SINGLESKINAND DOUBLESKIN CONCRETEFILLED
TUBULAR STRUCTURES
ANALYSISANDDESIGN
MOHAMED ELCHALAKANI
UniversityofWesternAustralia,Perth,Australia
POURIA AYOUGH
UniversityofMalaya,KualaLumpur,Malaysia
BO YANG
ChongqingUniversity,Chongqing,China
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Acknowledgmentsvii
1.Introduction
1.1Introduction2
1.2AdvantagesofCFSTandCFDSTmembers2
1.3ErectionofCFSTandCFDSTcolumns5
1.4Applicationsofcompositemembers6
1.5Internationaldesignguidelines15 1.6Material15 References24
2.Experimentaltests
2.1Introduction30
2.2Cross-sectionalshapes33
2.3Experiments33
2.4Effectiveparameters39
2.5Failuremodes41
2.6Stiffenersincompositecolumns72
2.7Sizeeffects90
2.8Hollowratio100
2.9Effectsoftheconfinementfactor102
2.10Effectsofthematerialproperties105
2.11Loadeccentricity113
2.12Theroleoftheinnersteeltube119
2.13Materialimperfections125
2.14Effectsofpreloadandlong-termsustainedload153 References163
3.Analyticalmethods
3.1Introduction168
3.2Stress strainresponseofmaterials168
3.3Creepmodelforconcrete279
3.4CreepanalysisofCFSTcolumns284
3.5Aconstitutivemodelforcomputingthelateralstrainofconfinedconcrete298
3.6Axialandlateralstress strainresponseofCFSTcolumn305
3.7Ananalyticalaxialstress strainmodelforcircularCFSTcolumns308
3.8Pathdependentstress strainmodelforCFSTcolumns314
3.9Elastic-plasticmodelforthestress strainresponseofCFSTcolumns321
3.10Strengthenhancementinducedduringcoldforming332 References335
4.Numericalmethods
4.1Introduction343
4.2Numericalmodelingofconfinedconcrete343
4.3Investigatingthebehaviorofcompositemembersthrough numericalanalysis384 References533
5.Designrulesandstandards
5.1Limitationsofdesignregulationsonthestrengthofmaterialsandsection slenderness542
5.2Compressivedesignstrengthofcompositemembersbasedondesign guidelines546
5.3Momentdesignstrengthofcompositemembersbasedondesignguidelines577
5.4CFSTmembersundercombinedaxialloadingandbending609
5.5Strengthofcompositemembersbasedonresearchworks635
5.6Localbucklingofsteelplates678
5.7Furtherdiscussiononlocalbucklingofsteelplatesinrectangular CFSTcolumnsunderaxialcompression706
5.8CompressivestrengthofCFSTstubcolumnswithstiffeners732
5.9CompressivestrengthofCFSTstubcolumnswithlocalcorrosions776
5.10Straincompatibilitybetweenthesteeltubeandtheconcretecore785 References786
6.Futureresearch
6.1Introduction793
6.2Materialproperties795
6.3Geometricproperties798
6.4Nonuniformconfinement799
6.5Fireperformanceofcompositemembers801
6.6Stiffenedcompositemembers801
6.7Environmentallysustainablematerial805 References808 Index813
Acknowledgments
Theauthorswouldliketoacknowledgethepeoplewhohelpedtoprepare andreviewthemanuscript:Laila,Aya,YaseenandFaroukElchalakanifor reviewing Chapters1to6;ProfMostafaFahmiHassaneinforproviding materialsin Chapters1to6;DrMinhaoDongforprovingexperimental resultsin Chapter2;A/ProfSabrinaFawziaforreviewing Chapters5 and6;andDrShovonaKhursuforreviewing Chapters4and5
