土木工程建筑外文翻譯外文文獻(xiàn)英文文獻(xiàn)橋梁施工方法

橋梁施工方法一座橋梁的最終造價(jià)是建造橋梁結(jié)構(gòu)物的材料費(fèi)用與這項(xiàng)工程相關(guān)的機(jī)械費(fèi)用和臨時(shí)工程及勞動(dòng)力的費(fèi)用的總和。材料的費(fèi)用能夠被預(yù)算的相當(dāng)準(zhǔn)確的，承包商們借助施工經(jīng)驗(yàn)是能夠估算施工機(jī)械和勞動(dòng)力的費(fèi)用的。但是勞動(dòng)力的費(fèi)用是不能夠精確分析的。最近的一項(xiàng)比較有競(jìng)爭(zhēng)力的設(shè)計(jì)試圖通過減少臨時(shí)工程和工程的工期來革新施工方法。橋梁上部結(jié)構(gòu)比較適宜的施工方法將隨施工場(chǎng)地不同而不同，并主要取決于橋梁的長(zhǎng)度和跨度、橋梁的類型、基礎(chǔ)條件及其所使用的材料。例如：現(xiàn)場(chǎng)澆注混凝土的施工方法適用于40米以下的短跨徑橋梁，如果河床在一年中的大部分時(shí)間是干燥的，那么預(yù)應(yīng)力混凝土懸臂施工方法在有通航要求的大跨橋梁中是比較合適的。現(xiàn)在的發(fā)展趨勢(shì)是盡可能避免使用臺(tái)架施工，而在最大程度上采用預(yù)制構(gòu)件；另一方面，起重機(jī)、滑拽梁等施工機(jī)械的應(yīng)用范圍也越來越廣。這些都是從對(duì)施工方法的密切關(guān)注甚至是設(shè)計(jì)過程的密切關(guān)注而取得的巨大收獲，而不是在善于解決永久材料。小跨度橋梁當(dāng)橋梁的跨度小于40米左右時(shí)，它的上部結(jié)構(gòu)可以通過支承在地面上的趾甲施工。其它的施工方法中的梁可以整體預(yù)制，然后利用頂推梁或起重機(jī)架設(shè)。如果這座橋梁是等跨的，在后一種施工方法中，由于架設(shè)設(shè)備而增加的費(fèi)用和由于施工工期短而減少的費(fèi)用之和將會(huì)比前一種施工方法的模板制作費(fèi)用低。大跨度橋梁大跨度橋梁經(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(zhǎng)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。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(zhǎng)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)段以后的節(jié)段順利架設(shè)而防止在施工出現(xiàn)過大的懸臂部分。第二節(jié)段及以后的節(jié)段可以直接在第一節(jié)段的硬化面上澆注并在施工過程中將節(jié)段連接起來。頂推是通過支承在橋臺(tái)上的液壓千斤頂實(shí)現(xiàn)的，由于聚四氟乙烯的滑塊的摩擦系數(shù)只有 0.02，低效能的千斤頂就足夠完成長(zhǎng)度甚至達(dá)數(shù)百米的橋梁的頂推。這種方法可以應(yīng)用在長(zhǎng)度在 120米左右的直線橋梁或曲線橋梁上。自由懸臂法是由法國(guó)的Dyckerhoff和Willmann所創(chuàng)始。這種施工方法中，橋梁的上部結(jié)構(gòu)是通過節(jié)段長(zhǎng)度基本在3.5米的懸臂機(jī)上施工，懸臂機(jī)的費(fèi)用相對(duì)比較低并且固定在橋梁承重結(jié)構(gòu)上，由于它的重復(fù)利用性使它能在長(zhǎng)橋上使用。由于施工速度的加快和時(shí)間的節(jié)省使得這種施工方法的費(fèi)用比較低從而避免了使用臺(tái)架施工，自由懸臂法比較適用于橋墩較高并且懸臂能伸到跨徑中部的橋梁上。另一種施工方法是整體沉箱法。沉箱是一種底邊有刃腳的大型圓筒，其刃腳可以切入水底。當(dāng)壓縮空氣進(jìn)入沉箱內(nèi)部時(shí)水就會(huì)被排出。沉箱的利用必須嚴(yán)加注意。首先，工人們只能在這種壓縮空氣的空間里呆很短的時(shí)間；另一方面，如果工人們從沉箱進(jìn)入正常的大氣壓條件下過于迅速，他們將比較容易患上潛水?。ㄒ脖环Q作沉箱病） ，這在能使人致殘的甚至致命的環(huán)境中由于血液中氧氣過多所引起的一種病。當(dāng)St.louis市的密西西比河 Eads上的橋在1867-1874年施工時(shí)，由于人們對(duì)在壓縮空氣中工作的危險(xiǎn)性認(rèn)識(shí)不足，最后由于患潛水病而導(dǎo)致 14人死亡。當(dāng)在橋墩上有外力作用時(shí)，基樁經(jīng)常需要嵌入基巖，也就是說它們的下部一直延伸到基巖。這種方法曾經(jīng)用來建造位于強(qiáng)風(fēng)和地震區(qū)域的舊金山金門大橋的橋墩。鉆孔是在水下由深水潛水員進(jìn)行的。在不能到達(dá)基巖的地方，樁通常被打進(jìn)河床。今天，在施工的基樁基本上是預(yù)應(yīng)力混凝土結(jié)構(gòu)。在建造紐約哈德遜河上的泰平.吉橋時(shí)所采用的一種巧妙技術(shù)是將一個(gè)空心混凝土箱置于橋樁層上，當(dāng)它里面的水被抽干時(shí)，它的浮力足夠支承橋梁重力的一大部分。每一種類型的橋梁實(shí)際上代表了特殊的問題。許多桁架橋的施工是先將橋上桁架運(yùn)到已施工完畢的基樁位置，然后再利用千斤頂或起重機(jī)架設(shè)到適當(dāng)位置。拱橋是在腳手架或臨時(shí)腳手架上施工的，這種方法通常用于預(yù)應(yīng)力混凝土拱橋。然而對(duì)鋼拱橋來說已發(fā)展了一種技術(shù)，用這種技術(shù)將已裝好的部分借助起支承作用的鋼索控制就位（鋼拱在安裝過程中還沒有合攏前，是兩個(gè)懸臂，需要用鋼索拉住兩個(gè)懸臂以免傾倒）。