Lecture 06.docx
- 文档编号:3565238
- 上传时间:2022-11-23
- 格式:DOCX
- 页数:54
- 大小:212.26KB
Lecture 06.docx
《Lecture 06.docx》由会员分享,可在线阅读,更多相关《Lecture 06.docx(54页珍藏版)》请在冰豆网上搜索。
Lecture06
StructuralSteelworkEurocodesDevelopmentof
ATrans-nationalApproach
Course:
Eurocode3
Module3:
Framedesignapproaches
Lecture6:
Choiceofanalysisandimplicationsfordesign
Summary:
∙Thelectureintroducestheideathatthechoiceoftheanalyticaltoolisguidedpartlybythemethodofdesigntobeused(includingEurocode3Part1-1restrictions)andpartlybytheuserasafunctionofsoftwareavailability.Themoresophisticatedtheanalysistoolis,thelessaretheresultingdesigntasksaftertheanalysis.
∙Thedifferentmethods,“ direct ”and“ indirect ”,forsecond-orderanalysisareoutlinedandtheconsequencethateachhasforthedesignoftheframeanditscomponentsisexplained.
∙Useofelastic(linearandnon-linear),first-orderrigid-plasticandelastic-plasticmethodsofanalysisanddesignarediscussed.
∙FlowchartsandguidelinesintabularformareprovidedtohelpthedesigneridentifytherelevantparagraphsofEurocode3Part1-1tobeappliedateachstepoftheanalysisanddesignprocedure.
Pre-requisites:
∙Aknowledgeofthefundamentalsofthetheoryofresistanceofmaterials(forbeamsandtensionmembers)andofstructuralanalysis.
∙Aknowledgethebasictheoryofcolumnbucklingandotherformsofinstability.
∙Aknowledgeoftheelasticandplasticdesignofsimplemembers.
∙Module1forLoadinganddefinitionsofLimitStates.
∙Lecture4“Frameidealisationandanalysis”.
∙Lecture5“Frameclassificationandjointrepresentation”.
NotesforTutors:
∙Thismaterialcomprisesone75minutelecture,althoughsomeselectionofthematerialwillhavetobemadetomaintainthattimelimit.
Objectives:
Thestudentshould:
∙Understandthedifferencestherearebetweenchoosingamoreorlesssophisticatedanalyticaltool.
∙Recognisetherearecaseswhereagiventypeortypesofanalysesareexcluded,butthatoftenthereareanumberofvariousmethodswhichmaybeemployedtopredictthestructuralresponse.
∙Appreciatethelinksbetweenvariousanalyticalanddesignapproaches.
References:
[1]King,C.M.,Plasticdesignofsingle-storeypitched-roofportalframestoEurocode3,SteelConstructionInstitute,TechnicalReport,SCIPublication147,1995.
[2]Merchant,W.,Framestabilityintheplasticrange.,Brit.Weld.Jour.;N°3,(366),1956.
[3]Wood,R.H.,Effectivelengthofcolumnsinmulti-storeybuildings,TheStructuralEngineer,N°7,8and9,Vol.52,1974.
[4]KirbyP.A.,NethercotD.A.,Designforstructuralstability,Collins,London,1988.
[5]JaspartJ-.P.,Ultimateloadofframeswithsemi-rigidjoints,J.Const.SteelRes.,Vol.11,No.4,1988.
[6]ENV1993-1-1:
Eurocode3:
Designofsteelstructures:
Part1-1:
Generalrulesandrulesforbuildings.
1Generalconsiderationsaboutthechoiceofanalysis
1.1Choicebetweenafirst-orderorasecond-orderanalysis
Atthepreliminarydesignstageadecisionusuallyhastomadeastowhetherthestructureistohaveabracedorunbracedclassification.Thisdetermineshowtheverticalandhorizontalloadeffects(includingthoseduetoframeimperfections)aretobeconsideredintheanalysis.
5.2.5.3
Oncetheframeconfigurationhasbeenestablished,preliminarydesignforthemembersandjointpropertiesisundertaken.Apreliminaryanalysiscanbeusedtodeterminetheframeclassificationasswayornon-sway.Alternatively,onemayassumeaframeclassificationtobeverifiedlater.Basedonthisinformation,onemustchooseanappropriatemethodofglobalanalysisfordeterminingthedesigninternalforcesandmoments.Formosttypicalframesafirst-orderanalysiswillbeadequate.
Whereasasecond-order,elasticorplastic(butundercertainmemberandjointclassificationconditions),analysiscanalwaysbeused,therearecaseswhere:
5.2.1.2(3)
∙afirst-orderanalysissuffices,withouttherebeinganyneedtoaccountforsecond-ordereffects,
5.2.1.2(2c)
∙whenVSd/Vcr0,25,afirst-orderelasticanalysiscanbeusedfortheanalysisofswayframes,withcorrectionstoaccountforsecond-ordereffectswhentheyaresignificant.
5.2.6.2(4)
∙arigid-plasticfirst-orderanalysiscanbeusedwhenVSd/Vcr0,20andonconditionthatalltheinternalforcesandmomentsareamplifiedby1/(1-VSd/Vcr.).ThiscaseisinfactanapplicationoftheMerchant-RankineApproach[1].
