专业英语-Lesson-18-Bridge-and-Alignment.docx

Lesson 18 Bridge and AlignmentBridges are great symbols of mankinds conquest of space. The sight of the crimson（深红色的） tracery (装饰的图案、花纹)of the Golden Gate Bridge against a setting sun in the Pacific Ocean, or the arch of the Gambit Viaduct（高架桥） soaring（高飞、翱翔） triumphantly （成功的、获胜的）above the deep gorge(深谷), fills ones heart with wonder and admiration for the art of their builders.当看到太平洋上深红色的金门大桥映照在日落的黄昏中时，或者看到加拉比高架拱桥从深谷中腾空而起时，人们一定感到神奇，并充满对建设者艺术创造力的崇拜。They are the enduring （持久的）expressions （表达、表示）of mankinds determination to remove all barriers （障碍物）in its pursuit（追求、追逐） of a better and freer world. Their design and building schemes（安排、设计） are conceived in dream-like visions（视力、想象力）. But vision and determination are not enough. 这些桥梁是人类在追求一个更美好更自由的世界的过程中排除一切障碍的决心的永久印证。它们的设计和施工技术令人们如梦如幻。但是梦想和决心并不够。All the physical forces of nature and gravity must be understood with mathematical precision （精确、正确）and such forces have to be resisted by manipulating（熟练地使用） the right materials in the right pattern. This requires both the inspiration（灵感） of an artist and the skill of an artisan（工匠）.所有自然界的力和重力必须采用数学方式精确计算，并且采用适当的材料和适当的结构来承担。All the physical forces of nature and gravity must be understood with mathematical precision （精确、正确）and such forces have to be resisted by manipulating（熟练地使用） the right materials in the right pattern. This requires both the inspiration（灵感） of an artist and the skill of an artisan（工匠）.所有自然界的力和重力必须采用数学方式精确计算，并且采用适当的材料和适当的结构来承担。Scientific knowledge about materials and structural behaviour（结构性能） has expanded(扩大；展开) tremendously（极大的、巨大的）, and computing techniques are now widely available to manipulate （熟练地使用） complex theories in innumerable（无数的） ways very quickly. 关于材料和结构性能的科学技术已经得到巨大发展，计算技术现在也可以很快的应付复杂的理论计算。Engineers have virtually revolutionized bridge design and construction methods in the past decade. The advances apply to short-（小跨径桥梁）, medium, and long-span bridges.在过去的十年，工程师使桥梁设计和施工方法发生了革命性的变化。这些进步应用于小跨、中跨和大跨桥梁。For permanent（永久的） bridges, the most commonly used materials are steel and concrete. Bridges of many different types are built with these materials, used singly or in combination. Timber（木材） may be used for temporary above-water construction, for the elements of a structure that lie below the waterline (particularly timber piles桩), or for short-span bridges located on secondary roads(次要道路). A few short-span aluminum（铝） bridges have been built in the United States on an experimental basis.木材可能用于水上临时性构造物，水位线以下的结构构件或者次要道路上的小跨径桥梁。几座实验性的小跨径铝桥已经在美国建成。 The principal （主要的、首要的）portions of a bridge may be said to be the “substructure” （下部结构）and “superstructure”（上部结构）. This division is used here simply for convenience, since in many bridges there is no clear dividing line between the two.Common elements of the substructure are abutments (usually at the bridge ends)(桥台) and piers (between the abutments)（桥墩）. Piers and abutments often rest on separately constructed foundations such as concrete spread footings (扩大基础)or groups of bearing piles（承重桩）; these foundations are part of the substructure. 桥墩和桥台放在单独修建的基础上，比如扩大基础或群桩；这些基础是下部构造的一部分。Occasionally（偶尔的、偶然的） a bridge substructure comprises（由组成） a series of pile bents （桩排架）in which the piles extend above the waterline and are topped by a pile cap（承台） that, in turn, supports the major structural elements of the superstructure. Such bents often are used in a repetitive（重复的、反复的） fashion as part of a long, low, over-water crossing.