土木工程畢業(yè)設(shè)計(jì)外文翻譯最終中英文

7Rigid-FrameStructuresArigid-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.StabilityanalysesofrigidframesarediscussedinChapter16.7.1RIGIDFRAMEBEHAVIORThehorizontalstiffnessofarigidframeisgovernedmainlybythebendingresistanceofthegirders,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,thegravityloadmaximumhoggingmomentadjacenttoanedgecolumnoccurswhenliveloadactsonlyontheedgespanandalternateotherspans,asforAinFig.7.3a.Themaximumhoggingmomentsadjacenttoaninteriorcolumnarecaused,however,whenliveloadactsonlyonthespansadjacenttothecolumn,asforBinFig.7.3b.Themaximummid-spansaggingmomentoccurswhenliveloadactsonthespanunderconsideration,andalternateotherspans,asforspansABandCDinFig.7.3a.Thedependenceofarigidframeonthemomentcapacityofthecolumnsforresistinghorizontalloadingusuallycausesthecolumnsofarigidframetobelargerthanthoseofthecorrespondingfullybracedsimplyconnectedframe.Ontheotherhand,whilegirdersinbracedframesaredesignedfortheirmid-spansaggingmoment,girdersinrigidframesaredesignedfortheend-of-spanresultanthoggingmoments,whichmaybeoflesservalue.Consequently,girdersinarigidframemaybesmallerthaninthecorrespondingbracedframe.Suchreductionsinsizealloweconomythroughthelowercostofthegirdersandpossiblereductionsinstoryheights.Thesebenefitsmaybeoffset,however,bythehighercostofthemorecomplexrigidconnections.7.2APPROXIMATEDETERMINATIONOFMEMBERFORCESCAUSEDBYGRAVITYLOADSIMGArigidframeisahighlyredundantstructure;consequently,anaccurateanalysiscanbemadeonlyafterthemembersizesareassigned.Initially,therefore,membersizesaredecidedonthebasisofapproximateforcesestimatedeitherbyconservativeformulasorbysimplifiedmethodsofanalysisthatareindependentofmemberproperties.Twoapproachesforestimatinggirderforcesduetogravityloadingaregivenhere.7.2.1GirderForces—CodeRecommendedValuesInrigidframeswithtwoormorespansinwhichthelongerofanytwoadjacentspansdoesnotexceedtheshorterbymorethan20%,andwheretheuniformlydistributeddesignliveloaddoesnotexceedthreetimesthedeadload,thegirdermomentandshearsmaybeestimatedfromTable7.1.ThissummarizestherecommendationsgivenintheUniformBuildingCode[7.1].Inothercasesaconventionalmomentdistributionortwo-cyclemomentdistributionanalysisshouldbemadeforalineofgirdersatafloorlevel.7.2.2Two-CycleMomentDistribution[7.2].Thisisaconciseformofmomentdistributionforestimatinggirdermomentsinacontinuousmultibayspan.ItismoreaccuratethantheformulasinTable7.1,especiallyforcasesofunequalspansandunequalloadingindifferentspans.Thefollowingisassumedfortheanalysis:1.Acounterclockwiserestrainingmomentontheendofagirderispositiveandaclockwisemomentisnegative.2.Theendsofthecolumnsatthefloorsaboveandbelowtheconsideredgirderarefixed.3.Intheabsenceofknownmembersizes,distributionfactorsateachjointaretakenequalto1/n,wherenisthenumberofmembersframingintothejointintheplaneoftheframe.Two-CycleMomentDistribution—WorkedExample.Themethodisdemonstratedbyaworkedexample.InFig,7.4,afour-spangirderAEfromarigid-framebentisshownwithitsloading.Thefixed-endmomentsineachspanarecalculatedfordeadloadingandtotalloadingusingtheformulasgiveninFig,7.5.ThemomentsaresummarizedinTable7.2.Thepurposeofthemomentdistributionistoestimateforeachsupportthemaximumgirdermomentsthatcanoccurasaresultofdeadloadingandpatternliveloading.Adifferentloadcombinationmustbeconsideredforthemaximummomentateachsupport,andadistributionmadeforeachcombination.ThefivedistributionsarepresentedseparatelyinTable7.3,andinacombinedforminTable7.4.DistributionsainTable7.3arefortheexteriorsupportsAandE.ForthemaximumhoggingmomentatA,totalloadingisappliedtospanABwithdeadloadingonlyonBC.Thefixed-endmomentsarewritteninrows1and2.Inthisdistributiononly.theresultingmomentatAisofinterest.Forthefirstcycle,jointBisbalancedwithacorrectingmomentof-<-867+315>/4=-U/4assignedtoMBAwhereUistheunbalancedmoment.Thisisnotrecorded,buthalfofit,<-U/4>/2,iscarriedovertoMAB.Thisisrecordedinrow3andthenaddedtothefixed-endmomentandtheresultrecordedinrow4.ThesecondcycleinvolvesthereleaseandbalanceofjointA.Theunbalancedmomentof936isbalancedbyadding-U/3=-936/3=-312toMBA<row5>,implicitlyaddingthesamemomenttothetwocolumnendsatA.Thiscompletesthesecondcycleofthedistribution.TheresultingmaximummomentatAisthengivenbytheadditionofrows4and5,936-312=624.ThedistributionforthemaximummomentatEfollowsasimilarprocedure.DistributionbinTable7.3isforthemaximummomentatB.ThemostsevereloadingpatternforthisiswithtotalloadingonspansABandBCanddeadloadonlyonCD.TheoperationsaresimilartothoseinDistributiona,exceptthattheTfirstcycleinvolvesbalancingthetwoadjacentjointsAandCwhilerecordingonlytheircarryovermomentstoB.Inthesecondcycle,Bisbalancedbyadding-<-1012+782>/4=58toeachsideofB.Theadditionofrows4and5thengivesthemaximumhoggingmomentsatB.Distributionscandd,forthemomentsatjointsCandD,followpatternssimilartoDistributionb.ThecompletesetofoperationscanbecombinedasinTable7.4byinitiallyrecordingateachjointthefixed-endmomentsforbothdeadandtotalloading.Thenthejoint