FrameConstructionSteelFrames Bracing TimberFrames

ComparrisonofPortalFramingSystems FlyBracing TheAdvantagesandDisadvantagesofaTimberFrame

ComparisonofTrussvs.PortalFrames RoofBracing

PortalframesAdvantagesDisadvantages Haunching

Roofpitch StiffeningPlates

PurlinsandGirts

Entrances

Considerationforstructuresduringconstruction

Connections Conclusion References

INTRODUCTIONTOFRAMESWhendesigningtheframeforboththewarehouseandshowroomitisimportanttoconsiderthestrengthoftheframeagainstDeadLoads(theloadofthestructure)andLiveLoads(loadsimposedonthebuildingsuchaswind).Theseconsiderationsmusttakeintoaccountthefundamentalsofcostandaesthetics(moresointheshowroom).

STEELFRAMES Top

Theuseofsteelinaframehassomeclearadvantagesanddisadvantagesasamaterialtoworkwith.Oneofsteelsgreatestadvantagesisthatsteelhasa'qualitycontrol',meaningthesteelyoureceiveisofacertainstandardthathaslittlevariables,unlikeapeaceofwoodwhichhasimpuritiessuchasknotsandcracksinitwhichwillweakenit.Andunlikewoodsteelhasalowcreeplevel.Steelsspanningcapacityisalsoimpressive,asisthespeedthatasteelconstructioncanbeerected(accordingtoBHP,about20%fasterthanmostotherconstructions),asmemberscanbeprefabricatedoffsiteandthenconnectedquicklyonsite,allowingconstructiontobelargelyunhinderedbyweather.Steelalsohassomedisadvantages.Structurally,steelwillfailwhenengulfedinafiremuchfasterthanifitwasasolidwoodenframe.Thecostofasteelframeisalsoincreasedduetofactorssuchasthenecessityofskilledlabortoerectthestructure,corrosiontreatmentofmetalandahighdegreeofeffortneededtochangeerrors.Environmentallysteelhasahighembodiedenergyandisminedandprocessedwithadetrimentaleffecttotheenvironment,howeversteelisrecyclableasstructuresarelargelyboltedtogetherenablingthemtobesimplyunboltedandputbacktogetherinanother

location.

ComparrisonofPortalFramingSystems Top

ComparisonofTrussvs.PortalFrames Top

PortalframesAdvantagesDisadvantages Top

Roofpitch Top

Theroofpitchofaportalframeshouldbekepttoaminimumtoreducethehorizontalforcesactingonthecolumnsofthestructure.Asthepitchoftheroofisincreased,sotoodothehorizontalforcesactingonthecolumnswhicharedesignedtoonlywithstandverticalforcesduetothelawofvectors(seefigure1).

.Figure1

PurlinsandGirts Top

PurlinsandgirtscomeinZandCsectionsandareusedtoattachabuildingscladdingtoitsframe.Theymakeupabout24%ofthetotalsteelusedintheconstruction.Itisforthis

reasonthataminimalnumberofpurlinsandgirtsshouldbeusedinordertosavemoney.Formostindustrialbuildings,purlinswhichareabout200mmdeepappeartobeaneconomicallysufficientoption.InmostcasestheyareheldintoplacewithM12bolts.Tocreateacontinuousspan,ZsectionscanbeoverlappedandconnectedwhereasCsectionneedtobeconnectedatasupport.(seefigures2and3).

.Figure2:TheconnectionbetweenZandCsections,andarafter[takenfromZaragoza,pg.

29].

.Figure3.

Entrances Top

Fromresearchingportalframedbuildingsonsite,largedoorwaysof6metersorlessand

highenoughtoenabletruckentrywereclosedoffwithrollerdoorsattachedstraightontotheframework.Therewasnochangeinsizeforthecolumnswhichtherollerdoorswhereattachedto(seefigure4).Asfordoorwaysforpeoplethesewheresimplydoorframesattachedstraightontothecladding.Whenlocatingdoorsitisimportanttorememberthattheremustbeamaximumof20mtothenearestexitwithinabuilding,duetorestrictionssetbytheBCA.

