【正文】 ure of Concrete Bridge Prestressed concrete has proved to be technically advantageous, economically petitive, and esthetically superior bridges, from very short span structures using standard ponents to cablestayed girders and continuous box girders with clear spans of nearly all concrete bridges, even those of relatively short span, are now , castinplace construction, or a bination of the two methods may be pretensioning and post tensioning are employed, often on the same the United States, highway bridges generally mustmeet 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。生產(chǎn)視覺上不愉快的結(jié)構(gòu) , 過去經(jīng)常發(fā)生, 是一種不負(fù)專業(yè)責(zé)任的行為。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)的時候，時間消逝了。放置在頂部的管道支撐在扶手的頂部，向一邊傾斜，大幅地增加結(jié)構(gòu)的主要風(fēng)速。壓帶是橋運(yùn)輸跨越萊茵河的一個管道和人行道，跨徑446英尺。受拉的懸索不僅提供一種垂直反應(yīng)組成支撐底板，而且對于箱梁產(chǎn)生水平的壓縮，增加構(gòu)件中的張拉力。一個值得注意的例子是阿根廷境內(nèi)的ChacoCorrientes橋。該橋的中間跨度550英尺，側(cè)跨跨度390英尺，初步設(shè)計(jì)已經(jīng)完成。想象的工程學(xué)藉著許多特別的技術(shù)示范已經(jīng)延長混凝土建筑的范圍，就橋梁而言，已經(jīng)遠(yuǎn)遠(yuǎn)超過幾年以前可以想象的到的任何事。最后,在完成跨中結(jié)合處的澆筑之后, 這種結(jié)構(gòu)對于完全連續(xù)性的橋梁來說是進(jìn)一步的受拉的。在這一個類型的典型建筑中，橋墩（臺）采用現(xiàn)場預(yù)制, 經(jīng)常使用滑動的技術(shù)。對環(huán)境的損害問題的關(guān)心，導(dǎo)致連續(xù)高架橋大跨徑的選擇。另一方面，橋梁有一種向大跨徑發(fā)展的明顯趨勢。所有的梁是中空的，它的特征是通過在曲梁中插入泡沫