土木工程專業(yè)英語(yǔ) 課件 5.1 Steel Connections

5.1SteelConnectionsClassificationofConnectionsTypeofconnectingmediumusedBoltedconnectionsWeldedconnectionsBolted-weldedconnectionsRivetedconnectionsTypeofinternalforcestheconnectionstransmit

Shear(semi-rigid,simple)connectionMoment(rigid)connectionTypeofstructuralelementsthatmadeuptheconnectionsSingleplateangleconnectionsDoublewebangleconnectionsTopandseatedangleconnectionsSeatedbeamconnectionsTypeofmemberstheconnectionsarejoiningBeam-to-beamconnectionsColumn-to-columnconnectionsBeam-to-columnconnectionsHangerconnectionsEffectofconnectionsonstructuresMechanicalpropertyofconnectionsStrengthStiffnessStabilityNumberandcomplexityofconnectionsTimeforstaticalanalysisProductionofdrawingsProductionofconnectionInthefabricationshop–consumemuchofworkcontentSiteproduction–easeforerectionComponentsofConnectionsWeldingIsaprocessofjoiningmetalpartsbyfusingthemandfillinginwithmoltenmetalfromtheelectrode.Usedextensivelytojoinpartsandmembers,attachcleats,stiffeners,endplates,etc.andtofabricatecompleteelements.Isoneoftheoldestandreliablemethodsofjoining.AdvantagesofWeldingConnectionEnablesdirecttransferofstressbetweenmemberseliminatinggussetandspliceplatesnecessaryforboltedstructures.Hence,jointweightisminimum.Absenceofholesimprovestheefficiencyofthesection.Lessfabricationcost.Offerairtightandwatertightjoining,andhenceisidealforoilstoragetanks,shipsetc.Neatappearanceandenablestheconnectionsofcomplicatedshapes.Rigidity.Weldedjointsareasstrongorstrongerthanbasemetal.Lessstressconcentration.DisadvantagesofWeldingConnectionRequiresskilledmanpowerforweldingaswellasinspection.Non-destructiveevaluationmayhavetobecarriedouttodetectdefects.Weldinginfieldmaybedifficultduetolocationorenviroment.Weldedjointsarehighlypronetocrackingunderfatigueloading.Largeresidualstressesanddistortiondeveloped.ElectricarcweldingManualarcwelding:Usingahand-heldelectrodecoatedwithafluxwhichmeltsandprotectsthemoltenmetalWeldqualitydependsverymuchontheskillofthewelderAutomaticarcwelding:Acontinuouswireelectrodeisfedtotheweldpool.Aninertgasisblownovertheweldtogiveprotection.WeldTypesButtwelds Namedaftertheedgepreparation,i.e.singleanddoubleUandV.Buttwelds Filletweldsizeisspecifiedbytheleg.PartialbuttandfilletweldsDeeppenetrationfilletweldsCrack&defectscausedbyweldingContractiononcoolingcausescrackingintheweld.Hydrogenabsorptionisthemaincauseofhydrogen-inducedcrackinginheat-affectedzone.Lamellartearingalongaslaginclusionisthemainprobleminplates.FollowingdefectscausedbyfaultyweldingprocedureOver-reinforcementandundercuttingIncompletepenetrationandlackofside-wallfusionSlaginclusionsandporosityWeldinginspectionVisualinspectionforuniformityofweld;Surfacetestsforcracksusingdyesormagneticparticles;X-rayandultrasonicteststocheckfordefectsinsidetheweld;Onlyvisualandsurfacetestscanbeusedonfilletwelds;Buttweldscanbecheckedinternally,andsuchtestsshouldbeappliedtoimportantbuttweldsintension.BoltsNon-preloadedboltsHexagonheadordinaryboltwithnutandwasheristhemostcommonlyusedstructuralfastenerintheindustry.Commonstrengthgrades:4.6,4.8.Preloadedorfriction-gripboltsMadefromhigh-strengthsteel.Betightenedtogiveahighshanktension.Shearintheconnectedplatesistransmittedbyfriction.Usedwherestrongjointsarerequired,andamajoruseisinthejointsofrigidcontinuousframes.Mustbeusedwithhardenedsteelwasherstopreventdamagetotheconnectedparts.Surfaceincontactmustbefreeofmillscale,rust,paint,grease,etc.Caremustbetakentoensurethatboltsaretighteneduptotherequiredtension.MethodstoachieveshanktensionPart-turningTorquecontrolLoad-indicatingwashersandboltsConnectionDesignWelddesignStrengthcalculationofafilletweldisusingthroatthickness,whichistakenas0.7timesthesizeofleglength.Designofbuttweldsdependsontheweldingquality.Designstrengthisgenerallytakenasequaltothatoftheparentmetalprovidedmatchingelectrodeareused.Fullpenetrationdepthisensurediftheweldismadefrombothsidesorifbackingsrunismadeonabuttweldmadefromoneside.BoltsdesignDependingontheconnectionshapeandtheboltslocation,boltsareloadedintension,shearorincombinedtensionandshear.Fornon-preloadedbolts,ashearjointcanfailinthefollowingfourwaysByshearontheboltshank;Bybearingonthememberorbolt;Byshearattheendofthemember;Bytensioninthemember

