Lecture 16.docx
- 文档编号:15958442
- 上传时间:2023-07-09
- 格式:DOCX
- 页数:18
- 大小:160.98KB
Lecture 16.docx
《Lecture 16.docx》由会员分享,可在线阅读,更多相关《Lecture 16.docx(18页珍藏版)》请在冰点文库上搜索。
Lecture16
StructuralSteelworkEurocodesDevelopmentof
ATrans-nationalApproach
Course:
Eurocode3
Module5:
StructuralJoints
Lecture16:
SimpleJoints
Summary:
Thislectureisintendedtointroducetheconceptofsimplejointsasalimitingconditionofalljoints.
Therequirementsrelatingtostiffness,strengthandrotationcapacityarelisted.
Jointsaredescribedasanassemblageofcomponentseachofwhichmayberegardedasalinkinachain.Thestrengthoftheweakestlinkcontrolstheoverallloadcarryingcapacityofthesystem.
∙Examplesofsimplebeamtocolumnandbeamtobeamjointsaregiven.
Pre-requisites:
(whatpriorknowledgeisrequiredofthestudent?
)
∙Aknowledgeofstructuralanalysis
Helpful(butnotessential)tounderstandplasticresponseofframes
LectureonGeneralitiesaboutStructuralJoints
NotesforTutors:
Thismaterialcomprisesone30minutelecture.
Objectives:
Thestudentshould:
∙Understandtheconceptualassumptionofsimplejoints.
∙Appreciatethebasicreasoningfortheapproximation
∙Beabletoexamineajointandidentifytheindividualcomponentsandforcetransferswhichoccurinthejoint.
∙Knowwheretolookforclausesgoverningtheseforcetransfers.
∙Beabletoassessthecapacityofajointwhenworkedexampleshavebeenstudied.
References:
(essential&backgroundreading)
·Owens,G.W.andCheale,B.D.,”StructuralSteelworkConnections”,Butterworth&Co.,Salisbury,1989.
Kirby,P.A.,Bitar,SandGibbons,C.,”TheDesignofColumnsinNon-SwaySemi-RigidlyConnectedFrames”,FirstWorldConferenceonConstructionalSteelDesign,Acapulco,Mexico,December1992.
Contents
1.Introduction
1.1Condition1:
Strength
1.2Condition2:
Stiffness
1.3Condition3:
RotationCapacity
2.TypesofJoint
2.1BeamtoColumnJoints
2.2BeamtoBeamJoints
2.2.1PrimarytoSecondaryBeams
2.2.2BeamSplices
3.ConcludingSummary
1.Introduction
Beam-to-columnandbeam-to-beamjointsaretraditionallydesignedaspinnedorrigideventhoughthemostflexibleofthesewillprovidesomeresistancetomomentwhilstthestiffestwillhavesomesmalldegreeofflexibility.Aswasarguedinthelectureon“GeneralitiesofStructuralJoints”,simplejointsarepresumedtopossessnoresistancetomomentwhatevertherotationatthejoint.Inaframewhichispreventedfromswaying,thisassumptionmakesthestructurebehaveasacollectionofstaticallydeterminatecomponentswhichmaythenbereadilyanalysedbyhandand,equallyimportantly,eachmembermaybeproportionedwithoutreferencetotherestofthestructure.Ifthejointsareassumedtoberigid,theframemaybeanalysedusingarelativelystraightforwardanalysisthoughtheresultingcomputationsareconsiderablymorecomplexthanforapin-jointedframe.Itcanbeappreciatedthattheassumptionsregardingthepinnedandrigidapproximationshavearisenbecauseoftheresultingsimplificationsinframeanalysisandhenceinthedesignprocess.Althoughcomputationalcapabilitieshaveimproveddramaticallyduringthepastcoupleofdecades,mostframesarestilldesignedusingtheseassumptionswhichrepresentthelimitingmoment-rotationstiffnesseswhichcanexistinjoints.Thisimpliesthatframesdesignedusingtheassumptionofpinnedjointswillnotbecapitalisingontheinherentstiffnesspossessedbyeventhesimplestconnectionswhilstfamesdesignedusingcontinuousconstruction(rigidjoints)willprobablyinvolvetheexpenseofcomplexjointsoftenincorporatingtheuseofstiffenersinordertoachievetherequisitestiffnessinthejoint.Inreality,allpracticaljointshavemoment-rotationcharacteristicswhichcorrespondtostiffnessesintermediatebetweenthesetwoextremecases.
Inadditiontotheconsiderationofjointstiffnessreferredtoabove,thereisasecondfactorwhichmustbeaccountedforinjointdesign,namelystrength.Bydefinition,ajointwhichistrulypinnedpossesseszeroresistancetomoment.However,otherjointsmaybeeitherfullstrength-ifthemomentresistanceofthejointexceedsthatoftheconnectedmembers-orpartialstrengthifitsresistanceislessthanthatoftheconnectedmembers.Thissituationisalsodescribedinlecture4:
“FrameAnalysisandDesign”.
