Construction Methods - Chapter15.pdf - po ang - Januszek66

SteelConstruction

15–1INTRODUCTION

ElementsofSteelConstruction

Structuralsteelconstructionisaspecializedtaskthatisusuallyperformedbyspecialtysub-

contractors.However,constructionmanagersandinspectorsmustunderstandtheprinciples

andproceduresinvolved.Theprocessofsteelconstructioncanbebrokendownintothe

threemajorelementsofadvancedplanning,steelfabricationanddeliverytothejobsite,

andfieldoperations.Eachoftheseelementsinvolvesanumberofoperationswhicharede-

scribedinthischapter.

Forlargeorcomplexprojects,advancedplanningincludesdivisioningthesteeland

planningshippinganderectionprocedures. Divisioning istheprocessofdividinga

structureintounits(called divisions )whichareusedtoschedulethefabricationand

deliveryofstructuralsteelmemberstothejobsite.Sincedivisioningisdeterminedbythe

orderinwhichthestructurewillbeerected,itmustbeperformedasajointeffortofthesteel

fabricatorandtheerectionmanager.Whenplanningshopfabricationsprocedures,

thesizeandweightoflargemembersmustbecheckedagainstplantcapacity,transporta-

tionsizeandweightlimits,andthecapacityoferectionequipment.Inplanningerection

procedures,thetypeofequipmenttobeutilizedandtheprocedurestobefollowedarede-

terminedbythetypeofstructurebeingerectedandtheanticipatedsiteconditions.Lifting

equipment,alignmentrequirements,andfieldconnectionsaredescribedinsucceedingsec-

tionsofthischapter.

FieldOperations

Fieldoperationsincludereceivingandunloading,sorting(or“shakingout”),inspecting,

storing,anderectingthesteel.Theprocessofunloadingsteeltoatemporarystoragearea

andthenmovingitfromstoragetothepointoferectioniscalled yarding. Structuralsteel

membersareoftencarelesslyhandledduringunloadingatthejobsite.Theymaybethrown

offthetruckorrailcarandstackedupinamannerthatwillcausedistortioninthemember

433

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CHAPTER15

Table15–1 Fabricationandmilltoleranceforsteelmembers

Dimensions

Tolerance

Depth

⁄ 8 in.(0.32cm)

Width

+ 1

⁄ 4 in.(0.64cm), −

⁄ 16 in.(0.48cm)

Flangesout-of-square

Depth12in.(30cm)orless 1

⁄ 4 in.(0.64cm)

Depthover12in.(30cm)

⁄ 16 in.(0.79cm)

Areaandweight

± 2.5%

Length

Endcontactbearing ± 1

⁄ 32 in.(0.08cm)

Othermembers

Length30ft(9.2m)orless ±

⁄ 16 in.(0.16cm)

Lengthover30ft(9.2m) ± 1

in.(0.32cm)

Endsout-of-square

⁄ 64 in./in.(cm/cm)ofdepthorflangewidth,

whicheverisgreater

Straightness

General

⁄ 8 in./10ft(0.1cm/m)oflength

Compressionmembers Deviationfromstraightnessof 1

⁄ 1000 ofaxiallength

betweenpointsoflateralsupport

anddamagetoitspaint.Suchpracticesmustbeavoided.Inunloadinglongflexiblemem-

bersandtrusses,doubleslingsshouldbeusedtoavoidbendingthemember.Ifthesteelhas

notbeeninspectedatthefabricationshop,itmustbeinspectedafterunloadingforconfor-

mancetotheshopdrawingsandthetolerancesspecifiedinTable15–1.Camberandsweep

ofbeamsareillustratedinFigure15–1.Inanycase,membersmustbecheckedatthejob

siteforpossibleshippingandunloadingdamage.

Shakingout steelistheprocessofsortingitoutbyidentifyingeachmember,andstor-

ingitinsuchamannerthatitcanbeeasilyobtainedduringerection.Codenumbersareof-

tenpaintedonthememberstofacilitateidentificationduringerection.Steelshouldbe

storedoffthegroundonplatforms,skids,orothersupports,andprotectedfromdirt,grease,

andcorrosion.Erection,thefinalelementoffieldoperations,isdescribedinSection15–3.

15–2STRUCTURALSTEEL

TypesofSteel

ThetypeofsteelcontainedinastructuralsteelmemberisdesignatedbytheletterAfol-

lowedbytheAmericanSocietyforTestingandMaterials(ASTM)designationnumber.The

principaltypesofstructuralsteelinclude:

•A36CarbonStructuralSteel.

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STEELCONSTRUCTION

Figure15–1 Camberandsweepofbeams.

•A572High-StrengthLow-AlloyStructuralSteel.

•A588Corrosion-ResistantHigh-StrengthLow-AlloyStructuralSteel.

