惯性力和塑性铰_香港科技大学余同希讲座PPT

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1、CHAPTER4.INERTIAFORCEANDPLASTICHINGE惯性力和塑性铰41Relationbetweenwavepropagationand4.1Relationbetweenwavepropagationandglobalstructuralresponse4.2Inertiaforcesinslenderbars14.3Plastichingesinapulse-loadedrigid-plasticfree-freebeam4.1RELATIONBETWEENWAVEPROPAGA

2、TIONANDGLOBALSTRUCTURALRESPONSE波传播与结构总体响应间的关系2INTRODUCTIONResponseofastructureTiToquasi-sttilditaticloading:dfdeformatition,stitrainandtdstressTointensedynamicloading:wavepropagation;inertiaeffectForbeams,arches,plates,shells,onedimension(thickness)<

3、

4、akesWavepropagationoccursonlyinthesameorderoftimethatittakesastresswavetopropagatethroughthethicknessofthestructuretypicallyfewmicrosecondsAfterthrough-thikthicknesswavereflectsseveralltitimes,thestressalongthicknessdirectiondramaticallyreduces,whileea

5、chcross-sectionmovesasanentirety.Thislong-termdynamicbehavioriscalled(global)strctralresponsestructuralresponseseveralmillisecondsormuchlongerForstructuralresponseForstructuralresponseearlytimewavepropagationisdisregardedbuttheinertiaofthestructurest

6、illplaysessentialroletheexternalllloadidisassumedtidtoimpartmomentuminstantaneousltlytothemiddlesurfaceofthestructure44.2INERTIAFORCESINSLENDERBARS细长杆中的惯性力5INERTIAFORCORCSESAfterdynamicloading,aninitiallystationarystructuralmember(egaslenderbar)beginst

7、ostructuralmember(e.g.aslenderbar)beginstoaccelerateDDAlembert’Alembertprinciple:Theaccelerationfieldgivesprinciple:TheaccelerationfieldgivesrisetoadistributedinertiaforceaccelerationIngenerallttogetherwithFFexternalloads,theinertiaforcesproducebending

8、forcesproducebending,shearandaxialforcesininertiaforcethestructurethestructureRdynami‘ic‘equilibiilibrium’6NOTATIONSANDSIGNCONVENTIONSFORSLENDERBARSANDBEAMSQ(x)q(x)M+dMxdxM(x)yq(x)dxQ+dQForceequilibrium:QdQQqdx0dQ