Tofullysatisfythedefinitionofatruepinnedjointwouldrequiretheproductionofanexpensivedetail.Thisisnotjustifiableas,formanyyears,designershavebeenproducinghighlysuccessfulframesusingtheassumption,andwithoutsuchexpense.Thereisarangeofsituationsforwhichsmallstiffnessandstrengthmaybeneglected.EC3statesthat“anominallypinnedconnectionshallbesodesignedthatitcannotdevelopsignificantmomentswhichmightadverselyaffectmembersofthestructure”.Clearlytheconnectionmustneverthelessbecapableofsuccessfullytransferringtheforcesarisingatthelocationandmustbecapableofundergoinganyrequireddeformationswithoutdistress.Thisimpliesthat,iftheframeisdesignedplastically,theconnectionmustbeabletorotatesufficientlytopermitallofthehingesofthemechanismtodevelop.Thisgivesrisetotherequirementofadequaterotationcapacity.Considerationofajointassumedtoresistzeromomentshowsthatsuchjointsmustalsobecapableofacceptingrotationwithoutlosingtheabilitytoresistactionssuchasshear.
Thusitcanbeseenthat,ingeneral,aconnectionhasthreedistinctproperties
(i)Strength-itsmomentresistance.
(ii)Stiffness-relatedtotheslopeofitsmoment-rotationrelationship.
(iii)Deformability-itsrotationcapacity.
Inordertodeterminewhetherornotaconnectionwillsatisfytheconditionthatmomentswillnotadverselyaffecttheperformanceoftheframe,considerableresearchhasshownthatabeamtocolumnconnectionmaybeclassifiedasnominallypinnedifthetwoconditionslistedbelow,aresatisfied.
1.1Condition1:
STIFFNESS
ThisrotationalstiffnessSjmustsatisfythecondition
Sj,ini0,5EIb/Lb
(1)
whereSj,iniistheinitialrotationalstiffnessoftheconnection.
Ibisthesecondmomentofareaoftheconnectedbeam.
Lbisthelengthoftheconnectedbeam.
IntheENVversionoftheEurocode,inChapter6,therelevantstiffnesswasspecifiedasSj,,whichwasmeasuredwithreferencetothepointonthemoment-rotationcharacteristicatthedesignmomentresistance,MRd.HoweverintherevisedAnnexJthishasbeenreplacedbytheinitialstiffness,Sj,ini.
Revised
AnnexJ
1.2Condition2:
STRENGTH
Thedesignmomentresistanceofthejoint,MRd,mustnotexceed0,25timesthedesignplasticmomentresistance,Mpl.Rd,oftheweakerconnectedmemberormembersasshowninFigure1.
Inadditiontosatisfyingtheaboverequirementsforajointdetailtobeconsideredtobeapinnedconnection,thedesignermustensurethattheshear(theendreactionofthebeam)andanyaxialforcecanbesafelytransferredbetweentheconnectedmembers.Theprincipalactiontobeconsideredisthetransferrenceofthereactionfromtheendofthebeamthroughtothesupportingmember.Thisreactionmayalsobeaccompaniedbyatyingforceanditmaybenecessarytocombinethesetwoactionstodeterminetheirresultant.
1.3Condition3:
ROTATIONCAPACITY
Afurtherconsiderationwhichisincludedrelatestotheabilityofthejointtoremaincoherentandacceptimposedrotationswithoutrupture(forexampleweldsmustnotfracture)beforesufficientrotationshaveoccurredwhichallowthefullloadingtobecarried,norshouldthejointacquireanundesirablestiffnessduringthedevelopmentoftherequiredrotations.
Consideringfirsttheproblemofthedevelopmentofanundesirablestiffness.Themostobvioussituationwhichmightgiverisetosuchaneffectistheclosureofagapwhichcausestwosurfacestocomeintobearing.Thismightleadtoanincreasedstiffnesswhichisinappropriateforsimpledesign,asindicatedinFigure2.Calculationsonamediumsizedbeam(about450mmdeep)andspanning6.0mshowsthattherotationsresultingfromtheapplicationofamaximumfactoredloadingcausesagapofsome10mmtobeproducedatoneextremityofthebeamend,iftherotationalendrestraintistrulyzero.Ofcoursethesizeofthisgapwillincreasewithbeamdepth.Inpracticetherewillalwaysbesomeresistancetorotationandthiswillreducethesizeofthegaprequiredandtheactualspanmomentwhichwillariseatthemidspanofthebeam.Thustheassumptionofzerorestraintissafeforbeams.Theeffectoncolumnsis,atfirstsight,somewhatdifferentasanymomentattractedtothejointwillbetransferredtothecolumn.Howeverextensivestudies,boththeoreticalandexperimental,havedemonstratedthattheeffectofanyadversemomenttransferredfromthebeamtothecolumnbecauseofthestiffnessofthejointisoffsetbytherestraintprovidedtothecolumnbythebeamduetothestiffnessofthejoint.Furtherinformationonthisphenomenonmaybefoundinthesecondofthereferences.
Theotherphenomenonwhichmustbeconsideredisthemodeoffailurewithinajoint.Forcleatedconnections,theproblemsassociatedwithoverstrengthmaterialiscoveredinrevisedAnnexJwherehiddenfactorshavebeenincludedintheformulationswhichcaterforthepossibilityofthiseffect.Theyensurethatfailureisintheanglesectionsanddoesnotoccurintheboltsthusensuringthataductile(ratherthanabrittle)failureoccurswhich,ingeneral,leadstoanadequaterotationcapacity.
2.TypesofJoint.
Themostcommonjointswhichareusedforsimpleconnectionsbetweenbeamsandcolumnsareseatandwebcleats,topandseatcleats,webcleats,flexibleendplateconnections
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- Lecture 16