毕业设计(论文)外文资料翻译系 别： 专 业： 班 级： 姓 名： 学 号： 外文出处： 土木工程网 附 件： A.英文文献； B. 译文 2014年6月1日附录A英文文献BridgesBridges are great symbols of mankinds conquest of space. The sight of the crimson tracery of the Golden Gate Bridge against a setting sun in the Pacific Ocean, or the atch of the Garabit Biaduct soaring triumphantly above the deep gorge. Fills ones heart with wonder and admiration for the art of their builders11. They are the enduring expressions of mankinds determination to remove all barriers in its pursuit of a better and freer world. Their design and building schemes are conceived in dream-like bisions. But vision and determination are not enough. All the physical forces of nature and gravity must be understood with mathematical precision and such forces have to be resisted by manipulating the right materials in the right pattern. This requires both the inspiration of an artist and the skill of an artisan.Scientific knowledge about materials and structural behavior has expanded tremendously, and computing techniques are now widely available to manipulate complex theories in innumerable ways very quickly. Engineers have virtually revolutionized bridge design and construction methods in the past decade. The advances apply to short-medium and long-span bridges.For permanent bridge，the most commonly used materials are steel and concrete. Bridge of many different type are built with these materials, used singly or in combination. Timber may be used for temporary above-water construction, for the elements of a structure that lie below the waterline (particularly timber pile s), or for short-span bridges located on secondary roads. A few short-span aluminum bridges have been built in the United States on an experimental basis.The principal portions of a bridge may be said to be the “substructure” and the “superstructure.” This division is used here simply for convenience, since in many bridges there is no clear dividing lint between the two.Common elements of the substructure are abutments (usually at the bridge ends) and piers (between the abutments).Piers and abutments often rest on separately constructed foundations such as concrete spread footings or groups of bearing piles; these foundations are part of the substructure. Occasionally a bridge substructure comprises a series of pile bents in which the piles extend above the waterline and are topped by a pile cap that, in turn, supports the major structural elements of the superstructure. Such bents often are used in arepetitive fashion as part of along, low, over-water crossing.In recent years, the dividing lines between short-medium and long-span bridge have blurred somewhat. Currently, spans of 20 to 100 ft (6.1 to 30.5m) are regarded as short by many designers, who have developed many standardized designs to handle these spans economically. Medium spans range up to, per-haps, 400ft (121.9m) in modern bridge practice, depending on the organization involved and the materials used. Long spans range up to 4000ft (1219.2m) or more, but a clear span above 1000ft (304.8m)is comparatively rare.In the United States, highway bridges generally must meet loading, design, and construction requirements of the AASHTO Specification. The design and construction of railway bridges are governed by provisions of the AREA Manual for Railway Engineering. Design requirements for pedestrian crossings and bridges serving other purposes may be established by local or regional codes and specifications. ACI Code provisions are often incorporated by reference, and in most cases serve as model provisions for other governing documents.Bridge spans to about 100 ft often consist of pre-cast integral-deck units. These units offer low initial cost, minimum maintenance, and fast easy constrction, with traffic interruption. Such girders are generally pretensioned, the units are placed side by side, and are often post-tensioned laterally at intermediate diaphragm lacations, After which shear keys between adjacent units are filled with non-shrinking mortar. For highway spans, an asphalt wearing surface may be applied directly to the top of the pre-cast concrete. In some cases, a cast-in-place slab is placed to provide composite action.For medium-span highway bridges, to about 120 ft, AASHTO standard I beams are generally used. he are intended for use with a composite cast-in-place roadway slab. Such girders often combine pre-tensioning of the pre-cast member with post-tensioning of the composite beam after the deck is placed.Pre-cast girders may not be used for spans much in excess of 120 ft because of the problems of transporting and erecting large, heavy units. On the other hand, there is a clear trend toward the use of longer span