Theauthorsaregratefulfortheadviceoncompositestructures receivedfromeminentresearchersincivilengineeringfromdifferent partsoftheworld,includingProfSherifEl-TawilfromMichiganUniversity;ProfAlaaMorsyfromArabAcademyforScience,Technology,and MaritimeTransport;ProfMetwaliAbuHamadfromCairoUniversity; ProfSherifSafarandProfEzz-EldinSayedAhmedfromtheAmerican UniversityinCairo;ProfXiao-LingZhaofromUNSW/MonashUniversity;ProfGangadharaPrustyandProfSerkanSaydamfromUNSW;Prof NieShidongfromChongqingUniversity;DrShageaAlqawzai,ProfKang Chen,ProfLeShen,andDrMiaoDingfromChongqingUniversity; A/ProfNorHafizahRamliSulongandDrSabrinaFawziafromQUT; A/ProfZainahBintiIbrahimfromtheUniversityofMalaya;ProfAllan ManalofromUSQ;ProfHuaYang,ProfLanhuiGuo,andProfWeiZhou fromHarbinInstituteofTechnology;A/ProfMuhamadHadifromWollongongUniversity;DrMohamedAlifromtheUniversityofAdelaide; ProfEmadGad,ProfRiadhAl-Mahaidi,andProfJaySanjayanfrom SwinburneUniversity;ProfMostafaHassaneinfromTantaUniversity; ProfTong-BoShaofromSichuanUniversity;ProfDilumFernandoand DrChrisBecketfromtheUniversityofEdinburgh;ProfHongHao, DrThongPham,andDrWensuChenfromCurtinUniversity;ProfJingsi HufromHunanUniversity;ProfBrianUyandDrMichaelBambachfrom theUniversityofSydney;DrAfaqAhmedfromTaxilaUniversity;Prof SherifYehiafromAmericanUniversityinSharjah;andfinallyProfAli KarrechandDrMinhaoDongfromtheUniversityofWesternAustralia; andProfTianyuXiefromSouthChinaUniversityofTechnology.
Finally,wewishtothankourfamiliesfortheirsupportandunderstandingduringthemanyyearsthatwehavebeenundertakingresearch oncompositestructuresattheUniversityofWesternAustralia,theUniversityofMalaya,andChongqingUniversityduringthepreparationof thisbook.
PraisebetoAllah,theLordoftheworlds,theBeneficent,theMerciful, MasteroftheDayofRequital,TheedoweserveandTheedowebeseech forhelp.
Guideusontherightpath,thepathofthoseuponwhomThouhast bestowedfavours.Notthoseuponwhomwrathisbroughtdown,nor thosewhogoastray.
TheHolyQuran,SurahAl-Fatiha.
1.1Introduction
Theterm‘compositestructures’refertostructuresinwhichdifferent materialssuchastimber,steel,concrete,andmasonryareusedsimultaneouslyforconstruction.Themostcommontypeofcomposite constructionisthesimultaneoususeofsteelandconcretetoformsteelconcretecompositestructures.Steel-concretecompositestructuralmembersareknownaseconomicmembersandhavebeenusedtoconstruct variousstructuretypes.Itisaverywell-knownfactthatsteelmembersare susceptibletobuckling,whiletheirtensilestrengthisremarkable. Conversely,plainconcretememberscanwithstandalargemagnitudeof compressiveforce;however,theirtensilestrengthisdeficient.Therefore, thesimultaneoususeofsteelandconcreteallowsthestructuraldesigners totakeadvantageofsteelandconcreteandneutralizeeachmaterial’s drawbackbyusingtheothermaterial.Bytakingthisviewpoint,most structuralmemberssuchasslabs,columns,beams,andtrussescanbe constructedusingsteel-concretecompositemembers.Themainfocusof thecurrentbookistounderstandthestructuralbehaviorofconcrete-filled steeltubular(CFST)membersandconcrete-filleddoubleskinsteel tubular(CFDST)membersasoneofthemostrecentformsofcomposite members.Otherstructuralmembersarebeyondthescopeofthisbook.
