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

6.4AnalysisofRigidReinforcedConcreteFrameStructuresRigidFrameBehavior框架結構性能(a)Forcesanddeformationscausedbyexternalshear(b)Forcesanddeformationscausedbyexternalmoment框架總體剪切變形

框架總體彎曲變形

RigidFrameBehavior框架結構性能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.框架的側移忽略不計MomentsduetoverticalloadsaredeterminedwithsufficientaccuracybydividingtheentireframeintosimplesubframesApproximateDeterminationofMemberForcesCausedbyGravityLoading:FloorFrameSubstructureMethod分層力矩分配法Eachofsubframesconsistsofonecontinuousbeam,plusthetopandbottomcolumnsframingintothatparticularbeam.Thefarendsofthecolumnsareconsideredfixed柱端設為固定端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

1）對于現澆框架，要考慮梁有效截面慣性矩的調整；

2）柱端設為固定端；

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

4）梁和底層柱的傳遞系數(carry-overfactor)按遠端(farendsofmembers)固定，取1/2；上層各柱的傳遞系數取1/3。3.統(tǒng)計各層梁上豎向荷載(GravityLoading)設計值，并計算梁的固端彎矩(fixed-endmoment)。4.按前面規(guī)定的分配系數(distributionfactor)和傳遞系數(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抗側剛度(D0)atthatlevel.Theshearrigidityofacolumnislinearrigidityofcolumn

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