桥梁下部结构有时也由一组排架组成，这些排架露出水面，在上面有承台，由承台支撑桥的上部结构。这种排架一般采用相同的结构形式，作为又长又低的水上桥跨的一部分。In recent years, the dividing lines between short, medium, and long-span bridges have blurred（使模糊不清） somewhat. Currently, spans of 20 to 100 ft (6.1 to 30.5 m) are regarded as short by many designers, who have developed many standardized （使标准化）designs to handle these spans economically. Medium spans range up to, perhaps, 400 ft (121.9 m) in modern bridge practice, depending on the organization（结构） involved and the materials used. Long spans range up 4000 ft (1219.2 m) or more, but a clear span above 1000 ft (304.8m) is comparatively（比较而言的） rare.Bridges may also be classed as “deck” or “through” type（上（下）承式）. In the deck type of bridge （上承式桥梁）, the road way is above the supporting structure, that is, the load carrying elements of the superstructure are below the roadway. 上承桥是桥面在支撑结构的上面，即上部结构的支撑物在桥面以下。In the through type of bridge(下承式), the roadway passes between the elements of the superstructure, as in a through steel truss (桁架)bridge. Deck structures predominate（优点）: they have a clean appearance（外观简洁）, provide the motorist with a better view of the surrounding area, and are easier to widen if future traffic requires it.下承式桥梁是桥面在上部结构物之间穿过，比如下承式钢桁架桥。下承式桥梁的优点是：外表简洁，视野开阔，以及容易加宽，以满足远期交通的需要。Examples of short-span concrete bridges include cast-in-place（现浇）, reinforced concrete （钢筋混凝土）T beam (and slab)；simple-span（单跨）, prestressed which incorporates precast, prestressed I girders or box girders topped by a cast-in-place deck; and cast-in-place box girder（箱梁）.混凝土小跨径桥的形式包括现浇T形梁（及板）；单跨预应力桥（包括预制预应力I形梁或者箱形粱，顶部为现浇的桥面）；以及现浇箱形粱。The designer of each medium-and long-span bridge tries to devise（想出、设计） a structure that is best suited to the conditions encountered（遭遇、遇到） at that particular location. The result is an almost bewildering （使迷惑、使混乱）variety of structures that differ either in basic design principle or in design details.每一座中桥和长跨桥的设计者尽量优化设计结构以使桥梁最好地适应当地的特殊条件；结果出现了众多不同形式的桥梁，它们或者在设计原则上或者是在细部设计上不同。Plate girders are used in the United States for medium spans. They generally are continuous structures with maximum depth of girder over the piers（桥墩） and minimum depth at midspan. The plate girders generally have an I cross section（ I 形断面）; they are arranged in lines that support stringers（桁架）, floorbeams, （桥面）横梁）and, generally, a cast-in-place concrete deck（现浇桥面）. 板梁一般为I形断面，它们排成一行以支撑桁架、横梁还有现浇桥面。The girders are shop-fabricated （建造、装配）by welding; field connections generally are by high-strength bolts（高强螺栓）. Welded-steel box girder structures （焊接钢箱梁）are generally similar to plate girder spans except for the configuration（形状、外形） of the bridge cross section.梁通过焊接在车间装配；现场的连接通常使用高强螺栓。Rigid frames （刚架）are used occasionally（偶然的）, most often for spans in range of 23 to 30 m (75 to 100 ft) and for grade-separation structures（立体交叉构造物）. Arch bridges are used for longer spans at locations where intermediate piers cannot be used and where good rock is available to withstand the thrusts（推力） at the arch abutments（桥台）. 拱桥用在跨度较大，中间不能设置桥墩的地方，岩石条件要好以承受桥台处的水平推力。A variation in the arch bridge is the tied arch（系杆拱）, in which a horizontal tie （水平系杆） that carries the roadway takes much of the horizontal thrust inherent （内在的、固有的）in the arch form.系杆拱是拱桥的变形形式，支撑桥面的水平系杆承担了拱桥结构的大部分水平推力。Cable-stayed bridges are specially suited in the span range of 200 to 500 m and thus provides a transition between the continuous box girder bridge and the stiffened（加劲、加强） suspension cable. 斜拉桥尤其适用于跨径在200m到500m的桥梁，因此是连续箱梁和加劲悬索桥的过渡形式。The cab