1.2AdvantagesofCFSTandCFDSTmembers
Priortothedevelopmentofstructuraldesigncodesandregulations,a deepunderstandingofthebehaviorofstructuralmembersandknowing theperformanceandtheirfailuremechanismundertheconsidered loadingconditionarerequired.Usingtheavailablecodestodesign structuralmemberswithoutunderstandingtheirmaterialandstructural behaviorturnsmathematicalformulasintosetsofvagueconcepts. Therefore,theresultsoftheexperimentaltestsperformedonCFSTand CFDSTmembersarepresentedinthisbooktoshowtherealstructural behaviorofmembers.Certainly,experimentaltestsprovidevaluable informationregardingthebehaviorofstructuralmembers.However,for thoroughlyassessingtheinfluenceofdifferentparameterssuchas members’geometricandmaterialproperties,loadingconditions,initial geometricimperfections,andresidualstress,itisrequiredtofabricatea largenumberofspecimensintheadvancedstructuralengineeringlaboratories,whichcanbetime-consumingandexpensive.Recentimprovementsinthecapacitiesofcomputersinperformingcomplex mathematicalcalculations,aswellasthedevelopmentoffiniteelement (FE)softwarelikeABAQUSandANSYS,allowresearchersandstructural
engineerstoprofoundlyinvestigatethestructuralperformanceofmembersandstudytheirphysicalbehavior.Asaresult,thebehaviorofCFST andCFDSTmembersarestudiedthroughtheresultscapturedfromthe nonlinearFEanalysisinthisbook.AfterabasicunderstandingofCFST andCFDSTmembers’behavior,theavailableinternationaldesign regulationsfordesigningCFSTandCFDSTcolumns,beams,andbeamcolumnsareintroduced.Additionally,themostrecentdesignmodels developedbasedontheexperimentalandnumericalanalysisof compositemembersareincludedinthisbook.Designexamplesof compositemembersareutilizedwidelythroughoutthebook.
CFSTmembersconsistofahollowsteeltubefilledwiththeconcrete core,withorwithoutsteelreinforcementbars.Comparedwithhollow steelsectionsorthereinforcedconcrete(RC),thestructuralperformance ofCFSTmembers,suchastheirductility,compressive,bending,torsional strengths,fireresistance,andenergyabsorptioncapacities,areremarkablybetter.Besides,steeltubescanalsoactasconcreteformworkduring theconstructionprocesstoreducethetimeandcostofconstruction.These advantagesofCFSTmembersoverconventionalsteeltubeshaverecently attractedtheattentionofcivilengineersandhaveledtotheirwideusein recentstructures.TheideologybehindtheuseofCFSTmembersisthat theconcretecorecanavoidordelaythelocalbucklinginthesteeltubes. Besides,thebrittlebehavioroftheconcretematerialcanbehighly enhancedbytheconfinementeffectprovidedbythesteeltube. Fig.1.1 showsthecomparisonbetweendifferentsteeltubessuchassquare hollowsection(SHS),circularhollowsection(CHS),squareCFST,and circularCFST,basedontheiraxialstrengthundercompression.The compressivestrengthoftheconcreteusedinthesesteeltubeswasaround 40MPa.Besides,theschematicviewoftheaxialload-displacement
FIGURE1.1
FIGURE1.2 Comparisonbetweentheaxialcompressivebehaviorofsteelhollow sections,CFST,RC,andplainconcrete. Developmentsandadvancedapplicationsofconcrete-filled steeltubular(CFST)structures:members.JConstructSteelRes2014;100:211 228. https://doi.org/ 10.1016/j.jcsr.2014.04.016
responsesofCFST,RC,plainconcrete,andhollowsteelsectionispresentedin Fig.1.2.Itcanberecognizedfromthefiguresthatfillingthesteel tubewithconcretecouldhighlyenhancethecompressivecapacityofthe column.Inaddition,confiningtheconcretewiththesteeltubeimproved theresidualstrengthandductilityofthecolumn.
DespitetheadvantagesofCFSTmembers,theyalsohavesomedisadvantages,whichareasfollows:
1. Theoutersteelusuallytakesalargepartoftheexternalaxialloadas comparedtotheconcretecorebecauseofitshigherstiffnessunder compositeaction.