當(dāng)鋼索中的拉力增加時(shí)，起重機(jī)就沿著拱橋的頂部移動(dòng)以架設(shè)新的鋼拱。對(duì)懸索橋來說，需要首先施工基礎(chǔ)和索塔。這時(shí)鋼索從錨碇（一個(gè)固定鋼索的大混凝土塊）穿過直至索塔并且通過另一索塔而錨固在錨碇上，然后從卷線盤上放松鋼索的輪子沿著鋼索運(yùn)動(dòng)，當(dāng)卷線盤到達(dá)另一面時(shí)，另一根鋼絲又裝進(jìn)卷線盤并最終到達(dá)它的原位置。當(dāng)所有的鋼索被放在固定的位置后，另一臺(tái)機(jī)器沿著鋼索移動(dòng)并對(duì)其進(jìn)行張拉錨固。當(dāng)鋼索施工完畢時(shí)，逐漸開始在支架上從兩端向中間施工。在橋梁下部結(jié)構(gòu)和基礎(chǔ)設(shè)計(jì)中要考慮的荷載包括：從上部結(jié)構(gòu)傳下來的荷載和直接作用于下部結(jié)構(gòu)的基礎(chǔ)的荷載。AASHTO荷載。AASHTO規(guī)范第三部分總結(jié)了橋梁設(shè)計(jì)（上、下部結(jié)構(gòu)）要考慮的荷載和作用力。主要有：恒載、活載、活載沖擊力或動(dòng)力作用、風(fēng)荷載以及其他荷載——如縱向力、離心力、溫度力、土壓力、浮力、收縮及徐變、拱肋縮短、安裝應(yīng)力、冰及水流壓力、沖撞力及地震應(yīng)力。除了這些通常能夠量化大的典型荷載外， AASHTO同樣認(rèn)識(shí)到諸如活動(dòng)支座處產(chǎn)生的摩擦以及由于橋梁的沉降差而產(chǎn)生的應(yīng)力等間接荷載效應(yīng)。LRFD規(guī)范將荷載按不同的方式劃分為兩種：永久作用和可變作用。永久作用荷載：包括所有橋梁構(gòu)件、器件及輔助設(shè)備、道路面層的凈重及未來鋪裝重量、填土恒載。AASHTO及LRFD規(guī)范都給出了表格，總結(jié)了橋梁工程重常用的單位重量。可變作用汽車荷載 小跨度橋梁的汽車荷載：美國(guó)和加拿大已致力于發(fā)展一種比 HAASHTO模型更實(shí)際的代表高速公路活荷載的模型。到目前為止， AASHTO

或HS模型仍被廣泛采用。BridgeConstructionTechniquesThefinalcostofabridgeisthesumofthecostofpermanentmaterials,theproportionatecosttotheprojectofplantandtemporaryworksandthecostoflabor.Thecostofpermanentmaterialscanbeestimatedreasonablycorrectly.Withexperience,abridgecontractorcandealcompletelywithcostofplantandtemporaryworks.Butthelaborcostdoesnotlenditselftoexactanalysis.Recentcompetitivedesignshaveattemptedtointroduceinnovationsinconstructionmethodswithaviewtoeffecteconomyinthecostonlaborbyreducingtemporaryworksandbyminimizingthedurationofsitework.Thesuitabletechniquesofconstructionofbridgesuperstructurewillvaryfromsitetosite,andwilldependonthespansandlengthofthebridge,typeofthebridge,materialsusedandsiteconditions.Forinstance,cast-in-siteconcreteconstructioncouldbeadoptedforshortspansupto40m,iftheriverbedisdryforaconsiderateportionoftheyear,whereasfreecantileverconstructionwithprestressedconcretedeckingwouldbeappropriateforlongspansinriverswithnavigationalrequirements.Thecurrenttrendistowardstheavoidanceofstagingasmuchaspossibleandtouseprecastorprefabricatedcomponentstomaximumextent.Also,constructionmachinerysuchascranesandlaunchinggirdersarecomingintowideruse.Thesearegreatersavingstobeeffectedbypayingattentiontothemethodofconstructionevenfromthedesignstagethanbyattackingpermanentmaterials.ShortSpanBridgesForbridgesinvolvingspansupto40m,thesuperstructuremaybebuiltonstagingsupportedontheground.Alternatively,thegirdersmaybeprecastforthefullspanlengthanderectedusinglaunchinggirdersorcranes,ifthebridgehasmanyequalspans.Inthelatterprocedure,theadditionalcostonerectionequipmentshouldbelessthanthesavinginthecostofformworkandinthelabourcostresultingfromfasterconstruction.LongSpanConcreteBridgesLongspanconcretebridgesareusuallyofpost-tensionedconcreteandconstructedeitherasconditionsbeamstypesorasfreevercantilestructures.Manymethodshavebeendevelopedforcontinuousdeckconstruction.Iftheclearancebetweenthegroundandbottomofthedeckissmallandthesoilisfirm,thesuperstructurecanbebuiltonstaging.Thismethodisbecomingobsolete.Currently,free-cantileverandmovablescaffoldsystemsareincreasinglyusedtosavetimeandimprovesafety.Themovablescaffoldsystememploysmovableformsstiffenedbysteelframes.Theseformsextendonespanlengthandaresupportedbysteelgirderswhichrestonapieratoneendandcanbemovedfromspantospanonasecondsetofauxiliarysteelgirders.Aneconomicalconstructiontechniqueknownasincrementalpush-launchingmethoddevelopedbyBaur-LeonhardteamisshownschematicallyinFigure22.1.Thetotalcontinuousdeckissubdividedlongitudinallyintosegmentsof10to30mlengthdependingonthelengthofspansandthetimeavailableforconstruction.Eachofthesesegmentsisconstructedimmediatelybehindtheabutmentofthebridgeinsteelframedforms,whichremaininthesameplaceforconcretingallsegments.Theformsaresodesignedastobecapableofbeingmovedtransverselyorrotatedonhingestofacilitateeasystrippingaftersufficienthardeningofconcrete.Attheheadofthefirstsegment,asteelnoseconsistingofalighttrussisattachedtofacilitatereachingofthefirstandsubsequentpierswithoutincludingatoolargecanyilevermomentduringconstruction.Thesecondandthefollowingsegmentsareconcreteddirectlyonthefaceofthehardenedportionandthelongitudinalreinforcementcancontinueacrosstheconstructionjoint.Thepushingisachievedbyhydraulicjackswhichactagainsttheabutment.SincethecoefficientoffrictionofTeflonslidingbearingsisonlyabout2percent,lowcapacityhydraulicjackswouldsufficetomovethebridgeevenoverlonglengthsofseveralhundredmetres.Thismethodcanbeusedforstraightandcontinuouslycurvedbridgesuptoaspanofabout120m.Thefree-cantileversystemwaspioneeredbyDyckerhoffandWillmanningermany.Inthissystem,thesuperstructureiserectedbymeansofcantilevertruckinsectionsgenerallyof3.5m.Thecantilevertruck,whosecostisrelativelysmallandwhichisattachedfirmlytopermanentconstruction,ermitsbyrepeatedusetheconstructionoflargebridges.Theavoidanceofscaffoldfrombelow,thespeedofworkandthesavinginlabourcostresultintheconstructionbeingveryeconomicdal.Thefree-cantileversystemisideallysuitedforlaunchedgirderswithalargedepthabovethepiercantileversystemisideallysuitedforlaunchedgirderswithalargedepthabovethepiercantileveringtothemiddleofthespan.Anothertechniqueistheuseofthepneumaticcaisson.Thecaissonisahugecylinderwithabottomedgethatcancutintothewaterbed.Whencompressedarispumpedintoit,thewaterisforcedout.Caissonsmustbeusedwithextremecare.foronething,workerscanonlystayinthecompressionchamberforshortperiodsoftime.Foranother,iftheycomeuptonormalatmosphericpressuretoorapidly,theyaresubjecttothebends,orcaissondiseaseasitisalsocalled,whichisacripplingorevenfatalconditioncausedbyexcessnitrogenintheblood.WhentheEadsBridgeacrosstheMississippiRiveratSt.Louiswasunderconstructionbetween1867and1874,atatimewhenthedangerofworkingincompresedairwasnotfullyunderstood,fourteendeathswascausedbythebends.Whenextrastrengthisnecessaryinthepiers,theysometimeskeyedintothebedrock-thatis,theyareextendeddownintothebedrock.ThismethodwasusedtobuildthepiersfortheGoldenGateBridgeinSanFrancisco,whichissubjecttostrongtidiesandhighwinds,andislocatedinanearthquakezone.Thedrillingwascarriedoutunderwaterbydeep-seadivers.Wherebedrockcannotbereached,pilesaredrivenintothewaterbed.Today,thepilesinconstructionareusuallymadeofprestressedconcretebeams.Oneingenioustechnique,usedfortheTappanZeeBridgeacrosstheHudsonRiverinNewYork,istorestahollowconcreteboxontopofalayerofpiles.Whentheboxispumpeddry,itbecomesbuoyantenoughtosupportalargeproportionoftheweightofthebridge(seeFig.22.3).Eachtypeofbridge,indeedeachindividualbridge,presentsspecialconstructionproblems.Withsometrussbridges,thespanisfloatedintopositionafterthepiershavebeenerectedandthenraisedintoplacebymeansofjacksorcranes.Archbridgescanbeconstructedoverafalsework,ortemporaryscaffolding.Thismethodisusuallyemployedwithreinforcedconcretearchbridges.Withsteelarches,however,atechniquehasbeendevelopedwherebythefinishedsectionsareheldinplacebywiresthatsupplyacantileversupport.Cranesmovealongthetopofthearchtoplacenewsectionsofsteelwhilethetensioninthecablesincreases.Withsuspensionbridges,thefoundionsandthetowersarebuiltfirst.Thenacableisrunfromtheanchorage-aconcreteblockinwhichthecableisfastened-uptothetowerandacrosstotheoppositetowerandanchorage.Awheelthatunwindswirefromareelqunsalongthiscable.Whenthereelreachestheotherside,anotherwireisplacedonit,andthewheelreturnstoitsoriginalposition.Whenallthewireshavebeenputinplace,anothermachinemovesalongthecabletocampactandtobindthem.Constructionbeginsonthedeckwhenthecablesareinplace,withworkprogressingtowardthemiddlefromeachendofthestructure.Theloadstobeconsideredinthedesignofsubstructuresandbridgefoundationsincludeloadsandforcestransmittedfromthesuperstructure,andthoseactingdirectlyonthesubstructureandfoundation.AASHTOloads.Section3ofAASHTOspecificationssummarizestheloadsandforcestobeconsideredinthedesignofbridges(superstructureandsubstructure).Briefly,thesearedeadload,liveload,iMPactordynamiceffectofliveload,