大型橋梁及施工外文翻譯-大跨度橋梁

大型橋梁及施工外文翻譯--大跨度橋梁1LargeSpanBridgeSuspensionBridgeThesuspensionbridgeiscurrentlytheonlysolutioninexcessof600m,andisregardedascompetitivefordownto300.Theworld’slongestbridgeatpresentistheVerrazanoNarrowsbridgeinNewYork.AnothermodernexampleistheSevernBridgeinEngland.Thecomponentsofasuspensionbridgeare:(a)flexiblecables,(b)towers,(c)anchorages,(d)suspenders,(e)deckand，(f)stiffeningtrusses.Thecablenormallyconsistsofparallelwiresofhightensilesteelindividuallyspunatsiteandboundintooneunit.Eachwireisgalvanizedandthecableiscoverwithaprotectivecoating.Thewireforthecableshouldbecold-drawnandnotoftheheat-treatedvariety.Specialattentionshouldbepaidtoaestheticsinthedesignoftherowers.Thetowerishighandisflexibleenoughtopermittheiranalysisashingedatbothends.Thecableisanchoredsecurelyanchoredtoverysolidanchorageblocksatbothends.Thesuspenderstransfertheloadformthedecktothecable.Theyaremadeupofhightensilewiresandarenormallyvertical.Thedeckisusuallyorthotropicwithstiffenedsteelplate,ribsortroughs，floorbeam,etc.Stiffeningtrusses,pinnedatthetowers,areproviding.Thestiffeningsystemservestocontrolaerodynamicmovementsandtolimitthelocalanglechangesinthedeck.Ifthestiffeningsystemisinadequate,torsionaloscillationsduetowindmightresultinthecollapseofthestructure,asillustratedinthetragicfailurein1940ofthefirstTacomaNarrowsThesidespantomainspanratiovariesfrom0.17to0.50.Thespantodepthratioforthestiffeningtrussinexistingbridgeliesbetween85and100forspansupto1,000mandrisesrathersteeplyto177.Theratioofspantowidthofdeckforexistingbridgesrangesfrom20to56.Theaerodynamicstabilitywillhavebetobeinvestigatedthoroughlybydetailedanalysisaswellaswindtunneltestsonmodels.Thecable-stayedbridgeDuringthepastdecadecable-stayedbridgeshavefoundwideapplication,s\especiallyinWesternEurope,andtoalesserextentinotherpartsoftheworld.Therenewalofthecable-stayedsysteminmodernbridgeengineeringwasduetothetendencyofbridgeengineeringinEurope,primarilyGermany,toobtainoptimumstructuralperformancefrommaterialwhichwasinshortsupply-duringthepost-waryears.大型橋梁及施工外文翻譯--大跨度橋梁全文共1頁，當(dāng)前為第1頁。Cable-stayedbridgesareconstructedalongastructuralsystemwhichcomprisesanorthotropicdeckandcontinuousgirderswhicharesupportedbystays,i.e.inclinedcablespassingoverorattachedtotowerslocatedatthemainpiers.大型橋梁及施工外文翻譯--大跨度橋梁全文共1頁，當(dāng)前為第1頁。Theideaofusingcablestosupportbridgespanbridgespanisbynomeansnew,andanumberofexamplesofthistypeofconstructionwererecordedalongtimeago.Unfortunatelythesystemingeneralmetwithlittlesuccess,duetothefactthatthestaticswerenotfullyunderstoodandthatunsuitablematerialssuchasbarsandchainswereusedtoformtheinclinedsupportsorstays.Staysmadeinthismannercouldnotbefullytensionedandinaslackconditionallowedlargedeformationsofthedeckbeforetheycouldparticipateintakingthetensileloadsforwhichtheywereintended.Wideandsuccessfulapplicationofcable-stayedsystemswasrealizedonlyrecently,withtheintroductionofhigh-strengthsteels,orthotropicdecks,developmentofweldingtechniquesandprogressinstructuralanalysis.Thedevelopmentandapplicationofelectroniccomputersopenedupnewandpracticallyunlimitedpossibilitiesforexactsolutionofthesehighlystaticallyindeterminatesystemsandforprecisestoicalanalysisoftheirthree-dimensionalperformance.Existingcable-stayedbridgesprovideusefuldataregardingdesign,fabrication,erectionandmaintenanceofthemewsystem.Withtheconstructionofthesebridgesmanybasicproblemsencounteredintheirengineeringareshowntohavebeensuccessfullysolved.However,theseimportantdatahaveapparentlyneverbeforebeensystematicallypresented.Theapplicationofinclinedcablegaveanewstimulustoconstructionoflargebridges.Theimportanceofcable-stayedbridgesincreasedrapidlyandwithinonlyonedecadetheyhavebecomesosuccessfulthattheyhavetakentheirrightfulplaceamongclassicalbridgesystem.Itisinterestingtonotenowhowthisdevelopmentwhichhassorevolutionizedbridgeconstruction,butwhichinfactisnonewdiscovery,cameabout.Thebeginningofthissystem,probably,maybetracedbacktothetimewhenitwasrealizedthatrigidstructurescouldbeformedbyjoiningtrianglestogether.Althoughmostoftheseearlierdesignswerebasedonsoundprinciplesandassumptions,thegirderstiffenedbyinclinedcablessufferedvariousmisfortuneswhichregrettablyresultedinabandonmentofthesystem.Nevertheless,thesysteminitselfwasnotatallunsuitable.Thesolutionoftheproblemhadunfortunatelybeenattemptedinthewrongway.大型橋梁及施工外文翻譯--大跨度橋梁全文共2頁，當(dāng)前為第2頁。Therenaissanceofthecable-stayed,however,wasfinallysuccessfullyachievedonlyduringthelastdecade.大型橋梁及施工外文翻譯--大跨度橋梁全文共2頁，當(dāng)前為第2頁。Moderncable-stayedpresentathree-dimensionalsystemconsistingofstiffeninggirders,transverseandlongitudinalbracings,orthotropic-typedeckandsupportingpartssuchastowersincompressionandinclinedcablesintension.Theimportantcharacteristicsofsuchathree-dimensionalstructureisthefullparticipationofthetransverseconstructionintheworkofthemainlongitudinalstructure.Thismeansaconsiderableincreaseinthemomentofinertiaoftheconstructionwhichpermitsareductioninthedepthofthegirdersandeconomyinsteel.Longspanconcretebridgesareusuallyofpost-tensionedconcreteandconstructedeitherasconditionsbeamstypesorasfreeversatilestructures.Manymethodshavebeendevelopedforcontinuousdeckconstruction.Iftheclearancebetweenthegroundandbottomofthedeckissmallandthesoilisfirm,thesuperstructurecanbebuiltonstaging.Thismethodisbecomingobsolete.Currently,free-cantileverandmovablescaffoldsystemsareincreasinglyusedtosavetimeandimprovesafety.Themovablescaffoldsystememploysmovableformsstiffenedbysteelframes.Theseformsextendonespanlengthandaresupportedbysteelgirderswhichrestonapieratoneendandcanbemovedfromspantospanonasecondsetofauxiliarysteelgirders.Aneconomicalconstructiontechniqueknownasincrementalpush-launchingmethodisdevelopedbyBaur-Leonhardteam.Thetotalcontinuousdeckissubdividedlongitudinallyintosegmentsof10to30mlengthdependingonthelengthofspansandthetimeavailableforconstruction.Eachofthesesegmentsisconstructedimmediatelybehindtheabutmentofthebridgeinsteelframedforms,whichremaininthesameplaceforconcretingallsegments.Theformsaresodesignedastobecapableofbeingmovedtransverselyorrotatedonhingestofacilitateeasystrippingaftersufficienthardeningofconcrete.Attheheadofthefirstsegment,asteelnoseconsistingofalighttrussisattachedtofacilitatereachingofthefirstandsubsequentpierswithoutincludingatoolargecanyieldermomentduringconstruction.Thesecondandthefollowingsegmentsareconcreteddirectlyonthefaceofthehardenedportionandthelongitudinalreinforcementcancontinueacrosstheconstructionjoint.Thepushingisachievedbyhydraulicjackswhichactagainsttheabutment.SincethecoefficientoffrictionofTeflonslidingbearingsisonlyabout2percent,lowcapacityhydraulicjackswouldsufficetomovethebridgeevenoverlonglengthsofseveralhundredmetres.Thismethodcanbeusedforstraightandcontinuouslycurvedbridgesuptoaspanofabout120m.大型橋梁及施工外文翻譯--大跨度橋梁全文共3頁，當(dāng)前為第3頁。Thefree-cantileversystemwaspioneeredbyDyckerhoffandWillmanninGermany.Inthissystem,thesuperstructureiserectedbymeansofcantilevertruckinsectionsgenerallyof3.5m.Thecantilevertruck,whosecostisrelativelysmallandwhichisattachedfirmlytopermanentconstruction,emitsbyrepeatedusetheconstructionoflargebridges.Theavoidanceofscaffoldfrombelow,thespeedofworkandthesavinginlaborcostresultintheconstructionbeingveryeconomical.Thefree-cantileversystemisideallysuitedforlaunchedgirderswithalargedepthabovethepiercantileversystemisideallysuitedforlaunchedgirderswithalargedepthabovethepiercantileveringtothemiddleofthespan.大型橋梁及施工外文翻譯--大跨度橋梁全文共3頁，當(dāng)前為第3頁。Anothertechniqueistheuseofthepneumaticcaisson.Thecaissonisahugecylinderwithabottomedgethatcancutintothewaterbed.Whencompressedispumpedintoit,thewaterisforcedout.Caissonsmustbeusedwithextremecare.foronething,workerscanonlystayinthecompressionchamberforshortperiodsoftime.Foranother,iftheycomeuptonormalatmosphericpressuretoorapidly,theyaresubjecttothebends,orcaissondiseaseasitisalsocalled,whichisacripplingorevenfatalconditioncausedbyexcessnitrogenintheblood.WhentheEadsBridgeacrosstheMississippiRiveratSt.Louiswasunderconstructionbetween1867and1874,atatimewhenthedangerofworkingincompressedairwasnotfullyunderstood,fourteendeathswascausedbythebends.Whenextrastrengthisnecessaryinthepiers,theysometimeskeyedintothebedrock-thatis,theyareextendeddownintothebedrock.ThismethodwasusedtobuildthepiersfortheGoldenGateBridgeinSanFrancisco,whichissubjecttostrongtidiesandhighwinds,andislocatedinanearthquakezone.Thedrillingwascarriedoutunderwaterbydeep-seadivers.Wherebedrockcannotbereached,pilesaredrivenintothewaterbed.Today,thepilesinconstructionareusuallymadeofprestressedconcretebeams.Oneingenioustechnique,usedfortheTappanZeeBridgeacrosstheHudsonRiverinNewYork,istorestahollowconcreteboxontopofalayerofpiles.Whentheboxispumpeddry,itbecomesbuoyantenoughtosupportalargeproportionoftheweightofthebridge.Eachtypeofbridgeindeedeachindividualbridgepresentsspecialconstructionproblems.Withsometrussbridges,thespanisfloatedintopositionafterthepiershavebeenerectedandthenraisedintoplacebymeansofjacksorcranes.Archbridgescanbeconstructedoverafalsework,ortemporaryscaffolding.Thismethodisusuallyemployedwithreinforcedconcretearchbridges.Withsteelarches,however,atechniquehasbeendevelopedwherebythefinishedsectionsareheldinplacebywiresthatsupplyacantileversupport.Cranesmovealongthetopofthearchtoplacenewsectionsofsteelwhilethetensioninthecablesincreases.大型橋梁及施工外文翻譯--大跨度橋梁全文共4頁，當(dāng)前為第4頁。Withsuspensionbridges,thefoundationsandthetowersarebuiltfirst.Thenacableisrunfromtheanchorage-concreteblockinwhichthecableisfastened-uptothetowerandacrosstotheoppositetowerandanchorage.Awheelthatunwindswirefromareelpunsalongthiscable.Whenthereelreachestheotherside,anotherwireisplacedonit,andthewheelreturnstoitsoriginalposition.Whenallthewireshavebeenputinplace,anothermachinemovesalongthecabletocompactandtobindthem.Constructionbeginsonthedeckwhenthecablesareinplace,withworkprogressingtowardthemiddlefromeachendofthestructure.大型橋梁及施工外文翻譯--大跨度橋梁全文共4頁，當(dāng)前為第4頁。Theloadstobeconsideredinthedesignofsubstructuresandbridgefoundationsincludeloadsandforcestransmittedfromthesuperstructure,andthoseactingdirectlyonthesubstructureandfoundation.AASHTOloads.Section3ofAASHTOspecificationssummarizestheloadsandforcestobeconsideredinthedesignofbridges(superstructureandsubstructure).Briefly,thesearedeadload,liveload,impactordynamiceffectofliveload,windload,andotherforcessuchaslongitudinalforces,centrifugalforce,thermalforces,earthpressure,buoyancy,shrinkageandlongtermcreep,ribshortening,erectionstresses,iceandcurrentpressure,collisionforce,andearthquakestresses.Besidestheseconventionalloadsthataregenerallyquantified,AASHTOalsorecognizesindirectloadeffectssuchasfrictionatexpansionbearingsandstressesassociatedwithdifferentialsettlementofbridgecomponents.TheLRFDspecificationsdivideloadsintotwodistinctcategories:permanentandtransient.大型橋梁及施工外文翻譯--大跨度橋梁全文共5頁，當(dāng)前為第5頁。大型橋梁及施工外文翻譯--大跨度橋梁全文共5頁，當(dāng)前為第5頁。大跨度橋梁懸索橋懸索橋是現(xiàn)行的跨徑超過600m大橋的唯一解決方案，而且對跨徑在300m以上的橋梁它也是被認(rèn)為是一種很有競爭力的方案?，F(xiàn)在世界上最大跨徑的橋梁是紐約的威拉查諾（Verrazano）海峽大橋，另一個(gè)是英國的塞溫（Savern）大橋。懸索橋的組成部分有：柔性，主塔，錨碇，吊索（掛索），橋面板和加勁桁架。主纜是有一組平行的單根高強(qiáng)鋼絲在現(xiàn)場扭在一起并綁扎成型的鋼絲束組成的。每根鋼絲都是經(jīng)過渡鋅處理的，并且整個(gè)用保護(hù)層覆蓋著。所用的鋼絲應(yīng)該是冷拔鋼絲而不是經(jīng)過熱處理的各種鋼絲。