panelsmustbesufficientlyoverlapped

toprovideadequateenddistancesfortheconnectorused.Ifpanelsarebuttedattheirends

rather

than

end

lapped,

as

is

common

with

floor

decks,

then

each

panel

must

be

individually

connectedatitsendswiththespecifiedpattern.

Theoverlappingedgesofpanelsshouldbeinclosecontactinordertominimizetheeccentricity

. . ,

usedattheoverlapconditionshouldalsobeinstalledontheedgepanelatthediaphragm

perimeterwherethesidelapconnectorwouldnormallyoccuriftherewereanotheradjacent

panel. Otherwisetheshearstrengthalongthefirstinteriorsidelapmayexceedthatalongthe

perimetermemberthusdiminishingthecontributionofthedeckendconnectionatthe

supportingshearwallorverticalXbracedframe.

Source: TataSteel

Establishingwhat

type

of

fastener

is

to

be

used

is

acritical

component

of

designing

and

detailing

adiaphragm.Fastenerscommonlyincludewelds,screwsandpowderdrivennaillikepins.

Structuralconnectionsincludefastenersthatconnectoneormoresheetstoheavierorthicker

frameorstructuralmembers. Sidelapconnectionsincludefastenersthatconnectadjacentpanels

toeachotherandnottothesupportingframemembers. Stitchconnectionsareanothername

forsidelapconnections.

Fasteners

Source: Hilti;MetalDeckSupply;HobartBrothers

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D.MatthewStuart 5

Arcspotwelds,orpuddlewelds,areproducedbystrikinganarcontheuppersheet,thereby

causingaholetoform,whilethelowersheetisbeingraisedtofusiontemperature. Withthe

attainmentof

the

proper

temperature,

the

electrode

is

moved

in

acircular

pattern

until

the

hole

isfilledandfusionattainedonthearcpuddleperimeter. Therelativestrengthinaseriesofwelds

canvarysignificantlybymodestchangesinweldingtimes.

WeldedConnections:

rcspotwe stostructura mem ers .e.we ngo t nners eetstot c erstructura

members)requiredirectcontactbetweentheunitsforproperheattransfer. Inaddition,aproper

balancebetweentheweldingtimeandtheelectrodeburnoffrateisessentialtogoodquality

welding.Weldingmachinepowersettingsrequiredusuallyarewellbelowthoseneededfor

weldinginhotrolledsteels. Thetimerequiredperweldmayvarybetween3and6secondsor

moredependingofthepropertiesofpartsbeingconnected.

Source: PalmBeachCountySchools

Weldwashersfunctionasaheatsinkallowingholeformationinthinnerpanelswithoutexcessive

growthofthehole,asthetemperatureoftheunderlyingpanelisincreased. Thewasheris

subsequentlyfilled

with

the

weld

stem

growing

into

the

lower

panel

which

becomes

anchored

on

thewashersholeperimeter. Uponcooling,thewasherisclampeddownontheattachedsheet.

Weldwashersarerecommendedforpanelsthinnerthan0.0280inches.

Source: MetalDeckSupply

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D.MatthewStuart 6

AllweldsshouldbemadebyqualifiedoperatorsfollowingAWSD1.3Specifications.Asindicated

previously,weldingthinmaterialusuallyrequiresamuchlowerpowersettingandlowerburnoff

ratethanwithheavysteelunits. Particularcareisalsorequiredwhenweldingdecktojoistsin

ordertoavoiddamagetothejoistchords.Preliminaryfieldqualitycontrolcheckscanbemadeby

placingapair

of

welds

in

adjacent

valleys

at

one

end

of

apanel.

A

visual

inspection

will

show

if

theweldmaterialisfusedproperlyandincontactwiththeunderlyingpanel. Intermittent

contactmayindicateexcessivepowersettings. Separationbetweenthepanelsmayindicate

insufficientweldingtimeandpoorfusion. Theterminationoftheweldingoperationmaynot

.

thanthreequartersoftheweldperimeter.

