土木工程专业英语 教学课件 作者 陈瑛 1.2. Determinate and Indeterminate Structures.ppt

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1、1.2DeterminateandIndeterminateStructures静定和超静定结构StaticallyDeterminateStructuresStructuresaresaidtobestaticallydeterminatewhentheforcesandreactionsproducedbyagivenloadingcanbecalculatedusingonlytheequationsofequilibrium.StaticallydeterminatestructureSt

2、aticallyDeterminateStructuresThesimplysupportedbeamshowninFigure1.3isstaticallydeterminate.Wecansolveforthethreeunknownreactionsusingtheequationsofequilibriumandthencalculatetheinternalforcessuchasbendingmoment,shearforce,andaxialforceatanygivenlocati

3、onalongthelengthofthebeam.StaticallydeterminatestructureStaticallyIndeterminateStructuresFourunknownreactionsThreeindependentequilibriumequations,StaticallyIndeterminateStructuresStaticallyindeterminatebeamSaticallyindeterminateframeSaticallyindetermi

4、natecompositeStructuresForceMethod力法Theforcemethod(alsocalledtheflexibilitymethod)isusedtocalculateinternalforcesandreactionsinstaticallyindeterminatestructuresduetoloadsandimposeddeformations.ForceMethod力法Thestepsintheforcemethod1．Determinethedegreeo

5、fstaticalindeterminacyofthestructure.Parameternwillbeusedtodenotethedegreeofindeterminacy.确定超静定次数FPFPFAxFAyMAX1静定结构AABBCCThestepsintheforcemethod2Transformthestructureintoastaticallydeterminatesystembyreleasinganumberofstaticalconstraintsequaltothedeg

6、reeofstaticalindeterminacy,n.FPFPFAxFAyMAX1基本体系AABBCCprimarysystemThestepsintheforcemethodThisisaccomplishedbyreleasingexternalsupportconditionscreatinginternalhinges.Thesystemthusformediscalledtheprimarysystem.Numberthereleasedconstraintsfrom1ton.pri

7、marysystemqqqAABBCCllX1X1b)基本体系a)一次超静定结构3．Foragivenreleasedconstraintj,introduceanunknownredundant[ri5dQndEnt]forceXjcorrespondingtothetypeanddirectionofthereleasedconstraint.多余未知力redundantforce基本体系沿多余未知力方向的位移应与原结构位移相同FPFPFAxFAyMAX1基本体系AABBCCqqqAABBCC

8、llX1X1X14．Applythegivenloadingorimposeddeformationtotheprimarysystem.Calculatedisplacementsduetothegivenloadingateachofthereleasedconstraintsintheprimarysystem.ThesedisplacementsarecalledΔ1P,Δ2P,ΔnP..,.FPAABBCΔ1PX1ABX1=1d11Δ11=d11X1FPABCEIl/2l