,orjoints,adjacenttotheoneunderconsiderationarebalancedfortheappropriatecombinationofloading,andcarryovermomentsassigned.totheconsideredjointandrecorded.Thejointisthenbalancedtocompletethedistributionforthatsupport.MaximumMid-SpanMoments.Themostsevereloadingconditionforamaximummid-spansaggingmomentiswhentheconsideredspanandalternateotherspansandtotalloading.Aconcisemethodofobtainingthesevaluesmaybeincludedinthecombinedtwo-cycledistribution,asshowninTable7.5.Adoptingtheconventionthatsaggingmomentsatmid-spanarepositive,amid-spantotal;loadingmomentiscalculatedforthefixed-endconditionofeachspanandenteredinthemid-spancolumnofrow2.Thesemid-spanmomentsmustnowbecorrectedtoallowforrotationofthejoints.Thisisachievedbymultiplyingthecarryovermoment,row3,attheleft-handendofthespanby<1+0.5D.F.>/2,andthecarryovermomentattheright-handendby-<1+0.5D.F.>/2,whereD.F.istheappropriatedistributionfactor,andrecordingtheresultsinthemiddlecolumn.Forexample,thecarryovertothemid-spanofABfromA=[<1+0.5/3>/2]x69=40andfromB=-[<1+0.5/4>/2]x<-145>=82.Thesecorrectionmomentsarethenaddedtothefixed-endmid-spanmomenttogivethemaximummid-spansaggingmoment,thatis,733+40+82=8ColumnForcesThegravityloadaxialforceinacolumnisestimatedfromtheaccumulatedtributarydeadandlivefloorloadingabovethatlevel,withreductionsinliveloadingaspermittedbythelocalCodeofPractice.Thegravityloadmaximumcolumnmomentisestimatedbytakingthemaximumdifferenceoftheendmomentsintheconnectedgirdersandallocatingitequallybetweenthecolumnendsjustaboveandbelowthejoint.Tothisshouldbeaddedanyunbalancedmomentduetoeccentricityofthegirderconnectionsfromthecentroidofthecolumn,alsoallocatedequallybetweenthecolumnendsaboveandbelowthejoint.第七章框架結(jié)構(gòu)高層框架結(jié)構(gòu)一般由平行或正交布置的梁柱結(jié)構(gòu)組成,梁柱結(jié)構(gòu)是由帶有能承擔(dān)彎矩作用節(jié)點(diǎn)的梁、柱組成。具有抗彎能力的梁、柱和節(jié)點(diǎn)共同作用抵抗水平荷載。連續(xù)框架可降低梁的跨中彎矩而有利于抵抗重力荷載。框架結(jié)構(gòu)有簡(jiǎn)捷和便于采用矩形體系的優(yōu)點(diǎn)。由于這種布置形式?jīng)]有斜支撐和結(jié)構(gòu)墻體,因此,沒(méi)有不便利之處,部可以自由布置,外部可以自由設(shè)計(jì)門、窗。框架結(jié)構(gòu)對(duì)于25層以的建筑是經(jīng)濟(jì)的,超過(guò)25層由于要限制其位移而花費(fèi)的代價(jià)高,顯得很不經(jīng)濟(jì)。如果框架與剪力墻及芯筒相結(jié)合,剛度能夠大幅度提高,可以建造50層以上的建筑。板柱結(jié)構(gòu)與框架結(jié)構(gòu)非常相似,不同之處僅是用板代替了梁。和框架結(jié)構(gòu)一樣,板柱結(jié)構(gòu)是通過(guò)其水平和豎向構(gòu)件之間的連續(xù)抗彎作用來(lái)抵抗水平和豎向荷載。對(duì)于高次超靜定框架結(jié)構(gòu),應(yīng)根據(jù)近似分析進(jìn)行初步設(shè)計(jì),隨后進(jìn)行精確分析和校核。分析過(guò)程一般包括以下幾步:1．按近似方法確定梁和柱所受重力荷載;2．初步確定在重力荷載作用下構(gòu)件的截面尺寸,考慮水平荷載的作用進(jìn)行構(gòu)件截面尺寸的任意調(diào)整;3．將水平荷載分配到各梁柱結(jié)構(gòu)上,對(duì)這些結(jié)構(gòu)構(gòu)件的力進(jìn)行初步分析;4．