Inadjacentdiaphragmpanelswithnestableorflatoverlappingedges,sheettosheetorstitch

connectionsaretypicallyrequiredawayfromthesupportingmembers. Theplacementofarc

spotweldsatsuchsidelapsisdifficult. Inaddition,thethinnerthematerial,themoredifficultthe

weldingoperationbecomes. Weldingofsidelapsisnotrecommendedformaterialof0.0295inch

orthinner. Theamountofslipormovementexperiencedasweldsareloadedinshearinthin

steelelementsisverysmallrelativetothatformostothermechanicalconnectors. The

movementisessentiallylimitedtopaneldistortionaroundtheweld.

SidelapScrewConnector

Source: Bondek

Screwsmust

be

installed

using

properly

calibrated

tools

in

order

to

avoid

overdriving

which

can

stripthethreadsatsidelapsorseverthescrewwhenitisplacedintoathickersupporting

member. Thequalityofscrewconnectorsingeneralistypicallynotamajorproblemalthough

thesetypesofconnectorscansometimesfracturewhenbeingdrivenintoathickersupporting

material. Themostcommonproblemwithscrewconnectorsinvolvesallowingthescrewto

threadupontheuppersheetbeforebecomingengagedinthelowersheetthusleavingmajor

ScrewConnections:

gapsbetweentheseparatepanels. Suchscrewsshouldberemovedandredrivennearbywhile

forcingsheetlayerstoremainindirectcontact.

Source: Simpson

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D.MatthewStuart 7

Powderdrivenfastenersmustbeinstalledfollowingthemanufacturersrecommendations. Care

mustbeexercisedinsettingthedrivingforcetoobtaintheproperdepthofpenetration. Once

drivenproperly,thesenaillikefastenersareveryresistanttoextractionbyupliftforces. Inuplifttestsonsheetmaterial,theusualmodeoffailureinvolvestearingthesheetaroundtheheador

washerleavingthefastenerinplace.

PowderDrivenFasteners:

Source: Hilti

Thequality

of

button

punching

is

difficult

to

maintain

because

the

attachment

depends

on

the

careandtheenergyusedbytheinstallerandthetoolthatisused.

ButtonPunchedSidelaps:

Source: Metaldeck.com

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D.MatthewStuart 8

1. Strengthvs.Cost:Itistypicallybettertoachievetherequireddiaphragmstrengthwitha

greaternumberofweakerbutlessexpensivefasteners. Howeveritisrecommendedthatthe

designershouldcheckthedeflectionofthediaphragm.

2. Theinsurancefireratingorwindupliftrequirementsofabuildingmaynotallowa

Miscellaneous:

.

3. Thecommonavailabilityofanygivendeckattachmenttool,equipmentorpowersourcemay

dictatethechoiceoffastenerforanygivenproject.

4. Theexposedundersideappearanceofthedeckmaybeimportant. Ifappearanceiscritical

sidelapscrewsorevenveryweakbuttonpunchesmayberequiredeventhoughanincreased

numberoftheseconnectorswouldbeneededoverthatprovidedbywelding.

5. Atthistimetherearenostandardtestsforupliftloadingsonfasteners. However,uplift

failureofadeckpanelunderserviceloadingisveryuncommon. Thisisbecausethespacing

offasteners

as

dictated

by

diaphragm

design

or

insurance

requirements

(Factory

Mutual

or

UnderwritersLaboratories)typicallyexceedsanynetupliftforces.

Fasteningof

metal

deck

to

the

supports

at

one

time

was

only

done

by

welding

until

self

drilling

screwsbecameavailable. Inaddition,weldingofdeckhasalsobeenreplacedtosomedegreeby

fastenersthatareshotin(eitherairorpowderactuated). Allthreeofthesemethodsof

attachmentperformthesamefunctionofholdingthedeckinplaceandthusallowingshear

strengthandstiffness(thatcanbepredicted)tobedeveloped.

HowtoFastenSteelDeck

Becausetheconnectionofthedeck(bothsidelapsandtothesupports)isaveryimportant

componentofthediaphragmcapacity,forbothstructuralstabilityandinsuranceandfirerating

approvals,itisuptothedesignertochoosethecorrectfastenerstobespecifiedandbeableto

judgethemeritsofsubstitutionsrequestedbythecontractor.

Source: BarsinProducts

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D.MatthewStuart 9

Welding,whenproperlyexecuted,providesthestrongestandstiffestdeckconnections. Welding

alsorequires

the

most

skill

and

therefore

should

be

inspected

thoroughly.

