8 Bridge Design and Construction 桥的设计与建造1. New words analysisaccessory= access(increased)oryDerrick=from Derrick, the surname of a London hangmanDebris=orign early 18th cent.: from French dbris, from obsolete dbriser break downPlanning. The first step leading to the construction of a modern major bridge is a comprehensive study to determine whether a bridge is needed.规划设计 现代重要的桥梁建造的第一步是广泛地 研究以确定桥梁的必要性。 If it is to be a highway bridge, in the United States for example，a planning study is initiated by a state bridge authority，possibly in cooperation with local government or the federal government .比如：如果是美国的高速公路桥，是由州桥管理 局研究规划并确定，同时当地的政府或联邦政府 一起参与。Studies are made to estimate the amount of bridge traffic, the relief of jammed traffic in nearby highway network, the effects on the regional economy, and the cost of the bridge.桥梁的交通流量、对附近高速公路网交通堵塞的调剂， 对当地经济的影响和桥的造价等因素进行评估研究。 The means for financing the project, such as public taxes or sale of revenue bonds repaid by toll charges, are considered. Bond n.结合(物), 粘结(剂), 联结, 公债, 债券, 合同 revenue bond收益债券 这就决定了工程的投资方式，如公众收费，依靠过 通行费来支付的发行债券的规模都要被考虑进来。 If the studies lead to a decision to go ahead with the project, the land needed for the bridge and its approaches is acquired at the selected site.如果研究认为其可行信，那么桥选址和占地问题将 着手处理。At this point, field engineering work is started. Accurate land surveys are made. land survey 土地测量在确定场地时，现场测绘工作开始进行，做好精 确的实地测量。Tides, flood conditions，currents, and other characteristics of the waterway are carefully studied.潮汐，洪水因素，水流和排水的其它的特征都要 仔细研究，Boring samples of soil and rock are taken at possible foundation locations, both on land and under the water. 在陆地和水下的泥土和岩石的钻孔取样在基础可 能的位置都要尽可能地进行。Selection of bridge design.桥梁设计类型的选择 The chief factors in deciding whether a bridge will be built as a girder , cantilever , truss , arch , suspension , or some other type are： (1) location；for example, cross a river ;(2)purposes ; for example , a bridge for carrying motor vehicles ; ( 3 ) span length ; ( 4 ) strength of available materials ; ( 5 ) cost ; ( 6 ) beauty and harmony with the location .决定把桥建成梁、悬臂、桁架、拱、悬索或其他类 型结构的主要因素是：（1）地点，如跨越河流；（2 ）目的，如建桥为了方便交通；（3）跨度；（4）可 用材料强度；（5）花费；（6）美观和和谐性。Each type of bridge is most effective and economical only within a certain range of span lengths, as shown in the following table: . 每种结构类型的桥，只有在一定跨度范围内，才 能是最经济和最有效。如下表所示： 桥桥的类类 型最佳跨度英尺米梁桥桥20到10006.1到 304.8 刚刚架桥桥80到30024.4到 91.4 拱桥桥200到 100061.0到 304.8 桁架桥桥200到 140061.0到 426.7 悬悬臂桥桥500到 1800152.4到 548.6 悬悬索桥桥1000到 5000304.8到 1524.0As indicated in the table , there is a considerable overlap in the range of applicability of the various typesIn some cases，alternative preliminary designs are prepared for several types of bridge in order to have a better basis for making the final 上表表明了不同结构类型的适用性有很多交叉的地方 。在一些实例中，在不同的初步设计中，用来比较不 同类型的桥是为了在最后有最好的选择。Selection of materials材料的选择 The bridge designer can select from a number of modern high-strength materials，including concrete， steel，and a wide variety of corrosion-resistant alloy steels桥梁设计者能选用大量的现代高强材料，包括混泥土 、钢筋和多种耐腐蚀的合金钢。 For the Verrazano-Narrows Bridge，for example ，the designer used at least seven different kinds of alloy steel，one of which has a yield strength of 5000 pounds per square inch(psi)(3，515 kgsq cm) and does not need to be painted because an oxide coating forms on its surface and inhibits corrosioninhibit 抑制, 约束, 化医抑制拿Varian-Narrows大桥来说，设计者使用了七种不同 的合金钢，其中之一的合金的屈服强度为50000英镑每 平方英寸（3115kg/c）,而且不需要油漆保护，因为 有一种氧化膜覆盖在它的表面而防止腐蚀。The designer also can select steel wires for suspension cables that have tensile strengths up to 250，000 psi(17 ，577 kgsq cm)设计者还选用钢丝绳作为悬索，它的抗拉强度超过 250000英镑每平方英寸（17577 kg/c）Concrete with compressive strengths as high as 8,000 psi (5625 kgsq Cm) can now be produced for use in bridges , and it can be given high durability against chipping and weathering by the addition of special chemical agents and control of the hardening process . chipping 碎屑；小碎片 weathering侵蚀,风化现在，抗压强度高达8000英镑每平方英尺（ 562.5kg/c）的混泥土被生产用于桥梁工程，而 且它在增加特殊化学物质后具有很高的抗脆裂性 能和抗风化性能， Concrete that has been presressed and reinforced with steel wires has a tensile strength of 250,000psi ( 17,577 kg / sq cm).用钢绞线加强的预应力混凝土，其强度达到 250000英镑每平方英寸（17577 kg/c）Other useful materials for bridges include aluminum alloys and wood. 桥梁使用的其它材料还有铝合金和木材。Modern structural aluminum alloy have yield strengths exceeding 40,000 psi(2,812 kg/sq cm). 现在的铝合金的屈服强度超过了40000每平方英寸（ 2818 kg/c）。Laminated strips of wood glued together can be made into beams with strengths twice that of natural timber; glue-laminated southern pine, for example, can bear working stresses approaching 30, 000 psi(210.9 kg/sq cm).laminated由薄片叠成的把片状的木条粘在一起做成的梁是自然木材强度的二 倍。例如用南部松树而胶结的梁能承受的工作应力达到 了3000英镑每英寸（210.9 kg/c）。 Analysis of forces力的分析A bridge must resist a complex combination of tension, compression, bending, shear, and torsion forces.一座桥要抵抗一系列的合力，如拉