2. Theconcretecoreclosetotheneutralaxishasaninsignificant contributiontotheflexuralstrength.
3. Thecontributionoftheconcretecoreinenhancingthetorsional strengthisinsignificant.
4. Theinitialelasticdilationofconcreteunderaxialcompressionis relativelysmall,andthustheconfiningpressureprovidedbythe steeltubetoconcreteisrelativelylowduringtheelasticstage.
5. Theheavyself-weightoftheconcretecanlimittheperformanceof CFSTduetothestrength-to-weightratio.
Fromtheabovediscussion,itisquiteclearthatthecentralpartofthe concretecoreoftheCFSTcolumncaneffectivelybereplacedbyanother smallerhollowsteeltubewithsimilaraxial,flexural,andtorsional
1.3ErectionofCFSTandCFDSTcolumns
strength.ThisformofcolumnconstructionisknownastheCFDST columns.CFDSTmemberspossessseveraladvantagesoverthatofthe CFSTcolumn,whichcouldbesummarizedasfollows:
1. CFDSThavehigherflexuralandtorsionalstrengthascomparedto theCFSTmembers.Additionally,theirstrength-to-weightratiois improvedsignificantlybyreplacingthecentralconcretewithasteel tubeofamuchsmallercross-sectionalarea.Moreover,theinnertube expandslaterallyundercompressionloading,and,hencethe confiningpressureprovidedtotheconcretealsoincreases. Consequently,theinitialconfiningpressurebuildsupmorerapidly inCFDSTascomparedtoCFSTmemberssothattheirelastic strengthandstiffnessareenhanced.
2. CFDSTmemberscontainlessconcrete,whichcreatesamore sustainableenvironmentbyreducingtheembodiedenergylevels ofthemember.
3. Thecavityinsidetheinnertubeprovidesadryatmospherefor facilitiesorutilitiessuchaspowercables,telecommunicationlines, anddrainagepipes.Therefore,CFDSTmembersarechieflyuseful formaritimestructures.
1.3ErectionofCFSTandCFDSTcolumns
Duringtheconstruction,theinnertubeoftheCFDSTcolumniserected first.Thisisthenfollowedbytheerectionoftheoutertube.Afterthe erectionofbothtubes,theconcreteispouredinbetweenthem. Fig.1.3
FIGURE1.3 ErectionofCFDSTcolumns.(a)duringconstructionand(b)connection details. Developmentsandadvancedapplicationsofconcrete-filledsteeltubular(CFST)structures: members.JConstructSteelRes2014;100:211 228. https://doi.org/10.1016/j.jcsr.2014.04.016.
from[7]providestheerectionprocessofCFDSTcolumnsusedintransmissiontowers.Theplatesandboltsareusedtofixthepositionofthe tubes,whiletheflangesonbothendsofeachtubeareusedtoconnectit withitsextension.AsimilarprocedureisusedtoconstructCFSTcolumns, exceptthattheinnersteeltubeisnotinstalled.
Fabricationofhollowsteeltubescanbedonebyweldingsteelsheetsor usingthehot-rolledorcold-formedprocess.Dependingonthecrosssectionofthesteeltubes,differentshapesofcompositememberscanbe constructed,asshownin Fig.1.4
1.4Applicationsofcompositemembers
AppropriatestructuralperformanceofCFSTandCFDSTmembershas convincedstructuralengineerstousethemindifferenttypesofstructures likeindustrialstructures,structuralframes,electricitytransmittingpoles, andspatialconstructions.InChina,forexample,CFSTmembershave beenusedformorethan50years.In1996,structuraldesignersofsubway stationsinBeijingusedCFSTmembersastheprimarycolumns.Theuse ofCFSTmembersfortheconstructionofpowerplantbuildingsbacksto the1970s[7].Historically,theconceptof“doubleskin”composite constructionwasdevisedforuseinsubmergedtubetunnels[12].Agraph presentingthecross-sectionofthedoubleskincompositeconstructionis shownin Fig.1.5.Thiscross-sectionwasusedforthefirsttimeintheKobe MinatojimaSubmergedTunnelinJapan.Inthissection,someexamples fromtheuseofCFSTandCFDSTmembersinpracticearepresented.
