土木工程專(zhuān)業(yè)英語(yǔ)lesson-19-arch-bridge拱橋

TherelevanttermsthatareusedtodescribethevariouspartsofanarchbridgeareshowninFigure1.在圖1中顯示用來(lái)描述一個(gè)拱橋的各部分的有關(guān)術(shù)語(yǔ)。Archesmaybegroupedaccordingtothefollowingparameters:拱橋可以根據(jù)以下參數(shù)進(jìn)行分組：1.thematerialsofconstruction2.thestructuralarticulation3.theshapeofthearch1．建筑材料2．結(jié)構(gòu)的銜接 3．拱橋的形狀Historically,archbridgesareassociatedwithstonemasonry.Thisgavewaytobrickworkinthenineteenthcentury.Becausethesewereproportionedtominimisethepossibilityoftensilestress,theytendtobefairlymassivestructures.從歷史上看，拱橋都是與石頭建筑有聯(lián)系的，但是在十九世紀(jì)讓位給了磚砌結(jié)構(gòu)。因?yàn)樗麄兊谋壤M可能的減少了拉伸應(yīng)力的可能性，這使得他們有成為巨大結(jié)構(gòu)的趨勢(shì)。 Bycomparisontheuseofreinforcedconcreteandmodernstructuralsteelgivestheopportunityforslender,elegantarches.相比之下，使用鋼筋混凝土和現(xiàn)代結(jié)構(gòu)鋼為拱橋提供了簡(jiǎn)約、典雅的機(jī)會(huì)。Withregardtostructuralarticulationthearchcanbefixedorhinged.Inthelattercaseeitherone,twoorthreehingescanbeincorporatedintothearchrib.Whilstthefixedarchhasthreeredundancies,theintroductionofeachhingereducedtheindeterminacybyoneuntil,withthreehinges,thearchisstaticallydeterminateandhence,theoretically,freeoftheproblemsofsecondarystresses.Figure2showsarangeofpossiblearrangements.Thearticulationofthearchisnotonlydependentuponthenumberofhingesbutisalsofundamentallyinfluencedbythepositionofthedeckandthenatureoftheloadtransferfromthedecktothearch.至于銜接拱結(jié)構(gòu)可固接或鉸接。在后一種情況中一個(gè)、兩個(gè)或三個(gè)鉸鏈可以被使用到拱肋。雖然固結(jié)的拱橋存在三個(gè)多余約束，但是一個(gè)鉸的作用就是減少一個(gè)多余約束，而對(duì)于三個(gè)鉸來(lái)說(shuō)的拱橋是靜定的，因此，從理論上來(lái)講，無(wú)二次應(yīng)力問(wèn)題。圖2顯示了一系列可能的布置情況。拱橋的銜接不僅僅取決于鉸的數(shù)量，也從根本上受到橋面的位置和從橋面?zhèn)飨蚬暗暮奢d性質(zhì)的影響。Thetraditionalfilledspandrel,wherethevehicularloadingistransferredthroughthebackfillmaterialontotheextradosofthearch,representsatfirstglancethesimpleststructuralcondition.Aswillbeseenlaterthisisnotthecaseandhasledtomuchresearchforthespecificcaseofthemasonryarchbridgeinanattempttoimproveourunderstandingofsuchstructures.傳統(tǒng)的填充拱肩是車(chē)輛荷載通過(guò)其回填材料傳遞到拱背，這是第一眼能夠看到的最簡(jiǎn)單的結(jié)構(gòu)狀況。但是稍后我們看到的就不是這種狀況，這就導(dǎo)致了我們?cè)谠噲D提高對(duì)這種結(jié)構(gòu)的認(rèn)識(shí)時(shí)，將要對(duì)這種磚石拱橋的許多特定案例進(jìn)行研究。Thespandrelmaybeopenwithcolumnsand/orhingesusedtotransferthedeckloadstothearch.Inanattempttominimisethehorizontalthrustontheabutments,thedeckmaybeusedto‘tie’thearch.Tiedarchesareparticularlyappropriatewhendeckconstructiondepthsarelimitedandlargeclearspansareneeded(particularlyifgroundconditionsarealsodifficultandwouldrequireextensivepilingtoresistthehorizontalthrusts).帶有柱子的拱肩會(huì)被做成開(kāi)放式的，鉸用來(lái)傳遞橋面板的荷載到拱。在試圖盡量減少對(duì)橋墩的水平推力時(shí)，橋面板就會(huì)和系桿拱配合使用。當(dāng)橋面的建設(shè)深度受到限制時(shí)或者需要大跨度時(shí)（特別是如果地面條件也很困難，將需要大量的樁以抵抗水平推力時(shí)），系桿拱就會(huì)特別的適用。Foreaseofsettingoutandconstructionsimplershapesareadoptednowadayssegmentalorparabolicshapesareused.Althoughinsituationswheremaximumwidthsofheadroomhavetobeprovided(sayoverarailway,roadorcanal)anellipticalshapemayberequiredoritsnearest‘easy’equivalentthethree-centredarch.為了便于施工放樣，簡(jiǎn)單的建筑物形狀現(xiàn)在被分段采用或者采用拋物線形狀。雖然在最大寬度的情況下凈空必須提供（比如在一個(gè)鐵路，公路或運(yùn)河），橢圓形狀可能是其最接近的要求或其最相近的等價(jià)物是“簡(jiǎn)單”的三個(gè)鉸的拱。