帮助团队成员认识到合作重要性

INTRODUCTIONConnectionsaredefinedasthesystemorassemblyusedtotieaprecastmembertothesupportingstructureortoanadjacentmemberwhilefixingsarethehardwarecomponentofconnections.Inthedesignofconnectionsstructuralredundancyisgenerallyeliminatedtominimiseforces.Therefore,itiscriticallyimportantthatloadpathsforforcesthroughthestructure,fromelementsthroughconnectionsdowntothefootingsandfoundationarecarefullyreviewed.Wherepossibleitisprudenttodesignastaticallydeterminatesystem,whichwillaccommo-datelong-term,incrementalvolume-changemovement.Considerationofconnectionbehaviourduringbotherectionandthelifeofthestructureareimportant.Practicalandeconomicalconnectiondesignmustconsiderthemanufactureoftheelementsandconstructiontechniques,aswellastheperformanceoftheconnec-tionsforbothserviceabilityandultimatelimitstates.Designoftheoverwhelmingmajorityofconnectionsisasimpleeverydayaffairbuttheprinciplessummarisedherearethebasisofallconnectiondesign.GENERALDESIGNCRITERIAConnectionsandfixingsmustmeetthefollowingcriteria.StructuralAdequacyDuctilityAccommodationforVolumeChangeDurabilityFireResistanceProductionSimplicityConstructionSimplicity.StructuralAdequacyAconnectionmustresisttheforcestowhichitwillbesubjectedduringitslifetime.Someoftheseforcesareapparent,forexamplethosecausedbydeadandlivegravityloads,wind,earthquake,andsoilorwaterpressure.Othersarenotsoobviousandarefrequentlyoverlooked.Thesearetheforcescausedbyrestraintofvolumechangesintheelements(seebelow)andforcesrequiredtomaintainstability.Instabilitycanbecausedbyeccentricloading,aswellaslateralloadsfromwindandearthquake.Measurestakentoresistinstabilitymayaggravatetheforcescausedbyvolumechanges,andviceversa.Theconnectionresistancecanbecategorisedbythetypesofforcetowhichitissubjected.Theseinclude:CompressionTensionFlexureShearTorsion.Manyconnectionswillhaveahighdegreeofresistancetoonetypeofforce,butlittleornoresistancetoanother.Forexample,aconnectionmayhaveahighshearcapacityandlittleornomomentcapacity.Foragiventypeofconnectionitmaybeunnecessary,orevenundesirabletoprovideahighcapabilitytoresistcertaintypesofforces.DuctilityForthepurposeofdesignofconnections,‘ductility’isdefinedastheabilitytoaccommodatelargedeformationswithoutfailure.Instructuralmaterials,ductilityismeasuredbytheamountofdeformationthatoccursbetweenfirstyieldandultimatefailure.Ductilityinbuildingframesisusuallyassociatedwithmomentresistance(rotationalductility)andinthecaseofprecaststructuresmayhaveamajorimpactonconnectiondesign.Flexuralordirecttensionisnormallyresistedbysteelcomponents,eitherreinforcingbarsorstructuralsteelsections.Connectionsareproportionedsothatfirstyieldoccursinthissteelcomponent,andfinalfailuremayARTICLESFROMNUMBERS23,24,25•APRIL,SEPTEMBER,DECEMBER2000NATIONALPRECASTCONCRETEASSOCIATIONAUSTRALIAWEBADDRESS:•EMAIL:[e-mail]ixingsSimplebearingconnectionsareeffectiveandeconomicalCorbelanddowel(load-carryingfixing)Tie-backfixing(lateralrestraint)Claddingpanels–themostcommonfixingmethodformulti-storeybuildingsiselegantandeconomicalFloorstarterbarsGrouteddowelbarThemostefficientwaytoutiliseprecastcladdingistomakeitloadbearing,theconnectiondetailsarestraightforwardbefromruptureofthesteel,crushingoftheconcrete,orafailureoftheconnectionofthesteeltotheconcrete.AccommodationforVolumeChangeThecombinedeffectsofshrinkage,creepandtemperaturedifferencescancauseseverestressesonprecastconcreteelementsandtheirsupportsiftheendconnectionsrestrainmovement.Aconnectionshouldeitherbeabletoaccom-modatethesestrainsorbestrongenoughtowithstandtheinducedforces,oramixtureofthetwo.(Thesestressesmustbeconsideredinthedesign,butitisusuallyfarbetteriftheconnectionwillallowsomemovementtotakeplace.Thiscanbeachievedbyslottedholesorslidingbearings).Build-upofforceduetotheseeffectstakestimeanditcantakemanyyearsbeforethefulleffectsarefelt.Mostofthesevereproblemsthathavebeencausedbyrestraintofvolumechangemovementshaveappearedwhenrelativelylongelementssuchasfloordeckunitshavebeenweldedtothesupportsatbothends,egthecollapseofroofelementsofaschoolbuildinginAntiochafter20years.Whensuchelementsareweldedonlyatthetop,experiencehasshownthatvolumechangesareadequatelyaccommodated.Onrelativelyshort,heavilyloadedelementssuchasbeams,anunyieldingtopconnectionmayattractnegativemomentwhichisdifficulttodesignfor.Prestressedelementsrarelyexhibitcrackingatlocationsfurtherfromtheendsthanthetransferlengthofthestrand.DurabilityAconnectionshouldbedurablefortheenvironmentinwhichitisplaced.(Whenexposedtoweather,orusedinacorrosiveatmosphere,steelelementsshouldbeadequatelycoveredbyconcrete,behot-dippedgalvanisedorbeofstainlesssteel.Reinforcedelementsshouldhaveadequatecoverofqualityconcrete.)Inmarineenvironmentsstainlesssteelmayberequiredforparticularfixings.Dissimilarmetalsshouldnotbedirectlycoupled.FireResistanceManyprecastconcreteconnectionsarenotvulnerabletotheeffectsoffireandrequirenospecialtreatment.Forexample,thebearingbetweenslabsorstemmedunitsandbeamsdonotgenerallyrequirespecialfireprotection.Iftheslabsorteebeamsres