Inthe1980s,andbyacceleratingthebuildinghigh-risestructures, structuralengineersdesignedandbuiltmanybuildingsusingCFST membersinBeijingandFujian,Chinatoreducethecolumns’size[9].
CFSTmembersaretypicallyservedasthecolumnsofcompositeframe systemsforbearingcompressiveloads,andtheyaregenerallyconnected tosteelorRCbeams.Toimprovethelateralresistanceofhigh-rise buildings,CFSTcompositeframestructuresaredesignedbyemploying RCcoretubesorsteelshearwallsasthelateralloadresistingsystem.The hybridstructuralsystemsconsistingofCFSTcolumnswiththecoretubes
FIGURE1.4 Differentshapesofcompositemembers.
FIGURE1.5 Exampleofsubmergedtub etunnelcrosssection. https://www. nipponsteel.com/result.html#/?ajaxUrl ¼%2F%2Fmf2apr01.marsflag.com%2Fnipponsteel__ all__customelement%2Fx_search.x &ct ¼&d ¼&doctype ¼all &htmlLang &imgsize ¼1 &page ¼ 1 &pagemax ¼10 &q ¼Development%20of%20sandwich-structure%20submerged%20tunnel% 20tube%20production%20method &sort ¼0 .
orshearwallsbenefitfromappropriatestiffnessandductility.Theperformedcyclictestonthebuildingsystemdepictedin Fig.1.6 from[8] indicatedthattheframe’sfirst-orderdampingratiosareintherangeof 0.03and0.035.
OneoftheearliestusesofCFSTmembersinhigh-risebuildingsisat SEGPlazainShenzhen,China,shownin Fig.1.7 from[7].Thebuilding has71floorswithaheightofalmost292m,inwhichcircularhollow sectionswithadiameterof1600mmandthesteelwallthicknessof28mm werefabricatedbyQ345steelandfilledwithC60concrete.Inthisproject, thesteelsectionsofthecolumnsweretransferredtothesite.Theshipped steelpartswereinthelengthsofthreestories.Aftertheinstallationof hollowsteelsections,steelI-beamswereconnectedtocolumnsusing bolts.Later,setsofcolumn-beamweretransferredtotheirexactlocation. Atthesametime,thedeckfloorswerefabricated.Theuseofthisstrategy allowedengineerstoconstructtwo-and-a-halffloorseachweek.Thefast constructionprocessofthisprojectprovestheefficiencyofcomposite structures.ComparisonofresultsshowedthattheuseofCFSTcolumns enabledstructuraldesignersofthisprojectreducetherequiredsteel materialandpreventtheuseofverythicksteelplates.Ifhollowsteel sectionswereused,therequiredsteelmaterialwouldbetwiceasmuchas thatusedforthefabricatedCFSTcolumns.TheSEGPlazaisthefirst super-high-risebuildinginChinainwhichcircularCFSTmemberswere used[13].
FIGURE1.6 Schematicviewofacompositestructuralsystemforhigh-risebuildings. Developmentsandadvancedapplicationsofconcrete-filledsteeltubular(CFST)structures:members.J ConstructSteelRes2004;100:211 228. https://doi.org/10.1016/j.jcsr.2014.04.016
Despitethebetterconfinementeffectprovidedbycircularsteeltubes andtheiraestheticproperties,theeaseoffabricationofbeam-to-column connectionsinrectangularcompositecolumnshasmadethempopularin compositeframes.RuifengInternationalCommercialBuildinginHangzhou,China,isshownin Fig.1.8 reproducedfrom[7]and[61],inwhich squareCFSTmemberswereusedascolumns.Theprojectconsistedoftwo towers.Thewestonehas24floorswithaheightof84.3m,andtheeast onehas15floorswithaheightof55.5m.ThecombinationofCFST compositeframesandthelateralresistancesystemofRCshearwallshas beenusedinthishybridstructuralsysteminwhichtheCFSTcolumns haveadepthof600mmandthesteelplatethicknessrangingfrom28to 16mm.