Because

most

visible

welddiametersusedwithsteeldeckarebetweeninchesandinchesneitherAISInorAWS

capacityformulasshouldbeused. However,testingperformedbytheSDIhasestablished

strengthsforwelddiametersbetweeninchandinches. Theultimatestrengthformulawas

determined to be that shown on this slide. The corres ondin AISI formula indicates that reater

WeldedConnections:

.

weldstrengthscanresultwithmultiplemetalthickness(suchasatoverlaps),howevertheSDI

testssuggeststhatformetaldeckthiseffectshouldbeignored. TheSDIalsorecommends,based

onthedistributionofthetestresults,thatasafetyfactorof2.75beusedfortheseweldsrather

thanasafetyfactorof2.56assuggestedbytheAISISpecifications.

Qf =2.2*t*Fu *(dt)[inkips]

Where: d=averagevisiblediameter[inches]

Fu =steelstrength[ksi]

t=basemetalthickness[inches]

Itisgoodpracticetouseweldwashersfordeckswithametalthicknesslessthan0.0280inches.It

isalsorecommendedtouse5/8inchpuddleweldswithoutwashersformaterialthicknesses

greaterthan

0.0280

inches.

In

no

case

should

washers

be

used

on

interior

sidelaps.

Inadjacentdeckpanelswithnestableorflatoverlappingedges,sheettosheet(stitch)

connectionsarerequired. Theinstallationofarcspotweldsatsidelapscanbeproblematic. In

addition,thethinnerthematerial,themoredifficulttheweldingoperation. Weldingofsidelaps

. .

Source: Cordeck

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D.MatthewStuart 10

Screwconnections,suchasBuildexTEKSscrews,maybeeitherselfdrillingortheselftapping

typethat

requires

apredrilled

hole

prior

to

installation.

The

most

commonly

used

screw

size

to

attachdecktobarjoistsorstructuralsteelareNo.12andNo.14. SmallerNo.8andNo.10

screwsaremorecommonlyusedforsidelapconnections.

ScrewConnections:

enconnec ng nme a ec o c ers ruc ura mem erssuc as ar o s sor eam

flanges,littledifferenceexistsintheshearstrengthforNo.12andNo.14screws. Thisisbecause

thefailuremodeofthedecktendstoinvolvearolluporcrushingofthedeckonthebearing

sideofthescrewwithfracturelinessubsequentlydevelopinginthedecking.

Forstitchconnectionsbetweensheets(atthesidelaps)adifferenttypeoffailureoccurs. The

screw,whennotanchoredintoathickermorerigidelement,tipsovermoreeasilyandismore

flexible. Althoughtheresultingstrengthmaybelimitedbybearingandtearinginthemetaldeck,

withsufficientrotationofthesidelap,acombinedtearingandpulloutfailuremayalsooccur.

TheSDIscrewstudiesindicatethatstitchscrewshearcapacityisindependentoftheyield

strengthof

steel

deck

that

is

commonly

used

for

flexible

diaphragms.

The

most

common

prematurefailureproblemwithsidelapattachmentsoccurswhenthescrewisallowedtothread

upontheuppersheetbeforebecomingfullyengagedinthelower,thuscreatingmajorgaps

betweentheadjacentunits. Suchimproperlyinstalledscrewsshouldberemovedandredriven

whileforcingtheoverlappingsheetstoremainincontact.

Metaldeck

to

structural

support

connections

can

also

be

made

by

using

nail

like

fasteners,

driven

eitherpneumaticallyorwithpowderactuatedtools. Suchfastenersaremadefromhardened

steelandusuallyhaveaheattreatedshafttoenhanceanchorage. Theshaft,whichmayhavea

slighttaper,canbefittedwithwashers,concavetothedrivingdirectiontoabsorbthefinaldriving

energyandclampthesheetinposition.

PowderDrivenFasteners:

Sincetherearenopredrilledholesrequiredwiththesetypesofconnectors,theinstallation

processdisplacesmaterialandleavesitlockedunderthewasher,resultinginverystiff

connections. Thedrivingdepthiscontrolledbythepowerselectionforthetoolused. Fastener

strengthisinfluencedbythedrivingdepth.TestsconductedbyWestVirginiaUniversityalso

indicatethatthethicknessoftheunderlyingmaterialhasnoeffectonshearstrengthsincethe

thinnersheetmaterialwillcontrolperformance.