檢驗(yàn)位移并對(duì)構(gòu)件截面尺寸做必要的調(diào)整;5．按最不利的重力荷載和水平荷載組合檢驗(yàn)構(gòu)件強(qiáng)度,做必要的構(gòu)件截面尺寸調(diào)整;6．為了更精確地驗(yàn)算構(gòu)件強(qiáng)度和位移,利用計(jì)算機(jī)對(duì)結(jié)構(gòu)進(jìn)行整體分析,需要時(shí)則近一步調(diào)整構(gòu)件截面尺寸。這一階段中應(yīng)包括考慮重力荷載對(duì)構(gòu)件力和位移產(chǎn)生的Ρ一△二階效應(yīng);7．構(gòu)件和節(jié)點(diǎn)的詳細(xì)設(shè)計(jì)。本章討論在重力和水平荷載作用下結(jié)構(gòu)的變形和力分析方法。這些方法基本上按照設(shè)計(jì)過(guò)程中的次序介紹,首先是近似法,然后介紹計(jì)算機(jī)分析技術(shù)?？蚣芙Y(jié)構(gòu)的穩(wěn)定性分析將在第十六章中討論。7.1框架結(jié)構(gòu)的性能框架結(jié)構(gòu)的側(cè)向剛度主要取決于梁、柱及節(jié)點(diǎn)的抗彎能力,在較高的框架中主要取決于柱子的軸向剛度。作用于框架任一層間的水平集中剪力由該層柱子的抗剪能力抵抗<圖7.1>。剪力使框架結(jié)構(gòu)每層的柱產(chǎn)生雙曲率彎曲,其反彎點(diǎn)大約在層高的中間部位。上、下柱引起的作用于節(jié)點(diǎn)處的彎矩由相鄰梁承擔(dān),該梁、柱的變形引起框架的整體變形,使各層間產(chǎn)生水平位移。在水平推力作用下結(jié)構(gòu)的整體變形和剪力圖如圖7.1所示,其凹面朝向風(fēng)荷載作用方向,最大傾角在基底附近,最小傾角在頂端。外部水平荷載產(chǎn)生的總彎矩由各層間兩個(gè)邊柱中的軸向拉、壓力組成的力矩抵抗<圖7.2>。柱子的伸、縮引起結(jié)構(gòu)的整體彎曲變形,并產(chǎn)生相應(yīng)的水平位移。因?yàn)檗D(zhuǎn)角沿建筑高度累加,所以整體彎曲變形引起的層間位移隨高度增加而增加,而剪切變形引起的層間位移隨高度的增加而減小。其結(jié)果在建筑的最頂部整體彎曲對(duì)層間位移的貢獻(xiàn)會(huì)大大超過(guò)剪切變形對(duì)層間位移的貢獻(xiàn)。但是,整體彎曲變形對(duì)總位移的貢獻(xiàn)與剪切變形對(duì)總位移的貢獻(xiàn)之比不會(huì)超過(guò)10％,除非在極高或細(xì)長(zhǎng)的框架中。因此,高層框架結(jié)構(gòu)變形型式為剪切型。從梁的連接受力性能來(lái)看,高層建筑采用的剛性節(jié)點(diǎn)連續(xù)的框架不同于一般簡(jiǎn)單連接的普通框架。梁在柱邊附近產(chǎn)生負(fù)彎矩,跨中正彎矩值常常很小。這種連續(xù)性能使梁中最大彎矩對(duì)活荷載的作用方式非常敏感。如果能夠估計(jì)出產(chǎn)生最不利彎矩的因素,則必須加以認(rèn)真的考慮。例如,重力荷載作用下梁在邊柱附近產(chǎn)生的最大負(fù)彎矩只會(huì)在活荷載作用于邊跨和相間跨時(shí)才能發(fā)生,如圖7.3a中的A點(diǎn)。而梁在柱附近產(chǎn)生的最大負(fù)彎矩只會(huì)在活荷載作用于相鄰跨時(shí)才能發(fā)生,如圖7.3a中的B點(diǎn)。當(dāng)活荷載作用于本跨和相間跨時(shí),梁的跨中正彎矩最大,如圖7.3a中的AB和CD跨。框架的尺寸取決于柱子在水平荷載作用·下的抗彎強(qiáng)度,這往往會(huì)使框架柱的截面尺寸大于相應(yīng)全對(duì)角支撐簡(jiǎn)單連接框架的柱截面尺寸。另外,框架支撐結(jié)構(gòu)中的梁被設(shè)計(jì)為只具有跨中正彎矩,而框架結(jié)構(gòu)的梁則被設(shè)計(jì)為端部為負(fù)彎矩和跨中為正彎矩,跨中彎矩值較小。因此,框架結(jié)構(gòu)中梁的截面尺寸會(huì)小于相應(yīng)的框架支撐結(jié)構(gòu)中梁的截面尺寸。梁截面的減小將會(huì)降低其造價(jià),有時(shí)可以降低層高,經(jīng)濟(jì)效益明顯。但是,由于剛性節(jié)點(diǎn)的處理相當(dāng)復(fù)雜,代價(jià)較高,使上述經(jīng)濟(jì)優(yōu)勢(shì)被削弱。7.2重力荷載作用下構(gòu)件力的近似計(jì)算框架結(jié)構(gòu)是多次超靜定結(jié)構(gòu),因此,只有在確定了構(gòu)件截面尺寸后才能進(jìn)行精確分析。所以,在初步設(shè)計(jì)階段,可根據(jù)傳統(tǒng)的公式和不考慮構(gòu)件特征值的簡(jiǎn)化分析法近似確定構(gòu)件中的力,以此為基礎(chǔ)確定構(gòu)件的截面尺寸。下面將討論在重力荷載作用下構(gòu)件力計(jì)算的兩種方法。7.2.1梁的力—規(guī)推薦值對(duì)于兩跨以上的框架結(jié)構(gòu),當(dāng)任何相鄰兩跨中的長(zhǎng)跨不超過(guò)短跨的20%跨度,同時(shí)設(shè)計(jì)均布活荷載不超過(guò)3倍的恒載時(shí),梁的彎矩和剪力可以按表7.1確定。表中各數(shù)值是根據(jù)統(tǒng)筑規(guī)[7.1]中的推薦值給出。對(duì)于其它情況,可按照樓面連續(xù)梁采月傳統(tǒng)彎矩分配法或兩次循環(huán)彎矩分配法進(jìn)行分析確定。7.2.2彎