.Figure4:Showsarollerdoorconnecteddirectlytoacolumnoftheportalframe.

Considerationforstructuresduringconstruction Top

Whenerectingaframeitisimportanttoconsiderthedeflectionrateofabuildingunderitsownweight,orthebuildingsdeadload.Thereforewhenerectingthestructuretheframeshouldbepositionedsothatitopposesthedeflectionforces.

BRACING Top

Bracingisanessentialpartofeachandeverystructurebeingerectedinalmosteverycountryintheworldtoday.Itsfunctionisessentiallytoincreasethestructuresstrengthinordertopreventitfromfallingdownwhilsthavingaloadsuchaswind,rainorsnowapplied,aswellasbeingabletosupportitsdeadload.Belowisalistofbracingtypeswhichwefoundwereinuseinthewarehousesvisitedwhilstundergoingvarioussitevisits.

FLYBRACING Top

Flybracingisanessentialelementineverylongspanportalframewarehousedesign,asitnotonlypreventsthepurlinsfromtwistingandoverturning,butitalsolengthenstheinfluenceoftherafterbyincreasingtheroofsstrength,whichisespeciallyusefulforthebuilderscladdingtheroof.ThephotographicdetailsbelowweretakenataconstructionsiteinTorquay,andhighlightwhereflybracingisusedinwarehousedesign.

.Examplesofflybracing.

.Theforcesopposedbyflybracing.

Flybracingisalsosometimesusedonthecolumnsandgirtsofaportalframetoalsopreventtheseelementsfromtwisting,howeverflybracingdoesaddcosttothebuildingandthereforeshouldonlybeusedwhereneeded.

.Flybracingbeingusedoncolumns.

ROOFBRACING Top

Crossedroofbracingisanothertypeofbracingwhichisessentialtotheerectionoflongspandesign.Itsfunctionistopreventtherafters/beamsofthestructurefrommovingapartfromoneanotherduetoawindloadbybeingplacedundereithertensionorcompression.Thefollowingdiagramillustrateshow

Thefollowingphotographsillustratehowroofbracingisincorporatedintothestructureandhowitisattachedtotherafters/beams.

.Anexampleofroofbracing.

.Theconnectionbetweenrafterandroofbracing.

HAUNCHING Top

Forspansofover20metres,extrabracingisrequiredtokeepthesteelsubstructurefromcollapsinginonitself.Thisbracingisknownas'haunching'andisusuallymadeofacuttoshapeuniversal'I'beamwhichfitsintothecornermadebythestanchionandtherafters.Ahaunch'sdepthisusuallyaboutthesameasthedepthoftherafter,andintermsoflength,isusuallyintheorderofabout1015%ofthespanoftherafter.Ahaunchcanalsosignificantlylowerthecostofthesteelrequired,forexample,aportalframesectionmay

costaround$950usinga450UB67rafterhoweverusinga310UB67theraftermaycostonlyasmuchas$800assumingthatahaunchisbeingused.

.AnexampleofhaunchingataBunning'swarehouse.

Anotherlocationwherehaunchingcanbefoundinlongspanconstructionisattheapexofthestructure.Again,thehaunch'sdepthisusuallyaboutthesameasthedepthoftherafter,howeverintermsoflength,theapexhaunchingisclosertobetween3040%ofthespanoftherafter.

.ApexhaunchingatawarehouseinTorquay.Thisphotoalsoshowstheapexconnection

betweenthetworafters.

STIFFENINGPLATES Top

Stiffeningplatesareanothertypeofbracingusedtoprevent'UniversalBeams'frombendingandtwisting.Thefollowingphotographshowsastiffeningplateinuse

CONNECTIONSThewayinwhichanelementisconnectedtoanotherelementwillultimatelyaffecthowtheelementswillperform,thereforemuchattentionshouldalwaysbepaidtowhichconnectiontypeischosenforeachsituation.Theconnectiontypeusedisentirelydependentonthestructuralsystemchosen,whetheritbecolumnandtruss,threepinnedportaltrussortheportalframesystem.Belowisalistofthethreedifferentsystems,andtheadvantagesanddisadvantageseachsystemhas.Beforeanyconsiderationcanbegiventotheconnectionsbeingused,aconstructionsystemmustfirstbechosen.

