外文翻譯---橋梁施工方法

1、<p><b>　　外文翻譯</b></p><p>　　Bridge Construction Techniques</p><p>　　The final cost of a bridge is the sum of the cost of permanent materials,the proportionate cost to the projec

2、t of plant and temporary works and the cost of labor .The cost of permanent materials can be estimated reasonably correctly.With experience,a bridge contractor can deal completely with cost of plant and temporary works .

3、But the labor cost does not lend itself to exact analysis .Recent competitive designs have attempted to introduce innovations in construction methods with a view to effec</p><p>　　The suitable techniques of

4、construction of bridge superstructure will vary from site to site,and will depend on the spans and length of the bridge, type of the bridge,materials used and site conditions. For instance, cast-in-site concrete construc

5、tion could be adopted for short spans up to 40 m, if the river bed is dry for a considerate portion of the year, whereas free cantilever construction with prestressed concrete decking would be appropriate for long spans

6、in rivers with navigational requi</p><p>　　Short Span Bridges</p><p>　　For bridges involving spans up to 40 m , the superstructure may be built on staging supported on the ground . Alternatively

7、 , the girders may be precast for the full span length and erected using launching girders or cranes,if the bridge has many equal spans.In the latter procedure , the additional cost on erection equipment should be less t

8、han the saving in the cost of formwork and in the labour cost resulting from faster construction .</p><p>　　Long Span Concrete Bridges</p><p>　　Long span concrete bridges are usually of post-te

9、nsioned concrete and constructed either as conditions beams types or as free ver cantile structures . Many methods have been developed for continuous deck construction . If the clearance between the ground and bottom of

10、the deck is small and the soil is firm , the superstructure can be built on staging . This method is becoming obsolete . Currently , free-cantilever and movable scaffold systems are increasingly used to save time and imp

11、rove safety</p><p>　　The movable scaffold system employs movable forms stiffened by steel frames . These forms extend one span length and are supported by steel girders which rest on a pier at one end and ca

12、n be moved from span to span on a second set of auxiliary steel girders .</p><p>　　An economical construction technique known as incremental push-launching method developed by Baur-Leonhard team is shown sch

13、ematically in Figure 22.1. </p><p>　　The total continuous deck is subdivided longitudinally into segments of 10 to 30 m length depending on the length of spans and the time available for construction . Each

14、of these segments is constructed immediately behind the abutment of the bridge in steel framed forms , which remain in the same place for concreting all segments .The forms are so designed as to be capable of being moved

15、 transversely or rotated on hinges to facilitate easy stripping after sufficient hardening of concrete. At the</p><p>　　The free-cantilever system was pioneered by Dyckerhoff and Willmann in germany .In this

16、 system , the superstructure is erected by means of cantilever truck in sections generally of 3.5 m .The cantilever truck ,whose cost is relatively small and which is attached firmly to permanent construction , ermits by

17、 repeated use the construction of large bridges . The avoidance of scaffold from below ,the speed of work and the saving in labour cost result in the construction being very economicdal . The f</p><p>　　Anot

18、her technique is the use of the pneumatic caisson .The caisson is a huge cylinder with a bottom edge that can cut into the water bed . When compressed ar is pumped into it ,the water is forced out .Caissons must be used

19、with extreme care .for one thing, workers can only stay in the compression chamber for short periods of time .For another , if they come up to normal atmospheric pressure too rapidly ,they are subject to the bends ,or ca

20、isson disease as it is also called , which is a cripplin</p><p>　　When extra strength is necessary in the piers ,they sometimes keyed into the bedrock-that is ,they are extended down into the bedrock .This m

21、ethod was used to build the piers for the Golden Gate Bridge in San Francisco ,which is subject to strong tidies and high winds ,and is located in an earthquake zone .The drilling was carried out under water by deep-sea

22、divers .</p><p>　　Where bedrock cannot be reached ,piles are driven into the water bed .Today ,the piles in construction are usually made of prestressed concrete beams .One ingenious technique ,used for the

23、Tappan Zee Bridge across the Hudson River in New York ,is to rest a hollow concrete box on top of a layer of piles .When the box is pumped dry ,it becomes buoyantenough to support a large proportion of the weight of the

24、bridge (see Fig.22.3). </p><p>　　Each type of bridge ,indeed each individual bridge ,presents special construction problems.With some truss bridges ,the span is floated into position after the piers have bee

25、n erected and then raised into place by means of jacks or cranes .Arch bridges can be constructed over a falsework ,or temporaryscaffolding.This method is usually employed with reinforced concrete arch bridges .With stee

26、l arches ,however ,a technique has been developed whereby the finished sections are held in place by wires</p><p>　　With suspension bridges ,the foundions and the towers are built first .Then a cable is run

27、from the anchorage-aconcrete block in which the cable is fastened-up to the tower and across to the opposite tower and anchorage .Awheel that unwinds wire from a reel quns along this cable .When the reel reaches the othe

28、r side ,another wire is placed on it ,and the wheel returns to its original position .When all the wires have been put in place ,another machine moves along the cable to campact and to bind</p><p>　　The load

29、s to be considered in the design of substructures and bridge foundations include loads and forces transmitted from the superstructure, and those acting directly on the substructure and foundation .</p><p>　　

30、AASHTO loads . Section 3 of AASHTO specifications summarizes the loads and forces to be considered in the design of bridges (superstructure and substructure ) . Briefly , these are dead load ,live load , iMPact or dynami

31、c effect of live load , wind load , and other forces such as longitudinal forces , centrifugal force ,thermal forces , earth pressure , buoyancy , shrinkage and long term creep , rib shortening , erection stresses , ice

32、and current pressure , collision force , and earthquake stre</p><p>　　Permanent loads </p><p>　　Dead Load : this includes the weight DC of all bridge components , appurtenances and utilities, we

33、aring surface DW and future overlays , and earth fill EV. Both AASHTO and LRFD specifications give tables summarizing the unit weights of materials commonly used in bridge work .</p><p>　　Transient Loads <

34、;/p><p>　　Vehicular Live Load (LL) </p><p>　　Vehicle loading for short-span bridges :considerable effort has been made in the United States and Canada to develop a live load model that can represen

35、t the highway loading more realistically than the H or the HS AASHTO models . The current AASHTO model is still the applicable loading.</p><p><b>　　橋梁施工方法</b></p><p>　　一座橋梁的最終造價是建造橋梁

36、結(jié)構(gòu)物的材料費用與這項工程相關(guān)的機械費用和臨時工程及勞動力的費用的總和。材料的費用能夠被預(yù)算的相當準確的，承包商們借助施工經(jīng)驗是能夠估算施工機械和勞動力的費用的。但是勞動力的費用是不能夠精確分析的。最近的一項比較有競爭力的設(shè)計試圖通過減少臨時工程和工程的工期來革新施工方法。</p><p>　　橋梁上部結(jié)構(gòu)比較適宜的施工方法將隨施工場地不同而不同，并主要取決于橋梁的長度和跨度、橋梁的類型、基礎(chǔ)條件及其所使用的材料

37、。例如：現(xiàn)場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?，F(xiàn)在的發(fā)展趨勢是盡可能避免使用臺架施工，而在最大程度上采用預(yù)制構(gòu)件；另一方面，起重機、滑拽梁等施工機械的應(yīng)用范圍也越來越廣。這些都是從對施工方法的密切關(guān)注甚至是設(shè)計過程的密切關(guān)注而取得的巨大收獲，而不是在善于解決永久材料。</p><p><b

38、>　　小跨度橋梁</b></p><p>　　當橋梁的跨度小于40米左右時，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)備而增加的費用和由于施工工期短而減少的費用之和將會比前一種施工方法的模板制作費用低。</p><p><b>　　大跨度橋梁<

39、;/b></p><p>　　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)越來越過時了。目前，自由懸臂法和移動模架法的應(yīng)用漸廣并能節(jié)省時間和提高安全性。</p><p>　　移動模架法是利用固定在鋼制臺架上的移動系統(tǒng)而形成，這種