在進(jìn)行主塔設(shè)計(jì)時(shí)應(yīng)該特別注意其在美學(xué)上的要求。主塔很高而且具有足夠的柔性，使其每一座塔頂都可認(rèn)為是與主纜鉸接。主纜的兩端很安全的錨固在非常堅(jiān)實(shí)的錨碇上。吊索把橋面板上的荷載傳遞到主主纜上。吊索也是有高強(qiáng)鋼絲制成的而且通常是豎直的。橋面板通常是有加勁鋼板，肋或槽型板，橫梁制成的異性結(jié)構(gòu)。提供一些加勁梁連接在其主塔之間，能夠起到控制空氣動(dòng)力運(yùn)動(dòng)并限制橋面板局部傾角變化。如果加勁系統(tǒng)不適當(dāng)，由于風(fēng)引起的豎向振動(dòng)也許會(huì)導(dǎo)致結(jié)構(gòu)傾斜，就像塔科瑪（Tacoma）海峽大橋的悲劇性的破壞所表明的那樣。邊跨與主跨的跨徑比的變化范圍是0.17~0.50。在現(xiàn)有的采用加勁梁的橋梁上，當(dāng)跨徑高大1000米時(shí)跨徑與橋梁的建筑高度之比為85與100之間?，F(xiàn)有的橋梁的跨徑與橋面板寬度之比約為20~56。橋梁結(jié)構(gòu)的空氣動(dòng)力穩(wěn)定性必須得通過對其模型的風(fēng)洞試驗(yàn)及細(xì)部分析進(jìn)行全面的研究。斜拉橋體系在過去的十年間，斜拉橋得以廣泛的應(yīng)用，尤其實(shí)在歐洲，而在世界其它地區(qū)，應(yīng)用相對少一些。在現(xiàn)代橋梁工程中，斜拉橋體系的重新興旺起來是由于歐洲（主要是德國）的橋梁工程師有一種趨勢，即從因?yàn)閼?zhàn)爭而短缺的材料上獲得最佳的結(jié)構(gòu)性能。斜拉橋是有按各向異性橋面板和由吊索支撐的連續(xù)梁構(gòu)成的體系建造起來的，這些吊索是一些穿過或固定的位于主橋墩的索塔頂上的傾斜主纜。大型橋梁及施工外文翻譯--大跨度橋梁全文共6頁，當(dāng)前為第6頁。用主纜來支撐橋跨并不是一種新思想，在很早以前就有大量此類結(jié)構(gòu)的的記載。不幸的是這一體系只有很少成功的例子，這是由于人們對靜力學(xué)的原理沒有完全弄明白，并且還沒有構(gòu)成傾斜支撐或吊索的適當(dāng)?shù)牟牧?，例如主纜和鋼鏈等。這種吊索在它們能夠按計(jì)劃承擔(dān)拉力之前不能完全被拉緊，而應(yīng)處于允許橋面板產(chǎn)生較大變形的松弛狀態(tài)。大型橋梁及施工外文翻譯--大跨度橋梁全文共6頁，當(dāng)前為第6頁。斜拉體系的廣泛的成功的應(yīng)用只在近年來，隨著高強(qiáng)鋼，各種異性橋面板的引入、焊接技術(shù)的發(fā)展和結(jié)構(gòu)分析方法的進(jìn)步才得以實(shí)現(xiàn)。電子計(jì)算機(jī)的發(fā)展和應(yīng)用，導(dǎo)致了解決高次超靜定體系的精確值及它們的三維空間性能的精確靜力分析的新的無實(shí)際限制的可能性?，F(xiàn)有的斜拉橋提供了許多關(guān)于設(shè)計(jì)、制造、安裝和維修的有用的數(shù)據(jù)。隨著這些橋梁的建造，許多工程中遇到的基本問題已表明的到了成功的解決。然而這些重要的數(shù)據(jù)很顯然在這以前決沒有被系統(tǒng)的揭示出來。斜吊索的應(yīng)用對大型橋梁建造帶來了一個(gè)新刺激。斜拉橋的重要性迅速增加起來，并且在僅三十年間這種橋梁類型就變的這樣成功，已使其在古典橋梁體系中取得了它應(yīng)有的地位。如果我們注意到這種橋梁建造帶來如此徹底的變革的發(fā)展是怎樣發(fā)生的話，我們都會(huì)感興趣的，因?yàn)檫@一發(fā)展事實(shí)上并沒有什么任何新發(fā)現(xiàn)。這一體系的開始也許可以追溯到人們開始認(rèn)識(shí)到通過三角形連接在一起能夠構(gòu)成剛性結(jié)構(gòu)的時(shí)代。盡管大多數(shù)這種設(shè)計(jì)是基于結(jié)構(gòu)堅(jiān)固的原理和假定的，但斜拉加勁梁還是遭受各種各樣的不幸事故，而最終令人遺憾的導(dǎo)致了這一體系被放棄。盡管這樣，這一體系并不是完全不適應(yīng)，只是問題的解決被不幸的應(yīng)用錯(cuò)誤的方式去嘗試。然而，斜拉體系的復(fù)興只是在近十年來才最終獲得成功?，F(xiàn)代的斜拉橋提出了加勁梁、橫向及縱向聯(lián)系梁、各項(xiàng)異性橋面板和支撐部分（例如處于受壓狀態(tài)的索塔及受拉狀態(tài)的斜吊索）組成的三維空間體系。象這種空間三維結(jié)構(gòu)的重要特征是橫向結(jié)構(gòu)全部參與主要縱向結(jié)構(gòu)的工作狀態(tài)。這就意味著結(jié)構(gòu)的慣性矩大大增加，這使的橋的建筑高度可以減少，并且使用鋼材是最經(jīng)濟(jì)的。大跨度橋梁經(jīng)常是連續(xù)梁形式或懸臂梁形式的預(yù)應(yīng)力混凝土橋梁。以前許多的施工方法已發(fā)展為連續(xù)梁橋的施工方法。如果模板和地面之間的距離較小并且土質(zhì)堅(jiān)硬，橋梁的上部結(jié)構(gòu)可以使用支架施工方法。不過這種施工方法已經(jīng)越來越過時(shí)了。目前，自由懸臂法和移動(dòng)模架法的應(yīng)用漸廣并能節(jié)省時(shí)間和提高安全性。移動(dòng)模架法是利用固定在鋼制臺(tái)架上的移動(dòng)系統(tǒng)而形成，這種系統(tǒng)能夠達(dá)到一跨長并支承在一端支承在橋墩上并借助于第二根鋼導(dǎo)梁逐跨移動(dòng)的鋼梁上。大型橋梁及施工外文翻譯--大跨度橋梁全文共7頁，當(dāng)前為第7頁。一種經(jīng)濟(jì)的施工方法是被廣泛知曉的由Baur-leonhard團(tuán)隊(duì)所發(fā)展的使用廣泛的頂推法。整個(gè)的連續(xù)梁被劃分成10-30米長度的節(jié)段，這種劃分主要依據(jù)跨徑和能夠利用的施工時(shí)間。每個(gè)節(jié)段在橋臺(tái)后面的鋼模上能夠快速澆注，鋼?？梢灾苻D(zhuǎn)使用而澆注所有的節(jié)段。這樣設(shè)計(jì)模板是為了能夠橫向移動(dòng)或在鉸上轉(zhuǎn)動(dòng)，以便在混凝土充分硬化后脫模。在第一節(jié)段的頂端安裝上一個(gè)由輕型桁架組成的鋼導(dǎo)梁，以實(shí)現(xiàn)第一節(jié)段