Unit 11 悬索桥

英语笔译实务（二级）

悬索桥

人们常常愿意修建悬桥以代替其他类型的桥梁，特别是在那些运输量比较小而桥的跨度又大的地方。因为悬桥不仅节约材料，而且强度也非常大。现在已经有了主跨超过3000英尺的悬桥，而整个桥面的重量都是由从河的两岸的桥塔悬挂下来的钢缆（一般只有两到四根）从上方来支持的。

钢缆由几千根具有很高抗拉强度的钢丝组成，这种钢丝均经过了电镀以防止锈蚀。这种钢丝每根直径0.19英寸左右，两三根夹紧扎在一起，成为一股钢丝绳，而整个钢缆可能是由相当数量的这样的钢丝绳紧密结合并用钢丝捆在一起而组成的。在制造钢缆时，可以采用两种不同的方法：一种是把钢丝绞合成股绳，然后再把这些股绳缠绕在中心股绳上面而形成完整的钢缆；另一种是把钢丝绳相互平行地编起来，然后每隔一段距离把它们夹在一起。后面这种办法显然需要涉及更长的编排操作，因为每根钢丝或每小股钢丝都必须加以编排，并且一股股一根根地调整到适当的下垂度。而绞合的钢丝股绳则可以作为整体一次性安装起来，只要它们不至于重得难以处理。但是相对大跨度的桥梁而言，用平行编排法编制钢缆也有某些优点。

钢缆一般是连续不断的，通过桥塔塔顶，向下穿过侧塔（在有侧塔的那些地方），然后再从侧塔，穿越过缆桩。钢缆支放在桥塔上专门建造的鞍座上，鞍座的形状造得适合钢缆使用。鞍座可以是固定的，这样钢缆可以在它上面滑动，也可以安装在滚柱上，这样鞍座就会随着钢缆的移动而移动。考虑到重型钢缆施加的巨大的拉力，它们的末端必须固定在牢固的缆墩上，而且除非钢缆末端埋置在坚固的天然岩石里，否则就必须建立圬工或混凝土桩，其强度要足以承受加在它上面的沉重的压力，钢缆股绳通常是绕套在股绳桩靴上，而桩靴又用键条连接到埋置在缆墩底部的锚定板上。

沿着主桥跨，每隔一段距离，就在钢缆上加上铸钢缆箍，紧紧地夹住钢缆，防止钢缆受潮，而且从缆箍悬下钢丝绳或链条组成的吊索。 由于这些吊索必须承受它们所连接的桥面的重量，因此它们必须具有很大的抗拉强度。之所以使用这种加固链条的吊索是因为它们大多可以省除加劲装置，因为这种吊索本身刚度很大。一般来说，防止桥面由于车辆货物的运动和风侧吹而变形是很有必要的。而在使用钢丝绳吊索的情况下，必须在桥面上建造桁架进行加劲。桁架的高度随桥跨的长度而定。

Suspension Bridges

Suspension bridges are frequently constructed in preference to other types of bridge, especially where relatively light traffic has to be carried over long spans, since they are more economical in material and are extremely strong. There are in existence suspension bridges with main spans of more than 3,000 feet, the entire weight of the deck being supported from above by cables (usually only two or four in number) suspended between two towers at either of the river.

The cables are composed of thousands of wires, made of high-tensile steel, which are galvanized to resist corrosion. Two or three hundred of these wires, each of about 0.19 inch in diameter, are clamped together to form a single strand, and the whole cable may consist of a considerable

英语笔译实务（二级）

number of such strands compacted and bound together with wire. In constructing the cable, two distinct methods may be adopted. The wires may either be twisted into strands, the strands then sometimes being twisted round a central strand to form the completed cable, or they may be spun parallel to each other, and clamped together at intervals. The latter method obviously involves a much longer spinning operation, since each wire or small group of wires must be spun and adjusted to the correct sag individually, whereas the strands of twisted wire can be erected as units, provided that they are not so heavy as to be unmanageable. However on bridges with very long spans, there are certain advantages in the parallel wire method of spinning the cable.

The cables are normally made continuous through the tops of the towers, down through side towers, where these exist, and thence into the anchorage. They bear on specially contructed saddles on the towers, which are shaped to accommodate them, the saddles being either fixed so that the cables may slide over them, or mounted on rollers so that they move with any movement of the cables. In view of the enormous pull exerted by the heavy cables, their ends must be secured in firm anchorages, and unless they can be embedded in sound natural rock, constructions of masonry or concrete must be provided strong enough to withstand the severe pressures put upon them. The cable strands are normally looped round strand-shoes, which are in turn connected by chains to an anchor-plate embedded in the base of the anchorage.

At intervals along the main span, cast-steel cable bands are attached to the cables, gripping them firmly and excluding moisture from them, and from these bands suspenders of wire-rope or chains hang down. Since these suspenders have to take the weight of the deck to which they are attached, they must have high tensile strength. One advange of using the brace-chain suspenders is that they largely dispense with the need for a system of stiffening, being themselves rigid. This stiffening is necessary to resist deformations of the deck of the bridge due to moving traffic loads and also to resist lateral pressures from wind. In the case of wire-rope suspenders, the stiffening must be provided by trusses constructed at the level of the deck, the depth of the truss varying with the length of the span.

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