COLUMNANDTRUSSThecolumnandtrusssystemwasdevelopedintheearlydaysofwarehousedesign,whenlabourwasrelativelycheapwhencomparedthecostsassociatedwithitnow.Duetothelabourintensiveprocessofprefabricationandthecostsassociatedwithproductionoftrusses,thissystemhasbeennearforgottenaboutandhasmadewayforother,lesslabourintensivesystems.

.AColumnandTrusssystem[takenfromZaragoza,pg.25].

AdvantagesIntheearlydaysofwarehousedesign,labourwasrelativelycheapcomparedtonow,sotheprocessofprefabricationwasrelativelyinexpensive,meaningthatthissystemwasreasonablyeconomicalandadoptable,howevernow,duetorisinglabourcosts,

prefabricationhasbecomealotmoreexpensive.Lesssteelisusedthanboththeportalframesystemandthethreepinnedportaltrusssystem.

DisadvantagesCostlyprefabricatedtrussesareneeded.Cannotspanoverlargedistances.Difficulttoerect

VerdictThistypeofsystemwasnotplausibleforourtypeofconstruction,duetothelargespanneededandtheexcessivelabourcostwhichcomeswithemployingthistypeofsystem,therefore,wedidnotchoosetoemploythecolumnandtrusssystem.

THREEPINNEDPORTALTRUSS

Forspansofbetween4570metres,thethreepinnedportaltrusssystemisoneworthconsidering,howeverdependingontheconnectionmethodusedbetweentrusselements,andhowmuchweldingisusedtoconnecttheseelementsinsteadofthetraditionalrivets,willaffecthoweconomicalthesystemis.

.AThreePinnedPortalTrusssystem[takenfromZaragoza,pg.30].

AdvantagesForspansofbetween4570metres,thethreepinnedportaltrusssystemprovidesacheapermoreeconomicalalternativetoemployingmassivelywideuniversalbeams,whichwouldneedtobeusedshouldtheportalframesystembeemployed.

DisadvantagesForspansoflessthan45metres,thecostandamountoflabourthatneedstobeusedinthecreationofathreepinnedportaltrusssystemfaroutweighsthematerialandlabourcostsassociatedwithaportalframesystem,thereforedeemingittobeinefficient.

VerdictDuetothesub45metrespanofourwarehousedesign,thethreepinnedportaltrusssystemwasdeemedtobeuneconomicalduetotheexcessivelabourcoststhatthissystemrequires,especiallyforaspanassmallasours.

PORTALFRAME

Theportalframesystemiswidelyconsideredthemosteconomicalsolutiontoawarehousedesignofspanbetween1545metres.Eventhoughboththecolumnandtrusssystemandthethreepinnedportaltrusssystemrequirelesssteeltobuild,duetothefactthatbothof

thesesystemsaremorelabourintensiveandarehardertoerectmeansthatoverall,theportalframesystemisthemosteconomicalsystemtouseovera1545metrespan.

.APortalFramesystem[takenfromZaragoza,pg.25].

AdvantagesThelabourcostsassociatedwithbuildingthistypeofsystemaresignificantlylessthanboththecolumnandtrusssystemandthethreepinnedportaltrusssystem.Theerectionoftheportalframesystemiseasierthanboththecolumnandtrusssystemandthethreepinnedportaltrusssystem.Inmanyinstances,lessbracingisneededthanwhatwouldberequiredhadeitheroftheothertwosystemsbeenemployed.

DisadvantagesMoresteelisneededtobuildthistypeofsystem

VerdictFora1545metrespan,thistypeofsystemwasdeemedtobethemostsuitable,thuswaschosenbyusasthemostappropriatesystemforwhatweneed.

Oncechosen,theconnectiontobeusedcanthenbeselected.