Itisworthcommentingatthisstageregardingtheidealizationofarchstructures.Traditionallyarchesareperceivedasbeingtwo-dimensionalstructures;this,ofcourseisnottrue–buttheextenttowhichitisnottrueshouldbeofconcerntothedesigner/assessor.Eveninthecaseofathree-hingedarchwhichostensiblyisstaticallydeterminatethe‘pins’arecapableoftransmittingsheareventhoughtheytheoreticallycannottransmitmoments.Inthecaseofnon-uniformtransversedistributionofloadingthehingeswilltransmitavaryingshearwhichwillproducetorsioninthearch.Moreover,inthecaseofskewarchesornon-verticalribsthestructurehasamuchhigherredundancyandhencewillrequiregreaterattentiontodetailinregardtothereleaseswhichareengineeredintothestructure.這是值得在現(xiàn)階段討論的理想化的拱結(jié)構(gòu)。傳統(tǒng)意義上，拱被認(rèn)為是二維結(jié)構(gòu)。這當(dāng)然是不真實(shí)的——但它在何種程度上是不正確的應(yīng)該是設(shè)計(jì)師和評(píng)估員所關(guān)心的問(wèn)題。即使在表面上看是靜定的三鉸拱的情況下，“插腳”都能傳遞剪力，即使他們理論上不能傳遞。非均勻的荷載橫向分布的情況下，鉸鏈會(huì)傳遞一個(gè)會(huì)在拱內(nèi)產(chǎn)生扭矩的不斷變化的剪力。此外，斜拱或非垂直拱肋的情況下，結(jié)構(gòu)具有很高的冗余，因此將需要更多地注意發(fā)布的工程結(jié)構(gòu)方面的詳細(xì)信息。Fromanaestheticpointofview,archeshaveauniversalappeal.Inspiteofthis,caremustbetakenastheimpactofevenmodestsizedbridgesissignificant.Filledarchesareinvariablymasonry(orwideningofmasonry)bridges.Cleannessofline,honestyofconceptionandtheattentiontodetailarevitalingredientstoasuccessfulbridge.Certainly,simplestringcoursesandcopingsarepreferabletoelaboratedetailswhichwouldbeexpensiveandinappropriateformostmodernbridges.Wherestoneisuseditisimportanttobesensitivetothenatureofthematerial.Modernquarryingtechniquesshouldbeemployed(lasercutting,diamondsawing,flametexturingandsandblasting)reservingtraditionaldressingtoconservationschemes.Ifbrickworkisuseddifferenttexturedorcolouredbricksandmortarcanbespecified.Herestringcoursescanbeparticularlyusefultomaskchangesinbeddingangle.從美學(xué)的角度來(lái)看，拱橋有一個(gè)普遍的吸引力。盡管這樣，重視規(guī)模不大的橋梁的影響是十分有意義的。實(shí)體的拱橋總是磚石（或磚石擴(kuò)大）橋梁。行清潔、誠(chéng)信的理念和注重細(xì)節(jié)是成功的橋梁的至關(guān)重要的因素。當(dāng)然，簡(jiǎn)單的層拱和頂層更適合詳細(xì)描述一些昂貴的和與許多現(xiàn)代橋梁不相稱的細(xì)節(jié)。使用石頭是因?yàn)樗馁|(zhì)重要的環(huán)境敏感性。應(yīng)采用現(xiàn)代開(kāi)采技術(shù)（激光切割、金剛石鋸、火焰變形和噴砂)，保留傳統(tǒng)加工保護(hù)計(jì)劃。如果使用不同的磚砌體可以指定紋理或琉璃磚和灰泥。在這里，層拱可以很有效的掩飾層面方向上的變化。Historicallyabutmentscomprisedeitherrock,orelseweremassivemasonrysupportsrelyingontheirweighttoresistthethrustofthearch.Intermsofstructuralhonestythisisnecessaryasitisinstinctivetoexpectsuchsupport.從歷史上看，橋墩是由巖石或者是大量的厚重磚石結(jié)構(gòu)組成的，依靠自身的重量抵抗拱橋的推力。依靠結(jié)構(gòu)的穩(wěn)定性，這是必要的，因?yàn)檫@是一種本能去期待這種支持。Reinforcedconcreteandsteelarchesarealtogethermuchlighterstructures.‘Thestructureconsistsbasicallyofthearch,thedeckandusuallysomesupportsfromthearchtothedeck–inthatorderofimportance.Theseelementsshouldbeexpressedinbothformanddetail,andwithdueregardfortheirhierarchy’(HighwaysAgency,1996).鋼筋混凝土橋和鋼拱橋有許多輕結(jié)構(gòu)。結(jié)構(gòu)基本上包括拱、橋面板和通常一些拱肋到橋面板的支撐結(jié)構(gòu)——重要的順序。這些元素應(yīng)該表現(xiàn)在細(xì)節(jié)和形式上，并充分考慮其層次性Itisimportantthatthedeck,ifitrestsonthecrownofthearch,shouldnotmaskitinanyway.Anysupportwhetherspandrelcolumnsorhinges(inthecaseofthetiedarch)shouldnotbeallowedtodominate.Preferablytheyshouldberecessedrelativetotheparapetandstringcourse.重要的是，如果在拱頂處的橋面板，不應(yīng)該用任何方法去掩飾它。無(wú)論是層拱還是鉸鏈的任何支撐結(jié)構(gòu)（在系桿拱橋的情況下