TheCantonTowerinGuangzhou,China,isamultipurposeobservationtowerthatconsistsofaspacelatticecompositeframetwistingaround anRCcore,asshownin Fig.1.9.Themainbodyofthestructurehasa 454mheight,andtheoverallheightofthetoweris600m.Twenty-four inclinedCFSTmembershavebeenemployedfortheconstructionof thistower.Themaximumdiameterofthesteeltubeis2000mm,andthe maximumwallthicknessofthetubeis50mm.
FIGURE1.7 SEGplazainShenzhen,China. Developmentsandadvancedapplicationsof concrete-filledsteeltubular(CFST)structures:members.JConstructSteelRes2004;100: 211 228. https://doi.org/10.1016/j.jcsr.2014.04.016.
Themassivecompressiveforcesinhigh-risestructurescanleadtoa largerequiredcolumncross-section.Themegacompositecolumncanbe usedtodealwiththeheavyaxialload,asshownin Fig.1.10 from[7].The crosssectionofthecolumnissplitintovariouschampersusinginternal webs.Theapplicationofinternalweb,longitudinalstiffeners,andreinforcingtiebarsimprovesthestabilityofsteelplates.Puringconcreteis performedusingventholesandmanholes.Ifthemember’scross-section islarge,itmaybenecessarytouseshearconnectorstoguaranteethe appropriateloadtransferbetweensteelandconcrete.Z15TowerinBeijing,China,withaheightof528m,hasbeenconstructedusingmega CFSTcolumns.
Theadvantagesofcompositememberscanbeexploitedinvariouskinds ofbridges,i.e.,archbridges,suspensionbridges,cable-stayedbridges,and trussbridges.Theycanbeusedfortheconstructionofpiers,towers,arches, aswellasthedecksystemofbridges.Differentbridgestructuresinwhich compositemembersareusedareshownin Fig.1.11 from[7].
FIGURE1.8 RuifengInternationalCommercialBuildinginHangzhou,China. Developmentsandadvancedapplicationsofconcrete-filledsteeltubular(CFST)structures:members.J ConstructSteelRes2004;100:211 228. https://doi.org/10.1016/j.jcsr.2014.04.016.
TheWangchangEastRiverBridgewithamainspanof2misthefirst archbridgeinChina,whereCFSTmemberswereused,asshownin Fig.1.12 reproducedfrom[7].Thecentralarchhasadumbbellshape cross-sectionwithatotaldepthof2m.C30concretewasusedforfilling thehollowsteelsectionsofbothtopandbottomchordswithadiameterof 800mmandawallthicknessof10mm.Asuperiorbenefitofadopting CFSTmembersinarchbridgesisthatthehollowsteeltubesactasthe permanentframeworkfortheconcrete,whichcanremarkablydecrease thetimeandcostofconstruction.Additionally,theinherentstabilityof thearchtubularstructureeliminatestheneedforatemporarybridgeto installthecompositearch.Theerectionofthecompositearchbridgecan bedoneusingrelativelysimpleconstructiontechnologyduetothelow
FIGURE1.9 Cantontower. GuangzhouTower.2009. https://commons.wikimedia.org/wiki/ File:Guangzhou_Tower2009.jpg
FIGURE1.10 MegaCFSTcolumncrosssection. Developmentsandadvancedapplicationsof concrete-filledsteeltubular(CFST)structures:members.JConstructSteelRes2014;100:211 228. https://doi.org/10.1016/j.jcsr.2014.04.016
FIGURE1.11 Applicationsofcompositemembersinbridges. Developmentsandadvanced applicationsofconcrete-filledsteeltubular(CFST)structures:members.JConstructSteelRes2014; 100:211 228. https://doi.org/10.1016/j.jcsr.2014.04.016
FIGURE1.12 WangchangEastRiverBridge,China. Developmentsandadvancedapplicationsofconcrete-filledsteeltubular(CFST)structures:members.JConstructSteelRes2014;100: 211 228. https://doi.org/10.1016/j.jcsr.2014.04.016.
weightofthehollowsteeltubes.Cantileverlaunchingtechniquesand horizontalorvertical“swing”techniquesarethemosttypicaltechniques forconstructingcompositearchbridges.