STANCHIONSLAB/FOOTINGJOINT(ofaportalframe)

PINJOINTS

UsePinJointsareanincreasinglyraretypeofconnectionbetweenstanchionandslab/footing.Theyarenotcommonlyusednowadaysduetotheirinabilitytotransferbendingmomentsasefficientlyasrigidbases,astheymusttransferthebendingmomentverticallythroughtheground,notthefooting.Theyarehoweverefficientateliminatingrotationalforces(howeverrigidjointsarealsocapableofdoingthis).

.Arigidjointseenonsite

AdvantagesAresuitableforpoorfoundations(suchastheClassMsoilonwhichoursiteisbuilt).Aregoodateliminatingrotationalforces.Requireslessconcrete,thereforearemorecostefficientoverlongspans.

DisadvantagesAremorecostlyoversmallerspansduetoincreasedsteelusage.Doesnottransferbendingmomentsthroughfootings.Increasedbracing,comparedtoarigidjoint,maybenecessary.

RIGIDJOINTS

UseRigidJointsarethemorecommonlyusedconnectiontypebetweenstanchionandslab/footing,duethefactthatcancarrybendingmomentsandalsoaxialloads.Indoingso,theyareabletosignificantlyreducetheamountofmovementintheframe,especiallyaroundthejointbetweenstanchionandslab/footingbytransferringtheloadsdirectlytothefootings.Thisalsomeansthattheframecanbelighter,leadingtoareducedcostinframingmaterials.Concretecostshoweverareincreased,duetothelargeramountofconcreteneededtohousetheextrabolts(4areneeded,comparedto2or3forapinjoint).

.TwoexamplesofaRigidJoint

AdvantagesLighterframecanbeused,leadingtoareductioninframingcosts.Aremorecostefficientforsmallerspannedareas.

DisadvantagesIncreasedconcretecostduetoextrahousingneededforextrabolts(thefurtherthebolts

arefromthestanchion,thestrongerthejointwillbe).Arelesssuitableforpoorfoundations.Rigidbasehaslittleadvantageoverlargespans,likethatwhichwearedealingwith.

KNEEJOINT(ofaportalframe)

Duetothelargespanofourwarehousedesignonlytwotypesofjointswereplausibleforthissituation,onebeingaweldedjointandtheotherbeingaboltedjoint.Haunchingwasnecessityforourwarehousedesignduetothefactthatthespanbeingcoveredisover20m(forspansunder20m,haunchingmaynotbenecessary).

WELDEDJOINT

Examplesofaweldedjoint[takenfromZaragoza,pg.25].

AdvantagesRequirelessdetailingthanboltedjoints.Noconsiderationsneedtobemadetotensionedbolts.

DisadvantagesCanonlyspanadistanceofapproximately20metres.Notasmuchtensioning/adjustingofthejointcanbedoneonsiteasthatcanbedonebyaboltedjoint.

VerdictAsweldedjointsonlyhaveaspanningcapacityofapproximately20metres,wechosenottoemploythemasthejointofchoiceforboththekneejoint.

BOLTEDJOINT

Examplesofaboltedjoint[takenfromZaragoza,pg.25].

AdvantagesAssuminghaunchingisused,canspanadistanceofupto45metres.Jointscanbetightenedandadjustedonsitefarmoreeasilythanweldedjoints.

DisadvantagesAttentionmustbepaidtothedetailingofthejointswhentensionedboltshavebeenemployed.Ifshortcutsaremadebyattemptingtosimplifythejointsbyincreasingtheamountofworkdonebythefabricator,thenclearanceproblemsmayariseonsite.Ifajointhasbeenpoorlydetailedandcannotbetightened/tensionedonsite,thenseriousproblemsmayoccur.

VerdictDuetothefactthatthissortofjointcanbemoreeasilyadjustedandtightenedonsite,wechosetoemployboltedjointingatthekneejoint.

APEXJOINT(ofaportalframe)Onceagain,onlytwotypesofjointswereplausiblefortheapexjointofourstructure.Theyaretheweldedjointandtheboltedjoint.

