土木工程专业英语 课件 6.4.Analysis of Rigid Reinforced Concrete Frame Structures

6.4AnalysisofRigidReinforcedConcreteFrameStructuresRigidFrameBehavior框架结构性能(a)Forcesanddeformationscausedbyexternalshear(b)Forcesanddeformationscausedbyexternalmoment框架总体剪切变形

框架总体弯曲变形

RigidFrameBehavior框架结构性能RigidFrameBehaviorTheshearcausesthestorey-heightcolumnstobendindoublecurvaturewithinflectionpoints反弯点

atapproximatelymid-storey-heightlevels.Themomentsappliedtoajointfromthecolumnsaboveandbelowareresistedbytheattachedgirders,whicharealsobentindoublecurvature,withinflectionpointsatapproximatelymid-span.RigidFrameBehavior

Thesedeformationsofthecolumnsandgirdersallowrackingoftheframeandhorizontaldeflectionineachstorey.Theoveralldeflectionshape总体变形

ofarigidframestructureduetorackinghasashearconfiguration剪切变形

withconcavity凹度upwind,amaximuminclinationnearthebase,andaminimuminclinationatthetop框架总体剪切变形

RigidFrameBehaviorTheoverallmomentoftheexternalhorizontalloadisresistedineachstoreylevelbythecouple

力偶

resultingfromtheaxialtensionandcompressiveforcesinthecolumnsonoppositesidesofthestructure.Theextensionandshorteningofthecolumnscauseoverallbending总体弯曲

andassociatedhorizontaldisplacementofthestructure.框架总体弯曲变形

RigidFrameBehaviorBecauseofthecumulativerotationuptheheight,thestoreydrift层间位移

duetooverallbendingincreaseswithheight,whilethatduetorackingtendstodecrease.Consequentlythecontributiontothestoreydriftfromoverallbendingmay,intheuppermostlevel,exceedthatfromracking.框架总体弯曲变形

Thecontributionofoverallbendingtothetotaldrift,however,willusuallynotexceed10%ofthatrackingexceptverytall,slender,rigidframes.Thereforetheoveralldeflectionshapeofahigh-riserigidframeusuallyhasashearconfigurationRigidFrameBehaviorTheresponseofarigidframetogravityloadingNegativemomentsareinducedadjacenttothecolumns,andpositivemomentsofusuallylessermagnitudeoccurinthemid-spanregions.RigidFrameBehaviorThecontinuityalsocausesthemaximumgirdermomentstobesensitivetothepatternofliveloading.Thismustbeconsideredwhenestimatingtheworstmomentconditions

ApproximateDeterminationofMemberForcesCausedbyGravityLoading:FloorFrameSubstructureMethod分层力矩分配法Forbuildingframeswitharegularoutline,notinvolvingunusualasymmetryofloadingorshape,theinfluenceofsidewaycausedbyverticalloadscanbeneglected.框架的侧移忽略不计MomentsduetoverticalloadsaredeterminedwithsufficientaccuracybydividingtheentireframeintosimplesubframesApproximateDeterminationofMemberForcesCausedbyGravityLoading:FloorFrameSubstructureMethod分层力矩分配法Eachofsubframesconsistsofonecontinuousbeam,plusthetopandbottomcolumnsframingintothatparticularbeam.Thefarendsofthecolumnsareconsideredfixed柱端设为固定端ApproximateDeterminationofMemberForcesCausedbyGravityLoading:FloorFrameSubstructureMethod分层力矩分配法Onlytwocyclesarecarriedoutintheanalysis.Momentstransferredfromonefloortoanotherflooraresmall.Hence,themomentsforeachfloorareseparatelycalculated.每层梁上的竖向荷载对本层梁及与本层梁相连的柱产生弯矩分层法计算步骤及要点1.选择某榀框架作为计算单元2.计算梁柱线刚度以及节点处分配系数

1）对于现浇框架，要考虑梁有效截面惯性矩的调整；

2）柱端设为固定端；

3）底层柱固定在基础顶面，可以视为固定端，其它层柱要考虑到实际有柱端转动，故上层各柱线刚度乘以0.9修正系数；

4）梁和底层柱的传递系数(carry-overfactor)按远端(farendsofmembers)固定，取1/2；上层各柱的传递系数取1/3。3.统计各层梁上竖向荷载(GravityLoading)设计值，并计算梁的固端弯矩(fixed-endmoment)。4.按前面规定的分配系数(distributionfactor)和传递系数(carry-overfactor)，采用力矩分配法(MomentDistributionMethod)对每一层框架分别进行计算。5.求得每层内力后，将同属于上下两层的柱弯矩值进行叠加，作为原框架该柱的最终弯矩，梁的弯矩仅属于本层，不需叠加。6.得到框架最终弯矩图后，根据节点静力平衡可求得梁跨中弯矩，支座剪力以及柱剪力和轴力。例题Thegravityloadaxialforceinacolumnisestimatedfromtheaccumulatedtributarydead

andlivefloorloadingabovethatlevel,withreductionsinliveloading

活荷载折减aspermittedbydesigncode.Theresistancetomomentsatanyfloororroofleveisestimatedbytakingthemaximumdifferenceoftheendmomentsintheconnectedgirdersanddistributingthemomentbetweencolumnsimmediatelyaboveandbelowthegivenfloorinproportiontotherelativecolumnstiffness.

6层5层2-4层1层ApproximateDeterminationofMemberForcesCausedbyHorizontalLoadingAllocationofLoadingBetweenColumnsAssumption：floorslabsarerigidinplaneForasymmetricstructuresubjectedtosymmetricloadingTotalexternalshearatalevelwillbedistributedbetweenthecolumnsinproportiontotheirshearrigidities抗侧刚度(D0)atthatlevel.Theshearrigidityofacolumnislinearrigidityofcolumn

heightofthestoreyApproximateDeterminationofMemberForcesCausedbyHorizontalLoadingInflectionPointMethod反弯点法Theinflectionpointsofallmembers,columnsandgirders,arelocatedmidwaybetweenjointsexceptthatofthegroundfloor.对上层柱，假定各柱上下转角相等，则柱上下端弯矩相等，反弯点在柱中央Theinflectionpointsofthegroundfloorcolumnsareassumedtobeatadistance2/3hfromthebottom.对于底层柱，柱脚转角为零，而上端转角不为零，故反弯点向上端移动铰接：无约束作用，弯矩为零，自由转动；固接：约束作用强，弯矩很大，转角为零。InflectionPointMethod反弯点法Thehorizontalshearatamid-storeylevelofstoreyiissharedbetweenthecolumnsinproportiontotheshearrig