Anotherapplicationofcompositemembersisinsubwaystations. Columnsinsubwaystationsaregenerallysubjectedtosignificant
compressiveloads,anddesigningthemusinghollowsteelsectionsorRC membersmayleadtolargecross-sections.Therefore,structuralengineers oftheQianmensubwaystationinBeijing,Japan,employedcircularCFST columnsintheirdesign.Similarly,lines2and9ofthesubwaystationin Tianjin,China,havebeenconstructedusingcircularCFSTcolumns,as shownin Fig.1.13 reproducedfrom[7].
Compositememberscanalsobeemployedinindustrialbuildings.The useofcircularCFSTcolumnsinapowerplantworkshopisshownin Fig.1.14 from[7].Comparedtohollowsteelcolumns,theuseofCFST columnsinthisprojecthalvedtheconsumptionofsteelmaterials[7].
Compositememberscanbeutilizedintheconstructionofelectricity transmissionpylons.Thelong-spantransmissiontowerinZhoushan, China,withaheightof370m,isthebiggestelectricitytowersglobally,as shownin Fig.1.15 from[7].Fortheconstructionofthistower,atubular latticewithfourCFSTcolumnswithadiameterof2000mmhasbeen used.Recently,CFDSTmembershavebeenusedintheconstructionof electricalnetworkinfrastructures,asshownin Fig.1.16 from[7].
FIGURE1.13 Applicationofcompositemembersinsubwaystations. Developmentsand advancedapplicationsofconcrete-filledsteeltubular(CFST)structures:members.JConstructSteel Res2014;100:211 228. https://doi.org/10.1016/j.jcsr.2014.04.016
FIGURE1.14 Applicationofcompositemembersinapowerplantworkshop. Developmentsandadvancedapplicationsofconcrete-filledsteeltubular(CFST)structures:members.J ConstructSteelRes2014;100:211 228. https://doi.org/10.1016/j.jcsr.2014.04.016
FIGURE1.15 Zhoushanelectricitytransmissiontower. Developmentsandadvancedapplicationsofconcrete-filledsteeltubular(CFST)structures:members.JConstructSteelRes2014;100: 211 228. https://doi.org/10.1016/j.jcsr.2014.04.016.
FIGURE1.16 ApplicationofCFDSTcolumnsintheelectricitytransmissiontower. Developmentsandadvancedapplicationsofconcrete-filledsteeltubular(CFST)structures:members.J ConstructSteelRes2014;100:211 228. https://doi.org/10.1016/j.jcsr.2014.04.016
1.5Internationaldesignguidelines
Differentwell-knowninternationaldesignregulationslikeAmerican steeldesigncodeAISC360-16[1],BritishbridgecodeBS5400[11], JapanesecodeAIJ[2],ChinesecodeDBJ13-51[3],AustraliancodeAS5100 [10],andEuropeancodeEC4[5]supporttheuseofCFSTstructures. However,nodesigncodeshavebeendevelopedtocoverthedesignof CFDSTmembers.Therefore,structuralengineerstypicallyhavetomodify themodelsrecommendedforCFSTmemberstodesignCFDSTmembers. Forthesakeofsimplicity,thecodesarenamed“AISC360-16”,“BS5400,” “DBJ13-51,”“AS5100,”and“EC4”inthisbook.
1.6Material
Asdiscussedabove,aCFSTmemberconsistsofahollowsteelsection withaninfilledconcretecore.Thesteeltube’sfabricationcanbedone
TABLE1.1 Typesofconcreteusedforcompositecolumns.
