大型桥梁及施工外文翻译--大跨度桥梁

Large Span Bridge

1.Suspension Bridge

The suspension bridge is currently the only solution in excess of 600 m, and is regarded as competitive for down to 300. The world’s longest bridge at present is the Verrazano Narrows bridge in New York. Another modern example is the Severn Bridge in England.

The components of a suspension bridge are: (a) flexible cables, (b) towers, (c) anchorages, (d) suspenders, (e) deck and ，(f) stiffening trusses. The cable normally consists of parallel wires of high tensile steel individually spun at site and bound into one unit .Each wire is galvanized and the cable is cover with a protective coating. The wire for the cable should be cold-drawn and not of the heat-treated variety. Special attention should be paid to aesthetics in the design of the rowers. The tower is high and is flexible enough to permit their analysis as hinged at both ends. The cable is anchored securely anchored to very solid anchorage blocks at both ends. The suspenders transfer the load form the deck to the cable. They are made up of high tensile wires and are normally vertical. The deck is usually orthotropic with stiffened steel plate, ribs or troughs，floor beam, etc. Stiffening trusses, pinned at the towers, are providing. The stiffening system serves to control aerodynamic movements and to limit the local angle changes in the deck. If the stiffening system is inadequate, torsional oscillations due to wind might result in the collapse of the structure, as illustrated in the tragic failure in 1940 of the first Tacoma Narrows Bridge.

The side span to main span ratio varies from 0.17 to 0.50 .The span to depth ratio for the stiffening truss in existing bridge lies between 85 and 100 for spans up to 1,000m and rises rather steeply to 177. The ratio of span to width of deck for existing bridges ranges from 20 to 56. The aerodynamic stability will have be to be investigated thoroughly by detailed analysis as well as wind tunnel tests on models.

2.The cable-stayed bridge

During the past decade cable-stayed bridges have found wide application, s\especially in Western Europe, and to a lesser extent in other parts of the world.

The renewal of the cable-stayed system in modern bridge engineering was due to the tendency of bridge engineering in Europe, primarily Germany, to obtain optimum structural performance from material which was in short supply-during the post-war years.

Cable-stayed bridges are constructed along a structural system which comprises an

orthotropic deck and continuous girders which are supported by stays, i.e. inclined cables passing over or attached to towers located at the main piers.

The idea of using cables to support bridge span bridge span is by no means new, and a number of examples of this type of construction were recorded a long time ago. Unfortunately the system in general met with little success, due to the fact that the statics were not fully understood and that unsuitable materials such as bars and chains were used to form the inclined supports or stays. Stays made in this manner could not be fully tensioned and in a slack condition allowed large deformations of the deck before they could participate in taking the tensile loads for which they were intended.

Wide and successful application of cable-stayed systems was realized only recently, with the introduction of high-strength steels, orthotropic decks, development of welding techniques and progress in structural analysis. The development and application of electronic computers opened up new and practically unlimited possibilities for exact solution of these highly statically indeterminate systems and for precise stoical analysis of their three-dimensional performance.

Existing cable-stayed bridges provide useful data regarding design, fabrication, erection and maintenance of the mew system. With the construction of these bridges many basic problems encountered in their engineering are shown to have been successfully solved. However, these important data have apparently never before been systematically presented.

The application of inclined cable gave a new stimulus to construction of large bridges. The importance of cable-stayed bridges increased rapidly and within only one decade they have become so successful that they have taken their rightful place among classical bridge system. It is interesting to note now how this development which has so revolutionized bridge construction, but which in fact is no new discovery, came about.

The beginning of this system, probably, may be traced back to the time when it was realized that rigid structures could be formed by joining triangles together. Although most of these earlier designs were based on sound principles and assumptions, the girder stiffened by inclined cables suffered various misfortunes which regrettably resulted in abandonment of the system. Nevertheless, the system in itself was not at all unsuitable. The solution of the problem had unfortunately been attempted in the wrong way.

The renaissance of the cable-stayed, however, was finally successfully achieved only