土木工程專業(yè)英語lesson 19 arch bridge拱橋

1、TherelevanttermsthatareusedtodescribethevariouspartsofanarchbridgeareshowninFigure1.在圖1中顯示用來描述一個拱橋的各部分的有關(guān)術(shù)語。Archesmaybegroupedaccordingtothefollowingparameters:拱橋可以根據(jù)以下參數(shù)進(jìn)行分組：thematerialsofconstructionthestructuralarticulationtheshapeofthearch1建筑材料2結(jié)構(gòu)的銜接Historically,archbridgesareassociatedwithstone

2、masonry.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)。因為他們的比例盡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。Bycomparisontheuseofreinforcedconcreteandmodernstructuralsteelgivest

3、heopportunityforslender,elegantarches.相比之下，使用鋼筋混凝土和現(xiàn)代結(jié)構(gòu)鋼為拱橋提供了簡約、典雅的機(jī)會Withregardtostructuralarticulationthearchcanbefixedorhinged.Inthelattercaseeitherone,twoorthreehingescanbeincorporatedintothearchrib.Whilstthefixedarchhasthreeredundancies,theintroductionofeachhingereducedtheindeterminacybyoneunti

4、l,withthreehinges,thearchisstaticallydeterminateandhence,theoretically,freeoftheproblemsofsecondarystresses.Figure2showsarangeofpossiblearrangements.Thearticulationofthearchisnotonlydependentuponthenumberofhingesbutisalsofundamentallyinfluencedbythepositionofthedeckandthenatureoftheloadtransferfromt

5、hedecktothearch.至于銜接拱結(jié)構(gòu)可固接或鉸接。在后一種情況中一個、兩個或三個鉸鏈可以被使用到拱肋。雖然固結(jié)的拱橋存在三個多余約束，但是一個鉸的作用就是減少一個多余約束，而對于三個鉸來說的拱橋是靜定的，因此，從理論上來講，無二次應(yīng)力問題。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,wherethevehicularloadingistransferredthroughthebackfillmaterialontotheextradosofthearc

6、h,representsatfirstglancethesimpleststructuralcondition.Aswillbeseenlaterthisisnotthecaseandhasledtomuchresearchforthespecificcaseofthemasonryarchbridgeinanattempttoimproveourunderstandingofsuchstructures.傳統(tǒng)的填充拱肩是車輛荷載通過其回填材料傳遞到拱背，這是第一眼能夠看到的最簡單的結(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)致了我們在試圖提高對這種結(jié)構(gòu)的認(rèn)識時，將要對這種磚石拱橋的許多

7、特定案例進(jìn)行研究。Thespandrelmaybeopenwithcolumnsand/orhingesusedtotransferthedeckloadstothearch.Inanattempttominimisethehorizontalthrustontheabutments,thedeckmaybeusedtotiethearch.Tiedarchesareparticularlyappropriatewhendconstructiondepthsarelimitedandlargeclearspansareneeded(particularlyifgroundconditionsa

8、realsodifficultandwouldrequireextensivepilingtoresistthehorizontalthrusts).帶有柱子的拱肩會被做成開放式的，鉸用來傳遞橋面板的荷載到拱。在試圖盡量減少對橋墩的水平推力時，橋面板就會和系桿拱配合使用。當(dāng)橋面的建設(shè)深度受到限制時或者需要大跨度時(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)，系桿拱就會特別的適用。Foreaseofsettingoutandconstructionsimplershapesareadoptednowadayssegmentalorparabolicshapesareused.A

9、lthoughinsituationswheremaximumwidthsofheadroomhavetobeprovided(sayoverarailway,roadorcanal)anellipticalshapemayberequiredoritsnearesteasyequivalentthethree-centredarch.為了便于施工放樣，簡單的建筑物形狀現(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(比如在一個鐵路，公路或運河)，橢圓形狀可能是其最接近的要求或其最相近的等價物是“簡單”的三個鉸的拱。刖(1)s-ften&dcmerapm生I(d)T啣oWng

10、ed血惻Three+ihgedflbb|Mlngeiessrtbf)FligErajna(Iwo-呵関;譏iSowspaMrel(ijnMaranpcttglrtigrrurg&rglidHl-、訶Gne-nlngedrib型Open單arwi常i；bjBfsekIspandrynainM!剳raiz阿ar弗眥因Ehi；p)CcnvenlirnaJa!chwnhmoniEnl-resfelanlrib|q；snffenacdKJan料HngelessribCOtllTTlSTig刃an出I的UMardn(miirefiMdI嗎rranfiRgure2咖桓ofarchMtige*tffTl)It

11、isworthcommentingatthisstageregardingtheidealizationofarchstructures.Traditionallyarchesareperceivedasbeingtwo-dimensionalstructures;this,ofcourseisnottruebuttheextenttowhichitisnottrueshouldbeofconcerntothedesigner/assessor.Eveninthecaseofathree-hingedarchwhichostensiblyisstaticallydeterminatethepi

12、nsarecapableoftransmittingsheareventhoughtheytheoreticallycannottransmitmoments.Inthecaseofnon-uniformtransversedistributionofloadingthehingeswilltransmitavaryingshearwhichwillproducetorsioninthearch.Moreover,inthecaseofskewarchesornon-verticalribsthestructurehasamuchhigherredundancyandhencewillrequ

13、iregreaterattentiontodetailinregardtothereleaseswhichareengineeredintothestructure.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)然是不真實的但它在何種程度上是不正確的應(yīng)該是設(shè)計師和評估員所關(guān)心的問題。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，鉸鏈會傳遞一個會在拱內(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。Fromanaesthe

14、ticpointofview,archeshaveauniversalappeal.Inspiteofthis,caremustbetakenastheimpactofevenmodestsizedbridgesissignificant.Filledarchesareinvariablymasonry(orwideningofmasonry)bridges.Cleannessofline,honestyofconceptionandtheattentiontodetailarevitalingredientstoasuccessfulbridge.Certainly,simplestring

15、coursesandcopingsarepreferabletoelaboratedetailswhichwouldbeexpensiveandinappropriateformostmodernbridges.Wherestoneisuseditisimportanttobesensitivetothenatureofthematerial.Modernquarryingtechniquesshouldbeemployed(lasercutting,diamondsawing,flametexturingandsandblasting)reservingtraditionaldressing

16、toconservationschemes.Ifbrickworkisuseddifferenttexturedorcolouredbricksandmortarcanbespecified.Herestringcoursescanbeparticularlyusefultomaskchangesinbeddingangle.從美學(xué)的角度來看，拱橋有一個普遍的吸引力。盡管這樣，重視規(guī)模不大的橋梁的影響是十分有意義的。實體的拱橋總是磚石(或磚石擴(kuò)大)橋梁。行清潔、誠信的理念和注重細(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

17、是因為它材質(zhì)重要的環(huán)境敏感性。應(yīng)采用現(xiàn)代開采技術(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.IntermsofstructuralTTThonestythisisnecessaryasitisinstinctivetoexpectsuchsuppo

18、rt.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，因為這是一種本能去期待這種支持。Reinforcedconcreteandsteelarchesarealtogethermuchlighterstructures.Thestructureconsistsbasicallyofthearch,thedeckandusuallysomesupportsfromthearchtothedeckinthatorderofimportance.Theseelementsshouldbeexpressedinbothformandd

19、etail,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