Steelstrengthisdesignatedbythesymbol F y , whichindicatestheminimumyieldpointof

thesteelexpressedinthousandsofpoundspersquareinch(ksi),poundspersquareinch

(psi),ormegapascals(MPa).TypeA36steelhasayieldstrengthof36ksi(36,000lb/sqin.

or248.2MPa).Thehigh-strengthsteels(typesA572andA588)areavailableinyield

strengthsof42ksi(289.6MPa)to65ksi(448.2MPa).

Weatheringsteel isatypeofsteelthatdevelopsaprotectiveoxidecoatonitssurface

uponexposuretotheelementssothatpaintingisnotrequiredforprotectionagainstmost

atmosphericcorrosion.Thatnaturalbrowncolorthatdevelopswithexposureblendswell

withnaturalsettings.However,caremustbetakentopreventstainingofstructuralelements

composedofothermaterialswhicharelocatedinthevicinityoftheweatheringsteeland

thusexposedtotherunofforwindblownwaterfromtheweatheringsteel.

StandardRolledShapes

Thereareanumberofrolledsteelshapesproducedforconstructionwhichhavebeenstan-

dardizedbytheAmericanSocietyforTestingandMaterials.Figure15–2illustratesfive

majorsectionshapes.AlistofstandardshapesandtheirAISCdesignationsisgivenin

Table15–2.Notethattheusualdesignationcodeincludesalettersymbol(identifyingthe

sectionshape)followedbytwonumbers(indicatingthesectiondepthininchesand

theweightperfoot).Designationsforangles,bars,andtubesareslightlydifferent,inthat

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CHAPTER15

Figure15–2 Rolled-steelsectionshapes.

Table15–2 Rolled-steelshapedesignations

TypeofShape ExampleDesignation

Wshape W27 × 114

Sshape S20 × 95

Mshape M8 × 25

AmericanStandardChannel C12 × 30

MiscellaneousChannel MC12 × 50

HP(bearingpile)shape HP14 × 89

Equallegangle

L6 × 6 × 1

⁄ 2

Unequallegangle

L8 × 4 ×

Structuralteecutfrom:

Wshape WT8 × 18

Sshape ST6 × 25

Mshape MT4 × 16.3

Plate

PL 1

× 12

Squarebar

Bar2 "

Roundbar

Bar2 φ

Flatbar

Bar2 ×

Pipe

Pipe6std.

Structuraltubing

Square

TS6 × 6 × .250

Rectangular

TS6 × 4 × .250

Circular

TS4OD × .250

thenumbersusedidentifyprincipalsectiondimensionsininchesratherthanthesection

depthandweight.Detailedsectionpropertiesaswellastheweightofpipe,plates,andcrane

railsaregiveninreference3.

Built-UpMembers

Girdersareusedwhenregularrolledshapesarenotdeepenoughorwideenoughtoprovide

therequiredsectionproperties.Plategirders(Figure15–3a)normallyconsistofaweband

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STEELCONSTRUCTION

Figure15–3 Built-upsteelmembers.

Figure15–4 Open-websteeljoist.

topandbottomflanges.Stiffenersmaybeaddedifneededtopreventbucklingoftheweb.

BoxgirdersareconstructedusingtwowebsasshowninFigure15–3b.

Open-websteeljoists(Figure15–4)andjoistgirdersareotherformsofbuilt-upsteel

members.Thesearelightweightopentrussesthatarestrongandeconomical.Theyarewidely

usedforsupportingfloorsandroofsofbuildings. Barjoists aresteeljoistswhosediagonal

membersconsistofsteelbars.Standard open-websteeljoist designationsincludeK,LH,and

DLHseries.Allaredesignedtosupportuniformloads.Kseriesareparallelchordjoiststhat

spanupto60ft(18.3m)withamaximumdepthof30in.(76cm).SeriesKusessteelwitha

yieldstrengthof50ksi(345MPa)forchordsandeither36ksi(248MPa)or50ksi(345MPa)

forwebs.SeriesLH(longspanjoists)andDLH(deeplongspanjoists)joistsareavailablewith

parallelchordsorwiththetopchordpitchedonewayortwoways(Figure15–5).Thestan-

dardpitchis 1

in./ft(1cm/m)toprovidedrainage.Longspananddeeplongspanjoistsare

normallycamberedtooffsetthedeflectionofthejoistduetoitsownweight.Theyusesteel

withayieldstrengthofeither36or50ksi(248or345MPa).SeriesLHjoistsspanupto96

ft(29.3m)withamaximumdepthof48in.(122cm).SeriesDLHjoistsspanupto144ft

(43.9m)withdepthsto72in.(183cm).

Joistgirders, SeriesG,aresimilartoopen-websteeljoistsexceptthattheyarede-

signedtosupportpanelpointloads.SeriesGgirdersusesteelwithayieldstrengthof36to

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