5.2.6.3(3)
Inordertomakethischoice,itisnecessarytoevaluatethedegreetowhichthesecond-ordereffectsmaymodifythedistributionofinternalforces(i.e.,evaluatewhetherswaydisplacements(P-)andmemberimperfections/memberdeformations(P-)aresignificantornot).Itisrecalledthattheswaydisplacementshavethemostdominanteffectinaswayframe.Whilethememberimperfectionandmemberdeformationeffectsmaybesignificantforcertaintypesofrelativelyslendermembersinaswayframe,theyareunlikelytobesoformembersinanon-swayframe.
5.2.5.2
5.2.4.2(4)
Forthepurposeofexaminingtheeffectofsway,onemustevaluatethecriticalloadparametercr,i.e.theratiobetweenthetotalverticalloadwhichwouldproducein-planeswayinstabilityoftheframeandtheactualdesignverticalloads.(Eurocode3Part1-1usestheinverseofthisparameter,thatis1/cr=VSd/Vcr,forthisevaluation).Oncecolumnsaregivenpreliminarysizes,anestimatecanbemadebasedonthevalueofVSd/Vcrforthemostlikelycriticallyloadedcolumnsoftheframe.Thispreliminaryevaluationneedstobeverifiedonceananalysishasbeencarriedout.
Anapproximateapproachforthecalculationofthisparameterformulti-storeybuildingscanbeused(seelecture5).Howeverthisapproachisnotsuitedforusefortypicalone-storeypitched-portalindustrialframebuildings.ForthiscasereferenceshouldbemadetothedesignexampleonsuchatypeofstructureandtoKing[1].
5.2.6.2(6)
Whenthevalueofcrissufficientlylarge,i.e.,cr10(oralternativelystatedVSd/Vcrissufficientlysmall0,1)theframeisclassifiedasnon-swayandafirst-orderanalysisisadequate.
5.2.5.2(3)
Whentheframeisclassifiedasaswayframe,asecond-orderanalysisisrequired.However,formanystructures,itisstillpossibletoconductafirst-orderanalysis,onconditionthattheinternalforcesandmomentssoobtainedareamplifiedappropriatelytoaccountforsecond-ordereffects(i.e.byanindirectmethod).
Thememberdeformationeffectmaybeofconcernforrelativelyslenderbeam-columnmembersofbothswayandnon-swayframes.Whiletheuseofslendermembersinframesisnotcommon,itisprudenttocheckwhetheronemusttakeaccountofthememberdeformationeffectinthemornot.EC3mentionstheneedtoexaminetheimportanceoflocalmemberimperfectionsforcertaintypesofbeam-columninswayframesonly.Intheabsenceofaspecificrequirementabouttheeffectofmemberdeformationsduetoload,thecheckformemberimperfectionsignificancemayalsobeconsideredasanevaluationofthesignificanceofthelocalsecond-ordereffects(P-)onagivenmember,whateverthesource.Theprocedureusedtoidentifytheslendermembersconcernedisquitesimilartothatfortheframeswayclassification.Thedifferenceisthattheparameterusedisnowthevalueof1/cr=NSd/Ncrforthebeam-columnmemberalone.WhenNSd/Ncr0,25foranysuchmember,thenitisnecessarytointroducememberimperfections(atleastforthemembersconcerned)intheglobalanalysisandtouseageneralsecond-orderanalysis.InthecalculationofNcr(theEulerload)oneusesabucklinglengthforthememberequaltothesystemlength.Theimperfectiontobeusedisspecifictothetypeofmemberusedandtherelevantbucklingcurve.
5.2.4.2(4)
5.5.1.3
1.2Choiceofjointrepresentationintheframeidealisation
Thisquestionisdiscussedinlecture7“ Traditionalandmoderndesignapproaches ”.
1.3Choicebetweenelasticandplasticmethodsofanalysis
Thedesignermustalsodecidebetweenusinganelasticmethodofanalysis,andaplasticmethodofanalysisAplasticmethodofanalysisisonlyappropriateundercertainconditionssuchassteelproperties,membercross-sectionclassificationandjointductility.
Thedesigncheckstobecarriedoutafteranalysisdependonthesophisticationoftheanalysistoolused.Forinstancewhensecond-orderanalysisisusedthereisusuallynoneedtocheckin-planestabilityoftheframeorofitsmembers.ThechoiceofglobalanalysiswillthusdependnotonlyonwhatisrequiredbyEC3,butalsoonpersonalchoices,dependingonspecificsituations,availablesoftware,etc.Onemuststrikeabalancebetweentheamountofeffortdevotedtoglobalanalysis,andtheamountofeffortrequiredforremainingULSchecks(seeFigure1).
Thecriteriawhichmustbemetfortheapplicationofagivenmethodofanalysisandtheimplicationsfordesignareidentifiedinthefollowingparagraphs.Withthisknowledgeadesignershouldbeinapositiontomakethebestchoiceamongstthetoolsathisorherdisposition.Itisclearthatthechoiceofthemethodofanalysisdependstoaconsiderableextentuponthedesignmethodonewishestouse.Forinstance,theapplicationofplasticdesignissubjecttorestrictionsandrequiresparticularmethodsofanalysis.Whateverthedesignmethodchosen,itisofparticularlyimportancetoidentifywhensecond-ordereffectsneedtobeaccountedfor.Forthemanytypicalplaneframesanyofthemethodsofanalysismaybeused.
Figure1BalanceofeffortbetweenglobalanalysisandULSchecks
GuidelinesinatabularformaregiveninAnnex1fortheapplicationofthevariousmethodsofanalysis.Thetablesprovideastep-by-steppro
- 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 06