土木工程专业英语 教学课件 作者 陈瑛 3.2.Limit State Design.ppt

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1、3.2LimitStateDesignLimitstatedesignrequiresthestructuretosatisfytwoprincipalcriteria:ultimatelimitstate承载能力极限状态serviceabilitylimit正常使用极限状态UltimateLimitStateAstructureisdeemedtosatisfytheultimatelimitstatecriteriaifalldesignvaluesofloadeffectcombination荷载效应组合arebelowthedesignvaluesofbearing

2、capacity承载能力calculatedforthesectionunderconsideration.UltimateLimitStatestructuralcollapseofallorpartofthestructure(verylowprobabilityofoccurrence)andlossoflifecanoccur.Lossofequilibriumofapartorallofastructureasarigidbody(tipping使倾斜,推倒,使倾覆,slidingofstructure).UltimateLimitStatesRuptureofc

3、riticalcomponentscausingpartialorcompletecollapse.(flexural,shearfailure).UltimateLimitStatesFormationofaplasticmechanism-yieldingofreinforcedformsplastichingesatenoughsectionstomakestructureunstable.Instabilitycasedbydeformationsofstructurecausingbucklingofmembers.Fatigue-memberscanfractu

4、reunderrepeatedstresscyclesofserviceloads(maycausecollapse).ServiceabilityLimitStateAstructureisdeemedtosatisfytheserviceabilitylimitstatewhentheconstituentelementsdonotdeflectbymorethancertainlimitslaiddowninthebuildingcodes,thefloorsfallwithinpredeterminedvibrationcriteria,andcrackwidths

5、inconcretearekeptbelowspecifieddimensions.SimplysupportedBeamCantileverbeamServiceabilityLimitStatesFunctionaluseofstructureisdisrupted,butcollapseisnotexpectedMoreoftentoleratedthanananultimatelimitstatesincelessdangeroflossoflife.Excessivecrackwidthleakagecorrosionofreinforcementgraduald

6、eteriorationofstructure.ServiceabilityLimitStatesMoreoftentoleratedthanananultimatelimitstatesincelessdangeroflossoflife.ExcessivedeflectionsfornormalservicecausedbypossibleeffectsmalfunctionofmachineryvisuallyunacceptableServiceabilityLimitStatesMoreoftentoleratedthanananultimatelimitstat

7、esincelessdangeroflossoflife.ExcessivedeflectionsfornormalservicecausedbypossibleeffectsdamageofnonstructuralelementschangesinforcedistributionspondingonroofscollapseofroofServiceabilityLimitStatesMoreoftentoleratedthananultimatelimitstatesincelessdangerofloss