外文翻译组合作用的基础及抗剪连接.docx
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外文翻译组合作用的基础及抗剪连接.docx
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外文翻译组合作用的基础及抗剪连接
外文翻译--组合作用的基础及抗剪连接
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FundamentalsofCompositeActionandShearConnection
Theevolutionofsatisfactorydesignmethodsforcompositebeamshasbeenaslowprocess,requiringmuchtheoreticalandexperimentalworkinorder'toprovideeconomicand,atthesametime,safedesigncriteria.ThepurposeofthisChapteristodescribeinsomedetailthemoreimportantfundamentalswhichhavetobetakenintoaccountinthedesignofcompositestructures.
Historicallythefirstanalysisofacompositesectionwasbasedontheconventionalassumptionsoftheelastictheorywhichlimitthestressesinthecomponent'materialstoacertainproportionoftheir'failurestresses(yieldinthecaseofsteel,crushinginthecaseofconcrete).Theassumptionsinherentintheelasticmethodaresimilartothoseforordinaryreinforcedconcrete.Inrecent'yearstheconceptsoftheultimateloaddesignphilosophyhavebeenappliedtocompositeactionandabodyofexperimentalevidencehasshownittobeasafe,economicalbasisonwhichtoproportioncompositesections.Althoughatthepresenttimeultimateloaddesignmethodsaredirectlyapplicableonlytobuildingsandnottobridgesthereseemsnoreasontodoubtthatintimetherestrictionwilldisappear.
Beforedealingindetailwiththetwodesignapproaches(elasticandultimateload)basicpointsrequireconsideration.
Aclearunderstandingofthewayinwhichthecomponentmaterials,steelconcreteandshearconnectionreacttoappliedloadisanessentialpreliminarytofullanalysisofthecompositesection.Ofprimaryimportancearethestressstrainsrelationships,whichmustofnecessitybetheproductofcarefullycontrolledexperiment.Theseexperimentalresultsarenotgenerallysuitedtodirectapplicationandsosimplificationsandidealisationsareadoptedinpractice.Theuseofcomputershasmadeitpossibletoreducetheamountofidealisationrequiredwiththeresultthatcomputer`experiments'cannowbeperformedusingmaterialstress-strainrelationshipsofconsiderablecomplexity.
Compositeactionbetweensteelandconcreteimpliessomeinterconnectionbetweenthetwomaterialswhichwilltransfershearbetweenthem.Inreinforcedconcretemembersthenaturalbondofconcretetosteelisoftensufficienttodothis,althoughcasesdoariseinwhichadditionalanchorageisrequired.Thefullyencasedfillerjoistalsohasalargeembeddedareawhichisadequateforfullsheartransfer.However,thesituationisquitedifferentwiththecommontypeofcompositebeaminwhichtheconcreteslabrestson,oratbestencloses,thetopflangeofthesteelbeam.Itistruethattherewillinitiallybesheartransferbybondandfrictionatthebeam-slabcontactsurface.Thereis,however,atendencyfortheslabtoseparateverticallyfromthebeamand,shouldthisoccur,horizontalsheartransferwillcease.mAsingleoverloadorthefatigueeffectofpulsatingloadingmaydestroythenaturalbond,whichoncedestroyedcannotbereconstituted.Theimponderablenatureofsuchshearconnectionisclearlyundesirable;someformofdeliberateconnectionbetweenbeamandslabisrequiredwiththetwoobjectsoftransferringhorizontalshearandpreventingverticalseparation.A,naturalbondwillexistinthepresenceofshearconnectionbutitisneitherdesirabletocountonitsexistencenorpossibleinallcasestocalculateitsvalue.Thusshearconnectionmustbeprovidedtotransferallthehorizontalshearforce.
Ithas.beenpointedoutthattheparadoxicalsituationexiststhatifshearconnectionisprovideditmayinfactnotcomeintooperationbecausethenaturalbondtakesalltheisprovideditmayinfactnotcomeintooperationbecausethenaturalbondtakesalltheshearforce,andso`ifsufficientshearconnectorsareprovidedthentheyareunnecessary'.
Theevolutionofshearconnectiondeviceshasbeenslowandhasnecessitatedalargevolumeofexperimentalworkonthestaticandfatiguepropertiesofawiderangeofmainlymechanicalconnectors.
Itsoonappearedcleartoearlyresearchworkersthatsomeformofconnectorfixedtothetopflangeofthebeamandanchoredintotheslabwasnecessary.CaugheyandScottin1929proposedusing,amongstotherthings,projectingboltends.Sincethenawidevarietyoftypesofmechanicalconnectorhasbeenusedinexperimentandpractice.Tosomeextenttheproliferationoftypeshasbeen.theresultofsteelfabricatorsusingsectionswhichcameeasilytohand,sinceinitiallyapurpose-madeshearconnectorwasnotavailable.
Inanymechanicalconnectionsystemitispossibletoidentifypartswhichtransferhorizontalshearandpartswhichtietheslabdowntothebeam.Generally,horizontalshearresistanceistherulingcriterionofshearconnectoractionandwiththisinmindmechanicalconnectorsmaybeclassifiedintothreemaingroups-rigid,flexibleandbond.