Adrivenfastenershouldbeinstalledsotheheadprojectsoutward,fromtheattachedpart,to

m sse y emanu ac urer. eax so e as enermus eperpen cu ar o es ee pr or

todriving,

usually

within

plus

or

minus

10

degrees

of

vertical.

In

addition,

it

is

recommended

that

edgeandendfastenershaveaminimumsidelapedgedistanceof3/8inchandaminimumend

andendlapdistanceof1inch.

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D.MatthewStuart 11

Incertainpanels,oneedgehasanupstandingsingleelement,whiletheoppositesidehasa

foldedover

double

element.

As

panels

are

placed,

the

single

element

is

inserted

into

the

double

element,producinganupstandingsidelapthatcanbebuttonpunchedtoprovideinterlockingof

thetwoadjacentsheets.

ButtonPunchedSidelaps:

an opera e punc ng oo ormsa ree ayernes o sma cones a s e nas g y

loosestate,becauseofelasticrebound,astheformingforceisremoved.Manualbuttonpunched

sidelapsdostabilizepaneledgesbutcontributelittlediaphragmstrengthastheycanvarygreatly

inshapeandeffectiveness. Thequalityofhandinstalledbuttonpunchesisdifficulttomaintain.

Theattachmentdependsonthecareandtheenergyusedbytheinstallerandthetoolused. A

safetyfactorofthreeisrecommended.

Atconditionswherejoistsspanperpendiculartoandterminateatashearwall,theedge

mostdiaphragm

panel

may

not

be

in

direct

contact

with

the

wall.

At

these

conditions

the

requiredperimeterdiaphragmconnectionscanbeaccomplishedbyinstallingablockspacer

orcollectoralongthetopofthewallbetweenthejoiststhatmatchesthedepthofthe

bearingassembly. Acontinuousangleattacheddirectlytothetopofandperpendicularto

thejoistmayalsobeusedaslongasthebearingassemblyofthejoistsiscapableof

Miscellaneous:

.

AllowableloadtablesareavailablefromtheSDIandanumberofdifferentdeck

manufacturers. Loadtablesaretypicallycategorizedbythemeansofconnection,thepanel

widthandthickness,spanlengths,thefasteningpatternandthetypeoffastenerandsidelab

connector.

Thestiffnessofadiaphragmisadirectindicationofhowsusceptiblethedeckistodistortions

undertheinfluenceofinplaneshearforces. Theneedtoknowthemagnitudeofmovement

isparticularlyimportantwhenassessingthetransferofforces,throughadiaphragm,

betweenadjacentframesorshearwalls. Inaddition,thehorizontaldeflectionofthe

diaphragmcanhaveanimpactontheswayofexteriorcladdingmembers,suchasprecastor

tiltuppanels,inadditionaltothelocalizedflexuraldeflectionofthesameasaresultofwind

loadsperpendicular

to

the

span

of

the

diaphragm.

Steeldeckdiaphragmsmaybereinforcedwithoverlaymentssuchas insulatingconcrete,

structuralconcrete,orbydirectlyattachingflatpanelssuchasplywoodtoproduceaflat

surface. Thesupplementalmaterialprovidesadditionalpathsthroughwhichshearforces

maytraversethediaphragm.

Itisalsopossibletoinstallhorizontaldiagonalsteelbracingorstrapsbeneaththedeckin

ordertosupplementorsupplanttheshearcapacityofthedeck.

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D.MatthewStuart 12

Thefollowingdesignexampleisforasimpleonestoryrectangularbuildingexposedtoatotalwindwardandleewardpressureof35PSF. Itshouldbenotedthatinthisexamplethewindwardandleeward

pressurereactions

at

the

top

of

the

cladding

and

along

the

edge

of

the

diaphragm

are

shown

as

acombinedlineloadof245PLF.

Asindicatedintheexample,thediaphragmreactionof16.54kipsisdividedbythelengthoftheendwalltoarriveattheunitcollectordiaphragmshearforceof367.5PLF. Atthesametimeashear

DesignExample

fastenerzonesasrequiredtosatisfythevaryingmagnitudesofplanarshearresistance resultingfromtheimposedloads.