ShearFailurescanbepreventedfromfollowingmeasuresFormodes1and2,providesufficientboltsofsuitablediameter;Providesufficientenddistanceformode3;Formode4,designtensionmembersforeffectivearea;

Fordirecttensionjoints,twomethodscannowpermittedSimplemethod–useareducedboltstrengthconsideringthepryingaction;Moreexactmethod–consideringthepryingforce;SimpleConnectionsforBuildingsSimpleconnectionsaredefinedasjointsbetweenmemberstotransferonlydirectforces.e.g.verticalshearinabeamtocolumnorbeamtobeamconnection,axialtensionorcompressioninalatticegirderchordsplice,columnbaseorcolumnspliceconnection.Onlybeusedinsituationswheresufficientbracingispresentthat,whenthejointsareassumedtofunctionaspins,adequateoverallstructuralresistanceispresent.Simpleconnectionsleadtoeasierfabricationanderection,therefore,likelytoproducethemostcost-effectivesteelframes.Simpleconnectionsshouldfunctionas“nominallypinned”forbothmomentcapacityandrotationalstiffnessandtheonlyformofloadtransferrequiredwillbetheverticalshear.Simpleconnectionswillnormallybeeitherfullyboltedorwillinvolveacombinationofshopweldingandsitebolting.Exceptforconnectionssubjecttovibration,untorquedboltedinclearanceholesshouldbeused.MomentConnectionsforContinuousBuildingsMomentconnections(alsocalledrigidconnections),carryaportionorfullmomentcapacity.Unbracedframesarenecessarytobemoment-resisting.Momentconnectionsareusuallyrequiredtotransmitshearforce-andsometimesaxialforce–aswell,butinpracticemomenttendstobetheprimeconcern.Elasticallyanalyzedcontinuousframecouldincorporaterigidandpartialstrengthconnections.Plasticallyanalyzedcontinuousframecouldincorporatefullstrengthandsemi-rigidconnections.MeansofFormingConnectionsPopularboltedmomentconnectionsusedinpracticeare:Endplateconnections–BeamtoColumn,BeamtoBeam,ColumntoColumn(flush,extended,gusseted,haunched).T-sectionsattachedtobothflanges–BeamtoBeamCoverplatespliceconnections–BeamtoBeam,ColumntoColumnPopularweldedmomentconnectionsare:Allwelded;Weldedflanges,boltedweb(ahybrid,foreaseoferection)BaseconnectionsVariantofendplateconnectiongenerallyusedPocketedconnectionscanalsobechosenBriefreviewforsteelmaterials

ClassificationofConnectionsTypeofconnectingmediumused,…Typeofinternalforcestheconnectionstotransmit,…Typeofstructuralelementsmadeupconnections,…Typeofmemberstheconnectionsarejoining,…ComponentsofConnectionsWeldAdvantagesLightweightImproveefficiencyofsectionDirecttransferofstressLessfabricationAirtightandwatertightjoiningNeatappearanceRigidHighstrengthDisadvantagesRequireskilledmanpowerforweldingaswellasinspectionNon-destructiveevaluationhastobecarriedouttodetectwelddefects.HighlypronetocrackingunderfatigueloadingLargeresidualstressesanddistortionaredeveloped.ReviewWeldtypesButtweldsFilletweldWelddefectscracksSlagWeldinspectionVisualinspectionforuniformityofweldSurfacetestsforcracksusingdyesormagneticparticlesX-rayandultrasonicteststocheckfordefec