LimitStateDesignofBrickwork
Thebasicaimofstructuraldesignistoensurethatastructureshouldfulfillitsintendedfunctionthroughoutitslifetimewithoutexcessivedeflection,crackingorcollapse,andthisaimmustofcoursebemetwithdueregardtoeconomy.Thedesignerisassistedinhistaskbytheavailabilityofacodeofpracticewhichisbasedonaccumulatedexperienceandresearch.Uptothepresenttime,suchcodeshavesoughttoensurethesafetyandserviceabilityofmasonrystructuresbyspecifyingpermissiblestressesforvarioustypesandcombinationsofmaterials.Thuscodesgenerallygivebasiccompressivestressesforarangeofbrick-mortarcombinations;thebasicstressinaparticularcasehasthentobeadjustedfortheslendernessratiooftheelementandtheeccentricityoftheloading.Thebasicstressesarederivedfromtestsonwallsorpiers,theultimatestresseshavingbeendividedbyanarbitraryfactorofsafetysufficientlylargetoavoidcrackingatworkingloads.Thus,tothisextent,brickworkdesignhasalwaysbeenrelatedtoultimatestrengthandtoaserviceabilitylimitstate.
Inrecentyearsamorerationalprocedurehasbeenevolvedfordealingwithstructuralsafetyandserviceabilitythroughconsiderationoftherelevant"limitstates“.Astructure,orpartofastructure,reachesalimitstatewhenitbecomesincapableoffulfillingitsfunctionorwhenitnolongersatisfiestheconditionsforwhichitwasdesigned.Twocategoriesoflimitstatenormallyhavetobeconsidered,namely,ultimatelimitstatescorrespondingtofailureorcollapseandserviceabilitylimitstatesatwhichdeflectionsorcrackingbecomeexcessive.
ThegeneralmethodofapplyingthelimitstatesapproachtothedesignofstructuresisoutlinedinapublicationoftheInternationalOrganizationforStandardizationinwhichthecriterionforasatisfactorydesignisexpressedintermsofdesignloadingeffects(S*)anddesignstrengths(R*)asfollows
(1)
Designloadingeffectsaredeterminedfromthecharacteristicactionsfromtherelationship
S*=effectsof(
)
(2)
whereγfisamultiplier(orpartialsafetyfactor)and
isacharacteristicloadwhich,ifdefinedinstatisticalterms,isgivenby
where
isthevalueofthemostunfavourableloadwitha50percentprobabilityofitsbeingexceededonceintheexpectedlifeofthestructureδisthestandarddeviationofthedistributionofthe.maximumloadingkisacoefficientdepefldin8onaselectedprobabilityofmaximumloadingsbeinggreaterthan
Itisusualtotakethecharacteristicloadasthatwhichwillhavea5percentprobabilityofbeingexceededduringthelifetimeofthestructure.④Inmanysituations,however,statisticaldataarenotavailableandthecharacteristicloadshavetobebasedonnominalvaluesgivenincodesofpracticeorotherregulations.Thefactorγfisafunctionofseveral
partialcoefficients.
whichtakesaccountofthepossibilityofunfavourabledeviationoftheloadsfromthecharacteristicexternalloads,thusallowingforabnormalorunforeseenactions
whichtakesaccountofthereducedprobabilitythatvariousloadsactingtogetherwilla11besimultaneouslyattheircharacteristicvalues.
whichisintendedtoallowforpossiblemodificationoftheloadeffectsduetoincorrectdesignassumptions(forexample,introductionofsimplifiedsupportconditions,hinges,neglectofthermalandothereffectswhicharedifficulttoassess)andconstructionaldiscrepanciessuchasdimensionsofcross-section,deviationofcolumnsfromtheverticalandaccidentaleccentricities.
Similarly,designstrengthsofmaterials,R*,aredefinedby
R*﹦
where
--Rm-ksisthecharacteristicstrengthofthematerial
Rmisthearithmeticmeanoftestresults
sisthestandarddeviation
kisacoefficientdependingontheprobabilityofobtainingresultslessthan
Thecharacteristicstrengthofamaterialisusuallytakenasthe95percentconfidencelimitofthematerialstrengthinarelevanttestseries.Thereductioncoefficientγmis
afunctionoftwocoefficients
whichisintendedtocoverpossiblereductionsinthestrengthofthematerialsinthestructureaswholeascomparedtothecharacteristicvaluededucedfromthecontroltestspecimen
whichisintendedtocoverpossibleweaknessofthestructurearisingfromanycauseotherthanthereductioninthestrengthofthematerialsallowedforbycoefficientγm1,includingmanufacturingtolerances.
Additionally,ISO2394allowsfortheintroductionofafurthercoefficient
whichmaybeappliedeithertothedesignvaluesofloadingsormaterialstrengths.Thiscoefficientisinturnafunctionoftwopartialcoefficients
whic
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