WeldedJoint|BoltedJoint

CONNECTIONBETWEENTILTSLABANDRAFTER

Duetothefactthatwehaveincorporatedafirewallintoourwarehousedesignbyplacingatiltslabattheconnectingpointbetweenthewarehouseandtheshowroommeansthatwehadtodealwiththeissueofaconnectionbetweensomeoftheraftersandthetiltslab.Thiswasaddressedby,aftervisitingafewsites,boltingametal'shelf'intotheslabandultimatelyallowingtheraftertosituponit,asshowninthephotographbelow

.Aconnectionbetweenrafterandtiltslab

Whatthisalsomeantwasthattherewouldbeapurlinrunningparallelwiththetiltslab,thusthisalsoneededconnecting.Thistoowasaddressedbyconductingsitevisitsandobservingwhatthecommonpracticeis.Thesolutionwasasfollows

.Aconnectionbetweenpurlinandtiltslab

TheWebTrussThewebtrussisanothermethodofspaninglargedistancesandcoveringlargeunencumberedspaces.Intheconstructionofthewarehouseresearchedforthisprojectbuiltby"MecanoSheds"inQueenslandawebtrusswasemployedforpartofitsspace.Inconsultationwiththedeveloperwhobuiltthiswarehouseitwasfoundthatthisdecisionwasmadeonaneconomicbasis.Intheopinionofthedeveloperaprefabricatedtrusssystemmadeupofpreassembledcoldformedelementswasfarcheaperandlighterthanalargeuniversalbeam.Howeverthefactthatthetrusssystemwasonlyemployedforthepartofthewarehousethatspans20metressuggeststhatitisnotadequateforspanslongerthanthat.Forthesectionofthewarehousespanning30metresasystememployingcompositehotrolled'c'sectionswasused.Forthesereasonswehavedecidedtousethewebtrusssystemintheupperstoreyshowroom.

WarehouseinQueensland

CADmodeloftheframe

WarehouseReasearchPlan's Top

Design1

TIMBERFRAMES Top

Introduction

Timberframesarebestsuitedtostructureswithclearspansofbetween1530metres.Asastructuralmaterial,woodhasseveraladvantagesanddisadvantages,whicharediscussedinthetablebelow.TheuseofwoodinstructuresfallsintofourmaingroupsSolidlengthsofwoodwhichareusedasstructuralmembers'Boxbeams'aremadeupofplywoodorLVLandareusedtocreatestructuralmembersof

differentsizesandforms(seefigure6)withawidthrangingfromL/8toL/12where'L'isequaltothelengthoftheboxbeam.Thesetypesofmembershaveaveryhighstrengthtoweightratioandsothereforecanspangreatdistances.Aboxbeamalsohaslessvolumeinitthanasolidpeaceofwood,andsothereforecostsless.Structuresusing'boxbeams'arethemosteconomicalatspanninglargedistances(seefigures7and8).Glulamismadeupoflaminatedsheetsstucktogethertocreateathickmemberwhichismuchstrongerthanasolidpeaceofwood.ThesheetsofplywoodmustbestucktogetherusingTypeAbondsasstandardisedbythePlywoodAssociationofAustralia(PAA).Glulamhasthesameresistancetofireasasolidpeaceofwood.Trussframescanbemadeupofeithersolidtimber,'boxbeams',and/orGlulamplanks.Thetrussstructure,thoughmoreexpensive,cancomplementastructureaestheticallyandinsomecasessuchaswithsolidlengthsofwood,willincreaseitsspanningability.(seefigures9and10).