Concrete NotationReferences
Polymerconcrete PC [47,48]
NormalstrengthconcreteNSC[20,24,30,32,41 44,52,62,63]
HighstrengthconcreteHSC[15,20,25,29 32,34,39 42,44 46,51 53,62]
Ultra-high-strength concrete UHSC[29,30,40 42,49]
Rubberizedconcrete RuC[17 19,22,23,33,59]
Self-compactingconcreteSCC[14,21,26 29,35,36,50]
Seawaterandseasand concrete SWSSC[37]
Grout GR [38] 1.Introduction
usingweldingsteelplates,hot-rolling,orcoldformingsteelmaterial.The steeltubecanbefabricatedusingmildcarbonsteel,highstrengthsteel, stainlesssteel,high-performancefire-resistantsteel,andaluminum.The employedconcretematerialcanbeanormalstrengthconcrete(NC),high strengthconcrete(HSC),ultra-high-strengthconcrete(UHSC),orselfconsolidatingconcrete(SCC).Otherconcretetypes,suchaspolymer concrete(PC)orevenrubberizedconcrete(RuC),canalsobeapplied.
Table1.1 summarizesthemostrecentexperimentalandnumericalstudies conductedoncompositecolumnsusingdifferenttypesofconcrete material.However,designregulationsprovidesomelimitationsforusing steelandconcretematerial,whichareaddressedinthissection.
1.6.1Steel
1.6.1.1AS5100part6
AS5100onlycoversstructuresbuiltbysteelmaterial,havingayield strengthoflessthan450MPa.Besides,thesteelelementsshouldhavea thicknessofatleast3mm.Symmetricalsteelsectionshavingayield strengthofnotmorethan350MPamustbeemployed.Besides,the slendernessofthesteelplatemustsatisfytheyieldslendernesslimit.
1.6.1.2BS5400part5
BS5400allowstheuseofcircularandrectangularhollowsteelsections forthefabricationofcompositemembers.Thehollowsteelsectionsmust besymmetrical,andsteelgradesofS275orS355shallbeusedinaccordancewithstandardsEN10025[4]orEN10210[16].Also,theslenderness ofthesteelplatemustsatisfytheyieldslendernesslimit.
1.6.1.3DBJ13-51
AccordingtoDBG13-51,thesteelmaterialusedforCFSTmembers shallbeinaccordancewiththesteeldesigncodeGB50017[54].Foursteel gradesofQ235,Q345,Q390,andQ420canbeemployedbasedonthe Chinesecode.
1.6.1.4Eurocode4
EC4referstoclauses3.1and3.2ofEurocode3Part1.1[6]forthesteel materiallimitation.BasedonEC4,themaximumsteelyieldstressmustbe lessthan460MPa.
1.6.1.5AISC360-16
AS360-16allowstheuseofcircularandrectangularhollowsteelsectionsforthefabricationofcompositemembers.Thesteelyieldstrength forthefabricationofhollowsteelsectionsmustbelimitedto525MPa. Theminimumallowableyieldstressfy andtensilestrengthfu defined bydesigncodesarelistedin Table1.2 forsteelplates[4,17,55,58], Table1.3 forhot-rolledhollowsteelsections[16],and Table1.4 forcold-rolledhollow steelsections[56,59,61].Itcanberecognizedfromtablesthatfy ranging from200to460MPaandfu rangingfrom300to720MPa.Thetensile strength-to-yieldstressfu .fy ratioisintherangeof1.11and1.96.
1.6.2Concrete
1.6.2.1AS5100
AccordingtoAS5100,concretehavingnormalstrengthanddensity, basedontherequirementsofAS5100Part5,mustbeused,andthesizeof theaggregateshouldbelimitedto20mm.Inaddition,ifsteelreinforcementbarsarerequired,theymustmeetAS5100Part5.Thecharacteristic compressivecylinderstrengthat28daysrangesfrom25to65MPa. Besides,thesaturatedsurface-drydensityoftheconcreteshouldbeinthe rangeof2100 2800/m3.AccordingtoAS5100,themodulusofelasticity oftheconcreteisgovernedby:
wheretheterm r denotesthedensityoftheconcreteand fcm istheaverage amountofconcretecompressivestrengthattherelevantage.