AnAllowableDiaphragmShearStrengthTable(availablefrommostoftheroofdeckmanufacturesaswellastheSDI)isthenreferredtoinordertoassessthemostappropriatefastenerspacingfortheappliedloads.Inthisexample,36inchwide,1inch,TypeB,22Gagemetalroofdeckusing5/8inchpuddleweldsand#10TEKscrewsidelapfastenershavebeenpreselectedasthetypeofdeckandfastenerstobeused.ItshouldbenotedthatthecapacitiesintheShearStrengthTablealreadyincludea1/3increaseforwind.

Forajoistspacingof6feetandapreselectedweldpatternof4uniformlyspacedpuddleweldsacrossthe36inchwidepanel,ashearcapacityof374PLFcanbeobtainedusing8uniformlyspacedsidelapscrewsalongthe6feetspanofthedeck.Thisvalueisgreaterthanthe367.5PLFendshearreactioncalculatedintheexample.

Nextatanarbitrarylocationapproximatelyofthediaphragmspanfromtheendsupportwallisanalyzedinordertoallowforareductioninthenumberoffastenersoverthemiddlehalfoftheroof.Theequivalentuniformshearloadatthislocationonthediaphragmis193PLF.ReferringagaintotheAllowableShearStrengthTableindicatesthatusingaweldpatternof3uniformlyspacedpuddleweldsacrossthe36inchwidepanel,ashearcapacityof193PLFcanbeobtainedusing2uniformlyspacedsidelapscrewsalongthe6feetspanofthedeck.

Detailingoftheconnectionofthemetalroofdecktotheendshearwallsisnotcoveredinthisexample,howevertypicallyacontinuousembeddedsteelplateinthetopofthewallwouldbeprovidedinorderforthedecktobesecuredtothetopofthewall.

Shearinthedeckdiaphragmisalsocheckedforwindloadsagainsttheshortsideofthebuildinginwhichthediaphragmonlyhastospan45feetbetweenthe135feetlongCMUshearwalls.Thecalculatedmaximumunitcollectordiaphragmshearforceof41PLFislessthantheminimum193PLFshearcapacityofthedeckintheotherorthogonaldirection,thereforethefastenerpatterndevelopedinthefirstpartoftheexampleisadequateforwindloadsintheoppositedirection.However,asthe

joistbearingassemblyseparatesthetopedgeofthedeckfromtheCMUshearwallitisnecessaryforthecollectorforcetobetransmittedfromthediaphragmtothetopofthewallthroughthejoistbearingassemblies.Amaximumrolloverforceof246poundsiscalculated ateachjoist,whichislessthanthetypicalindustrystandardjoistbearingassemblycapacityof1,650pounds,thereforenocollectorblockisrequiredbetweeneachjoisttotransfertheshearforcestothetopofthewall.

Inorderforthediaphragmtofunctionproperly,inadditiontoananalysisoftheplanarshearforces,itisnecessarytoprovidechordmembersalongtheextremeedgesofthedecktoprovideresistancetotheextremeflexuraltensionandcompressioncomponentsofthedeepbeamdiaphragmanalogy. Forthisexamplethemaximumchordforceiscalculatedasfollows:

Mmax=((245PLF)*(135FT)2)/8=558.14KipFeet;ChordForce=558.14KF/45FT=12.4Kips

Assumingthat

compression

controls,

the

maximum

allowable

compressive

stress

of

10.14

ksi

is

calculatedfora36ksi,continuousL3x3xbracedat6feetoncenterwereitisconnectedtothetopofthejoistbearingassemblies.Theactualcalculated compressivestressof8.61ksiintheL3x3islessthantheallowable.Itisimportanttounderstandthatthischordmembermustbeprovidedalongboth135feetlongedgesofthedeckwithbuttweldsprovidedatalljointsoftheL3x3.Thechordmemberforwindforcesintheoppositedirectionisprovidedbythecontinuousembeddedsteelplatelocatedinthetopofthe45feetlongendshearwallsasdescribedinthepreviousslide.

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D.MatthewStuart 13

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D.MatthewStuart 14

Source:SDI

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D.MatthewStuart 15

Thefollowingareillustrationsofroofdeckattachmentdiagramsandschedulesfromanexample

project.Thisinformationshouldbeprovidedonallprojectsinordertoprovideclearinstructions

tothedeckinstallerconcerningtherequiredfastenertype,spacingandextent.

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