土木工程毕业设计外文翻译最终中英文.doc
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土木工程毕业设计外文翻译最终中英文.doc
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7Rigid-FrameStructures
Arigid-framehigh-risestructuretypicallycomprisesparallelororthogonallyarrangedbentsconsistingofcolumnsandgirderswithmomentresistantjoints.Resistancetohorizontalloadingisprovidedbythebendingresistanceofthecolumns,girders,andjoints.Thecontinuityoftheframealsocontributestoresistinggravityloading,byreducingthemomentsinthegirders.
Theadvantagesofarigidframearethesimplicityandconvenienceofitsrectangularform.Itsunobstructedarrangement,clearofbracingmembersandstructuralwalls,allowsfreedominternallyforthelayoutandexternallyforthefenestration.Rigidframesareconsideredeconomicalforbuildingsofupto'about25stories,abovewhichtheirdriftresistanceiscostlytocontrol.If,however,arigidframeiscombinedwithshearwallsorcores,theresultingstructureisverymuchstiffersothatitsheightpotentialmayextendupto50storiesormore.Aflatplatestructureisverysimilartoarigidframe,butwithslabsreplacingthegirdersAswitharigidframe,horizontalandverticalloadingsareresistedinaflatplatestructurebytheflexuralcontinuitybetweentheverticalandhorizontalcomponents.
Ashighlyredundantstructures,rigidframesaredesignedinitiallyonthebasisofapproximateanalyses,afterwhichmorerigorousanalysesandcheckscanbemade.Theproceduremaytypicallyincludethefollowingstages:
1.Estimationofgravityloadforcesingirdersandcolumnsbyapproximatemethod.
2.Preliminaryestimateofmembersizesbasedongravityloadforceswitharbitraryincreaseinsizestoallowforhorizontalloading.
3.Approximateallocationofhorizontalloadingtobentsandpreliminaryanalysisofmemberforcesinbents.
4.Checkondriftandadjustmentofmembersizesifnecessary.
5.Checkonstrengthofmembersforworstcombinationofgravityandhorizontalloading,andadjustmentofmembersizesifnecessary.
6.Computeranalysisoftotalstructureformoreaccuratecheckonmemberstrengthsanddrift,withfurtheradjustmentofsizeswhererequired.Thisstagemayincludethesecond-orderP-Deltaeffectsofgravityloadingonthememberforcesanddrift..
7.Detaileddesignofmembersandconnections.
Thischapterconsidersmethodsofanalysisforthedeflectionsandforcesforbothgravityandhorizontalloading.Themethodsareincludedinroughlytheorderofthedesignprocedure,withapproximatemethodsinitiallyandcomputertechniqueslater.StabilityanalysesofrigidframesarediscussedinChapter16.
7.1RIGIDFRAMEBEHAVIOR
Thehorizontalstiffnessofarigidframeisgovernedmainlybythebendingresistanceofthegirders,thecolumns,andtheirconnections,and,inatallframe,bytheaxialrigidityofthecolumns.Theaccumulatedhorizontalshearaboveanystoryofarigidframeisresistedbyshearinthecolumnsofthatstory(Fig.7.1).Theshearcausesthestory-heightcolumnstobendindoublecurvaturewithpointsofcontraflexureatapproximatelymid-story-heightlevels.Themomentsappliedtoajointfromthecolumnsaboveandbelowareresistedbytheattachedgirders,whichalsobendindoublecurvature,withpointsofcontraflexureatapproximatelymid-span.Thesedeformationsofthecolumnsandgirdersallowrackingoftheframeandhorizontaldeflectionineachstory.Theoveralldeflectedshapeofarigidframestructureduetorackinghasashearconfigurationwithconcavityupwind,amaximuminclinationnearthebase,andaminimuminclinationatthetop,asshowninFig.7.1.
Theoverallmomentoftheexternalhorizontalloadisresistedineachstorylevelbythecoupleresultingfromtheaxialtensileandcompressiveforcesinthecolumnsonoppositesidesofthestructure(Fig.7.2).Theextensionandshorteningofthecolumnscauseoverallbendingandassociatedhorizontaldisplacementsofthestructure.Becauseofthecumulativerotationuptheheight,thestorydriftduetooverallbendingincreaseswithheight,whilethatduetorackingtendstodecrease.Consequentlythecontributiontostorydriftfromoverallbendingmay,in.theuppermoststories,exceedthatfromracking.Thecontributionofoverallbendingtothetotaldrift,however,willusuallynotexceed10%ofthatofracking,exceptinverytall,slender,,rigidframes.Thereforetheoveralldeflectedshapeofahigh-riserigidframeusuallyhasashearconfiguration.
Theresponseofarigidframetogravityloadingdiffersfromasimplyconnectedframeinthecontinuousbehaviorofthegirders.Negativemomentsareinducedadjacenttothecolumns,andpositivemomentsofusuallylessermagnitudeoccurinthemid-spanregions.Thecontinuityalsocausesthemaximumgirdermomentstobesensitivetothepatternofliveloading.Thismustbeconsideredwhenestimatingtheworstmomentconditions.Forexample,thegravityloadmaximumhoggingmomentad
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