【正文】 loading ,design ,and construction requirements of the AASHTO requirements for pedestrian crossings and bridges serving other purposes may be established by local or regional codes and Code provisions are often incorporated by spans to about 100ft often consist of precast integraldeck units ,which offer low initial cost ,minimum ,maintenance ,and fast easy construction ,with minimum traffic girders are generally units are placed side by side ,and are often posttensioned laterally at intermediate diaphragm locations ,after which shear keys between adjacent units are filled with nonshrinking highway spans ,an asphalt wearing surface may be applied directly to the top of the precast some cases ,a castinplace slab is placed to provide posite voided slabs are monly available in depths from 15 to 21 widths of 3 to 4 a standard highway HS20 loading, they are suitable for spans to about 50 ft, Standard channel sections are available in depths from 21 to 35 in a variety of widths, and are used for spans between about 20 and 60 hollow box beamsand singletee girders are intended for longer spans up to about 100 mediumspan highway bridges ,to about 120 ft ,AASHTO standard I beams aregenerally are intended for use with a posite castinplace roadway girders often bine pretensioning of the precast member with posttensioning of the posite beam after the deck is an effort to obtain improved economy ,some states have adopted more refined designs ,such as the State of Washington standard specially designed precast girders may be used to carry a monorail transit finished guide way of Walt Disney World Monorail features a series of segments, each consisting of six simply supported pretensioned beams ,together to from a continuous spans are 100 to 110 half of the 337 beams used have some bination of vertical and horizontal curvatures and variable super beams are hollow, a feature achieved by inserting a styrofoam void in the curved beams and by a moving mandrel in straight beam girders may not be used for spans much in excess of 120 ft because of the problems of transporting and erecting large, heavy the other hand ,there is a clear trend toward the use of longer spans for elevated urban expressways ,long spans facilitate access and minimize obstruction to activities for environmental damage has led to the choice of long spans for continuous river crossings, intermediate piers may be impossible because of requirements of navigational typical construction of this type, piers are castinplace, often using the slipforming ―hammerhead‖ section of box girder is often cast at the top of the pier, and construction proceeds in each direction by the balanced cantilever , after the closing castinplace joint is made at midspan, the structure is further posttensioned for full keys may be used on the vertical faces between segments, and precast are glued with epoxy imaginative engineering demonstrated by many special techniques has extended the range of concrete construction for bridges far beyond anything that could be conceived just a few years the United States, twin curved castin –place segmental box girders have recently been pleted for of span of 310 ft over the Eel River in northern design has been pleted for twin continuous box girders consisting of central 550 ft spans flanked by 390 ft side form of prestressed concrete bridge well suited to long spans is the cablestayed box notable example is the ChacoCorrientes Bridge in bridges main span of 804 ft is supported by two Aframe towers, with cable stays stretching from tower tops to points along the deck itself consists of two parallel box girders made of precast sections erected using the cantilever tensioned cables not onlyprovide a vertical reaction ponent to support the deck ,but also introduce horizontal pression to the box girders ,adding to the posttensioning force in those Bridge pioneered many years ago by the German engineer Ulrich stressribbon bridge carries a pipeline and pedestrians over the Rhine River with a span of 446 superstructure erection sequence was to(a)erect two pairs of cables,(b)place precast slabs forming a sidewalk deck and a U under each of the sets of cables, and(c)castinplace concrete within the two pipeline is placed atop supports at railing height, off to one side, which greatly increases the wind speed of the is appropriate in discussing bridge forms to mention structural time is past when structures could be designed on the basis of minimum cost and technical advantages structures in particular are exposed for all to produce a structure that is visually offensive ,as has occurred all too often in the past, is an act professional for major spans ,but also for more ordinary structures ,architectural advice should be sought early in conceptual stage of the design process.第二篇：橋梁混凝土結(jié)構(gòu)耐久性施工方案《橋梁混凝土結(jié)構(gòu)耐久性施工方案》一、編制說(shuō)明根據(jù)施工設(shè)計(jì)圖提供技術(shù)參數(shù)及資料，本工程地處多為鹽堿和鹽堿水環(huán)境，其地質(zhì)多為海相沉積形成，富含ClSO2等多種離子。當(dāng)結(jié)構(gòu)可能根據(jù)最小的費(fèi)用和技術(shù)設(shè)計(jì)的時(shí)候，時(shí)間消逝了。壓帶是橋運(yùn)輸跨越萊茵河的一個(gè)管道和人行道，跨徑446英尺。一個(gè)值得注意的例子是阿根廷境內(nèi)的ChacoCorrientes橋。想象的工程學(xué)藉著許多特別的技術(shù)示范已經(jīng)延長(zhǎng)混凝土建筑的范圍，就橋梁而言，已經(jīng)遠(yuǎn)遠(yuǎn)超過(guò)幾年以前可以想象的到的任何事。在這一個(gè)類型的典型建筑中，橋墩（臺(tái)）采用現(xiàn)場(chǎng)預(yù)制, 經(jīng)常使用滑動(dòng)的技術(shù)。另一方面，橋梁有一種向大跨徑發(fā)展的明顯趨勢(shì)。典型的跨距是100到110英尺。在板被安置之后，這樣的梁經(jīng)常在預(yù)澆梁的先張拉 與合成梁的后張拉后結(jié)合。標(biāo)準(zhǔn)渠化區(qū)段在多種寬度，深度從21英尺到35英尺時(shí)是有利的，可用于大約20英尺到60英尺的跨徑。對(duì)于公路，用瀝青鋪設(shè)的表面可以直接用在預(yù)制混凝土的上面。ACI代碼的備注也被納入?yún)⒖?。采用預(yù)制、現(xiàn)場(chǎng)澆筑或兩種方法并用。從使用標(biāo)準(zhǔn)組成的小跨徑橋梁到吊梁和跨徑將近100英尺的連續(xù)箱梁橋，幾乎所有的混凝土橋梁，甚至于相對(duì)短時(shí)間的橋梁都是預(yù)應(yīng)力結(jié)構(gòu)的。對(duì)于服務(wù)于其它目的步行街和橋梁的設(shè)計(jì)要求由當(dāng)?shù)氐幕虻胤降拇a建立。預(yù)制板一塊挨一塊的放置并且在相鄰的預(yù)制板間受剪的縫隙填滿不收縮的灰泥之后，經(jīng)常在中間橫膈膜的位置后張拉。對(duì)于一個(gè)標(biāo)準(zhǔn)HS20的公路，空心板適合于大約50 英尺的跨徑。它們和一種復(fù)合現(xiàn)場(chǎng)預(yù)制行車道板一起使用。完成的沃爾特迪斯尼樂(lè)園單軌鐵路的一系列的特征, 每個(gè)包括六個(gè)單獨(dú)支持的預(yù)拉梁，一起形成連續(xù)結(jié)構(gòu)。由于運(yùn)輸問(wèn)題和構(gòu)件垂直的大而重的問(wèn)題，預(yù)制梁不能用于跨徑超過(guò)120英尺的橋梁。對(duì)于跨河橋，因?yàn)楹叫虚g隙的需求，中間可能不可以搭設(shè)橋墩。修剪鑰匙可能被用在片段之間垂直面之上, 而且預(yù)制建筑與環(huán)氧基樹(shù)脂黏在一起。預(yù)應(yīng)力混凝土橋梁很適合于大跨徑的另一種形式是懸索箱梁。許多年以前德國(guó)工程師 Ulrich Finsterwalder 提出適合于負(fù)擔(dān)荷載和大跨徑的一個(gè)結(jié)構(gòu)類型是壓帶式橋。討論橋梁形式應(yīng)適當(dāng)?shù)目紤]結(jié)構(gòu)的美學(xué)。特別地對(duì)于主要的跨距，還有一些比較普通的結(jié)構(gòu)來(lái)說(shuō)，應(yīng)該在設(shè)計(jì)過(guò)程的概念階段尋找建筑的建議。二、根據(jù)混凝土防腐設(shè)計(jì)設(shè)計(jì)圖依據(jù)工程施工規(guī)范標(biāo)準(zhǔn)：《普通混凝土配合比設(shè)計(jì)規(guī)程》JGJ552011）《公路工程混凝土結(jié)構(gòu)防腐技術(shù)規(guī)范》（JIC/TB07012006）《混凝土結(jié)構(gòu)工程施工質(zhì)量驗(yàn)收規(guī)范》(GB50