土木工程專業(yè)英語 課件 6.4.Analysis of Rigid Reinforced Concrete Frame Structures

6.4AnalysisofRigidReinforcedConcreteFrameStructuresRigidFrameBehavior框架結(jié)構(gòu)性能(a)Forcesanddeformationscausedbyexternalshear(b)Forcesanddeformationscausedbyexternalmoment框架總體剪切變形

框架總體彎曲變形

RigidFrameBehavior框架結(jié)構(gòu)性能RigidFrameBehaviorTheshearcausesthestorey-heightcolumnstobendindoublecurvaturewithinflectionpoints反彎點

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

Thesedeformationsofthecolumnsandgirdersallowrackingoftheframeandhorizontaldeflectionineachstorey.Theoveralldeflectionshape總體變形

ofarigidframestructureduetorackinghasashearconfiguration剪切變形

withconcavity凹度upwind,amaximuminclinationnearthebase,andaminimuminclinationatthetop框架總體剪切變形

RigidFrameBehaviorTheoverallmomentoftheexternalhorizontalloadisresistedineachstoreylevelbythecouple

力偶

resultingfromtheaxialtensionandcompressiveforcesinthecolumnsonoppositesidesofthestructure.Theextensionandshorteningofthecolumnscauseoverallbending總體彎曲

andassociatedhorizontaldisplacementofthestructure.框架總體彎曲變形

RigidFrameBehaviorBecauseofthecumulativerotationuptheheight,thestoreydrift層間位移

duetooverallbendingincreaseswithheight,whilethatduetorackingtendstodecrease.Consequentlythecontributiontothestoreydriftfromoverallbendingmay,intheuppermostlevel,exceedthatfromracking.框架總體彎曲變形

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

ApproximateDeterminationofMemberForcesCausedbyGravityLoading:FloorFrameSubstructureMethod分層力矩分配法Forbuildingframeswitharegularoutline,notinvolvingunusualasymmetryofloadingorshape,theinfluenceofsidewaycausedbyverticalloadscanbeneglected.框架的側(cè)移忽略不計MomentsduetoverticalloadsaredeterminedwithsufficientaccuracybydividingtheentireframeintosimplesubframesApproximateDeterminationofMemberForcesCausedbyGravityLoading:FloorFrameSubstructureMethod分層力矩分配法Eachofsubframesconsistsofonecontinuousbeam,plusthetopandbottomcolumnsframingintothatparticularbeam.Thefarendsofthecolumnsareconsideredfixed柱端設(shè)為固定端ApproximateDeterminationofMemberForcesCausedbyGravityLoading:FloorFrameSubstructureMethod分層力矩分配法Onlytwocyclesarecarriedoutintheanalysis.Momentstransferredfromonefloortoanotherflooraresmall.Hence,themomentsforeachfloorareseparatelycalculated.每層梁上的豎向荷載對本層梁及與本層梁相連的柱產(chǎn)生彎矩分層法計算步驟及要點1.選擇某榀框架作為計算單元2.計算梁柱線剛度以及節(jié)點處分配系數(shù)

1）對于現(xiàn)澆框架，要考慮梁有效截面慣性矩的調(diào)整；

2）柱端設(shè)為固定端；

3）底層柱固定在基礎(chǔ)頂面，可以視為固定端，其它層柱要考慮到實際有柱端轉(zhuǎn)動，故上層各柱線剛度乘以0.9修正系數(shù)；

4）梁和底層柱的傳遞系數(shù)(carry-overfactor)按遠端(farendsofmembers)固定，取1/2；上層各柱的傳遞系數(shù)取1/3。3.統(tǒng)計各層梁上豎向荷載(GravityLoading)設(shè)計值，并計算梁的固端彎矩(fixed-endmoment)。4.按前面規(guī)定的分配系數(shù)(distributionfactor)和傳遞系數(shù)(carry-overfactor)，采用力矩分配法(MomentDistributionMethod)對每一層框架分別進行計算。5.求得每層內(nèi)力后，將同屬于上下兩層的柱彎矩值進行疊加，作為原框架該柱的最終彎矩，梁的彎矩僅屬于本層，不需疊加。6.得到框架最終彎矩圖后，根據(jù)節(jié)點靜力平衡可求得梁跨中彎矩，支座剪力以及柱剪力和軸力。例題Thegravityloadaxialforceinacolumnisestimatedfromtheaccumulatedtributarydead

andlivefloorloadingabovethatlevel,withreductionsinliveloading

活荷載折減aspermittedbydesigncode.Theresistancetomomentsatanyfloororroofleveisestimatedbytakingthemaximumdifferenceoftheendmomentsintheconnectedgirdersanddistributingthemomentbetweencolumnsimmediatelyaboveandbelowthegivenfloorinproportiontotherelativecolumnstiffness.

6層5層2-4層1層ApproximateDeterminationofMemberForcesCausedbyHorizontalLoadingAllocationofLoadingBetweenColumnsAssumption：floorslabsarerigidinplaneForasymmetricstructuresubjectedtosymmetricloadingTotalexternalshearatalevelwillbedistributedbetweenthecolumnsinproportiontotheirshearrigidities抗側(cè)剛度(D0)atthatlevel.Theshearrigidityofacolumnislinearrigidityofcolumn

heightofthestoreyApproximateDeterminationofMemberForcesCausedbyHorizontalLoadingInflectionPointMethod反彎點法Theinflectionpointsofallmembers,columnsandgirders,arelocatedmidwaybetweenjointsexceptthatofthegroundfloor.對上層柱，假定各柱上下轉(zhuǎn)角相等，則柱上下端彎矩相等，反彎點在柱中央Theinflectionpointsofthegroundfloorcolumnsareassumedtobeatadistance2/3hfromthebottom.對于底層柱，柱腳轉(zhuǎn)角為零，而上端轉(zhuǎn)角不為零，故反彎點向上端移動鉸接：無約束作用，彎矩為零，自由轉(zhuǎn)動；固接：約束作用強，彎矩很大，轉(zhuǎn)角為零。InflectionPointMethod反彎點法Thehorizontalshearatamid-storeylevelofstoreyiissharedbetweenthecolumnsinproportiontotheshearrig