40、系統(tǒng)能夠達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梁逐跨移動的鋼梁上。</p><p>　　一種經(jīng)濟的施工方法是被廣泛知曉的由Baur-leonhard團隊所發(fā)展的使用廣泛的頂推法。整個的連續(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間。每個節(jié)段在橋臺后面的鋼模上能夠快速澆注，鋼模可以周轉(zhuǎn)使用而澆注所有的節(jié)段。這樣設(shè)計模板是為了能夠橫向移動或在鉸上轉(zhuǎn)動，以便在混凝土充分硬化

41、后脫模。在第一節(jié)段的頂端安裝上一個由輕型桁架組成的鋼導梁，以實現(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上的液壓千斤頂實現(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度甚至達數(shù)百米的橋梁的頂推。這種方法可以應(yīng)用在長度在120米左右的直線橋梁或曲線橋梁上。</p><p&

42、gt;　　自由懸臂法是由法國的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)段長度基本在3.5米的懸臂機上施工，懸臂機的費用相對比較低并且固定在橋梁承重結(jié)構(gòu)上，由于它的重復(fù)利用性使它能在長橋上使用。由于施工速度的加快和時間的節(jié)省使得這種施工方法的費用比較低從而避免了使用臺架施工，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。</p><p>　　另一種施工方法是

43、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。當壓縮空氣進入沉箱內(nèi)部時水就會被排出。沉箱的利用必須嚴加注意。首先，工人們只能在這種壓縮空氣的空間里呆很短的時間；另一方面，如果工人們從沉箱進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?。?，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。</p><p>　　當St.louis市的密西西比河Eads上的橋在

44、1867-1874年施工時，由于人們對在壓縮空氣中工作的危險性認識不足，最后由于患潛水病而導致14人死亡。</p><p>　　當在橋墩上有外力作用時，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)用來建造位于強風和地震區(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行的。</p><p>　　在不能到達基巖的地方，樁通常被打進河床。今天，在施工的基樁基本上是預(yù)

45、應(yīng)力混凝土結(jié)構(gòu)。在建造紐約哈德遜河上的泰平.吉橋時所采用的一種巧妙技術(shù)是將一個空心混凝土箱置于橋樁層上，當它里面的水被抽干時，它的浮力足夠支承橋梁重力的一大部分。</p><p>　　每一種類型的橋梁實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到已施工完畢的基樁位置，然后再利用千斤頂或起重機架設(shè)到適當位置。拱橋是在腳手架或臨時腳手架上施工的，這種方法通常用于預(yù)應(yīng)力混凝土拱橋。然而對鋼拱橋來說已發(fā)展了一

46、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，是兩個懸臂，需要用鋼索拉住兩個懸臂以免傾倒）。當鋼索中的拉力增加時，起重機就沿著拱橋的頂部移動以架設(shè)新的鋼拱。</p><p>　　對懸索橋來說，需要首先施工基礎(chǔ)和索塔。這時鋼索從錨碇（一個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動，當卷線盤到達另一面時，另一

47、根鋼絲又裝進卷線盤并最終到達它的原位置。當所有的鋼索被放在固定的位置后，另一臺機器沿著鋼索移動并對其進行張拉錨固。當鋼索施工完畢時，逐漸開始在支架上從兩端向中間施工。</p><p>　　在橋梁下部結(jié)構(gòu)和基礎(chǔ)設(shè)計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。</p><p>　　AASHTO荷載。 AASHTO規(guī)范第三部分總結(jié)了橋梁設(shè)計（上、下部結(jié)構(gòu)）要考慮的

48、荷載和作用力。主要有：恒載、活載、活載沖擊力或動力作用、風荷載以及其他荷載——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同樣認識到諸如活動支座處產(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)。</p><p>　　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。</p>

49、<p><b>　　永久作用</b></p><p>　　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。</p><p><b>　　可變作用</b></p><p>　　汽車荷載 小跨度橋梁的汽車荷載：