.Figure6.(takenfromhttp://oak.arch.utas.edu.au/research/portal.asp#introduction)

.Figure7(takenfromhttp://oak.arch.utas.edu.au/research/portal.asp#introduction)

.Figure8(takenfromhttp://oak.arch.utas.edu.au/research/portal.asp#introduction)

.Figure9(takenfromhttp://oak.arch.utas.edu.au/research/portal.asp#introduction)

.Figure10(takenfromhttp://oak.arch.utas.edu.au/research/portal.asp#introduction)

TheAdvantagesandDisadvantagesofaTimberFrame

.Figure11(takenfromhttp://oak.arch.utas.edu.au/research/portal.asp#introduction)

CONCLUSION Top

Warehouseconstruction

Forthewarehouseframe,wechosea'onewayrigidframe'.Thisframewaschosenbecauseitwascosteffective,inthatyouaresavingmoneybyhavingsimpleconnectionsonthebracedplanes.Thisframingtypewasalsochosenduetoitslargespanningability,creatingopenfloorspacewhichenablesthewarehousefloortoberearrangedinanyway.Thoughtheuseofa'twowayrigidframe'wouldalsogivealargeopenspanningability,thecostofhavingrigidconnectionsthroughouttheentirebuildingwouldhavebeenanunnecessaryexpense.Theuseofatwowaybracedframewasnotuseddespitethefactthatmoneywouldhavebeensavedonsimpleconnectionsthroughoutthebuilding.Heavierbeamsandmuchmorebracingwouldhavebeenneededwhichwouldhaveraisedthepriceoftheoverallstructure.A'woodenportalframe'wasnotchosenforfourreasonsFirstly,thefactwoodhasmuchmorearticulatedmovementandcreepthansteel.Secondly,thatwoodstructuresarepronetorotting,warping,andsplittingunlessmaintainedandtreated,addingcostsontothelifeofthebuildingthatmayexceedtheinitialcostmarginbetweensteelandtimberconstruction.Thirdly,thefactthatwooddoesnothaveashigha'qualitycontrol'inregardstoknotsandsplitsinthetimber,comparedtosteelwhichisconstantlyconsistentthoughoutthemember.Lastlythefactthatinafire,a'boxbeam'(themostcosteffectiveformofconstruction)willnotlastaslongassteelasitismadeupofthinmembersinaboxformation.Thememberssizesfortheportalframeselementswhereascertainedbyexaminingstructuresunderconstructionandalreadymadestructures,namelythoseat'Fagg'sMitre10inSouthGeelongand'BunningsWarehouse'inCorio.Fromtakingmeasurementsofthesebuildingsmembersandstudyingtheirplans(seebelow)wewereabletoestablisharoughunderstandingofthesizesneededtospanadistanceof40metres.Tosavemoney,thedimensionsofthebuildingwherereducedfrom40mx40mto30mx54m.Thischangeinwidthenabledustousesmallermembersspanasmallergap,thussavingmoneyonmaterials.Usingthesemeasurements,andwiththehelpofourtutor,wewereabletochosesmallermemberswhichwouldeffectivelyspanthe30metreclearance.Theheightofthewarehousewaslargelydecidedbytheheightofaforklift.Fromthiswewereabletodecidethatthebuildingshouldbe5500mmhighatitslowestpoint(thelongedges).Asforthepurlinsandgirts,Zsectionswherechosenfortheroofastheycanbeconnectedtoformacontinuesmembersavingmoneyandaddingstrength.ThegirtsaremadeofZsectionsbecausetheytoocanbemadeintocontinuesmembers.

.Figure12(takenfromP.J.O'ReillyandAssociates).

Figure13(takenfromP.J.O'ReillyandAssociates).

Figure14(takenfromP.J.O'ReillyandAssociates).

Figure14(takenfromP.J.O'ReillyandAssociates).

References Top

http://oak.arch.utas.edu.au/research/portal.asp#introductionwww.Ibstructures.co.uk/metspan.htmwww.rpi.eduwww.arch,usyd.edu.auBEMilnerHR,Thedesignandconstructionoftimberportalframes,ChisholmInstituteoftechnology,Melbourne,1988MainstoneRowlandJ,DevelopmentsinStructuralform,1steditionwithRIBAPublishingLtd1975,PenguinBooks,1983.Constructionandstructures2readerZaragoza,JosR,EconomicalStructuralSteelworkFourthEdition,AustralianInstituteofSteelConstruction,Sydney,1997