土木工程专业英语(武汉理工大学出版社)lesson8.ppt

8 Bridge Design and Construction 桥的设计与建造,1. New words analysis accessory= access(increased)ory Derrick=from Derrick, the surname of a London hangman Debris=orign early 18th cent.: from French dbris, from obsolete dbriser break down,Planning. 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：,As 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 corrosion inhibit 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，如拉力，压力，剪力和扭力。 In addition, the structure must provide a safety factor as insurance against failure. 另外，结构还需要一定的安全系数作为防止破坏的安全储备。 The calculation of the precise nature of the individual stresses and strains in the structure, called analysis, is perhaps the most technically complex aspect of bridge building. 对结构的各种应力和应变的准确特性进行计算，这就叫应力分析，这或许是桥梁结构中最复杂的技术。 The goal of analysis is to determine all of the forces that may act on each structural member. 应力分析的目的是为了确定作用在结构上的各种力。,The forces that act on bridge structural members are produced by two kinds of loads-static and dynamic. 作用在桥梁结构的力都可以分为二类荷载：动荷载和静荷载。 The static load - the dead weight of the bridge structure itself -is usually the greatest load. The dynamic, or live, load has components, including vehicles carried by the bridge, wind forces, and accumulations of ice and snow. 静荷载即桥的自重它往往也是最大的荷载。动荷载或静荷载有很多，包括桥面上的机动车，风荷载，和积冰积雪荷载。,Although of the total weight of the vehicles moving over a bridge at any time is generally a small fraction of the static and dynamic load, it presents special problems to the bridge designer because of the vibration and impact stresses created by moving vehicles. 虽然随时在桥面上移动的车辆的总重量相对于静荷载和动荷载来说是一个很少的部分，而对设计者来说，因为机动车辆产生的振动和冲击压力而会出现特殊问题。 For example, the severe impacts caused by irregularities of vehicle motion or bumps in the roadway may momentarily double the effect of the live load on the bridge. 例如：在路面上机动车的不规则的运动或碰撞对桥面产生瞬时双倍活荷载的作用力。,Wind exerts force on a bridge both directly by striking the bridge structure and indirectly by striking vehicles that are crossing the bridge. 风在桥上的作用的力包括： 直接作用桥结构的力和间接的通过作用在通行车辆的力。 If the wind induces aero elastic vibration, as in the case of the Tacoma Narrows Bridge, its effect may be greatly amplified. 如果出现空气弹性振动，在这种情况下的Tacoma Narrows大桥的风作用被大大地增大， Because of this danger, the bridge designer makes provisions for the strongest winds that may occur at the bridge location. provision n. 供应, 提供, 供给，准备, 防备；食物和饮料规定, 条款, 条件 由于这种危险的存在，桥的设计者必须知道桥址处可能发生的最大的风。 Other forces that may act on the bridge, such as stresses created by earthquake tremors, must also be provided for. 还有其它的力作用在桥上，如：地震产生的压力也必须注意。,Special attention must often be given to the design of the bridge piers, since heavy loads may be imposed on them by currents, waves, and floating ice and debris. Occasionally a pier may even be hit by a passing hip. 对桥墩的设计要给予特殊的关注，因为桥墩承担水流，浮冰和漂浮物而产生的重荷载，桥墩通常还有被船撞击的可能。,Electronic computers are playing an ever increasing role in assisting bridge designers in the analysis of forces. 电脑在力分析上协助桥梁设计者，起着很重要的作用。 The use of precise model testing, particularly for studying the dynamic behavior of bridges, also helps designers. 用一个精确的模型试验，尤其对桥的动力的活动状态的研究也可以帮助设计者。 A scaled-down model of the bridge is constructed, and various gauges to measure strains, accelerations, and deformations are placed on the model. 一个缩尺比例的桥模结构中，布置很多位移计对桥模各处的应力，加速度和变形进行测量。,The model bridge is then subjected to various scaled-down load or dynamic condition to find out what will happen. 桥模在同样比例的荷载和动力条件作用下，来分析桥的受力行为。 Wind tunnel tests may also be made to ensure that nothing like the Tacoma Narrows Bridge failure can occur. With modern technological aids, there is much less chance of bridge failure than in the past. 风洞试验也可以确保不再发生Tacoma Narrows大桥的失败。在现代技术的帮助下，桥梁事故出现的机会将大大少于以前。,Construction the foundations. 基础 施工 Construction starts with the foundation， which may cost almost as much as the superstructure . 施工都是从基础开始的，基础的花费几乎大大超过上层建筑。 Foundations built in water usually present the greatest difficulties. One of the older methods, which is still used in shadow waters, is to erect cofferdams similar to the ring of closely spaced piles that the Romans used. 水下基础通常会遇到很大的困难，有个古老的方法常被用于浅水中，即在小范围内布置垂直围堰而建桥墩。罗马人常用这种方法。,For constructing foundations in deep water, caissons have long been used . 在深水中建基础一般用沉箱法。 the caisson, which is a huge box closed on all sides except the bottom, is lowered onto the river bed. 沉箱是一个底部开口其余封闭的大盒子而沉入河床上， Workers inside the caisson, , which is filled with compressed air to keep out the water, dig deeper and deeper, and the caisson sinks as the digging proceeds , When a suitable depth is reached，the caisson is filled with concrete and becomes part of the foundation itself . 工人们在为挡水而充满压缩空气的沉箱里，越挖越深，沉箱也跟着下沉。当达到合适的深度后在箱内填入混泥土而成为基础的一部分。,Another deep-water method, less hazardous and less costly than the caisson method, uses steel or concrete piles. 在深水中建基础的另一种方法比沉箱法更安全和更低的成本，用于钢或混泥土桥墩。 With modern pile drivers, long heavy piles can be driven even In deep water. 用现代的打桩机，长重桩可以打入深水中。 The piles can be cut off and capped either above the water level or below it. 桩可以在水面或水下截断或做成桩帽。 If they are capped below the water level, a prefabricated hollow pier case is floated out to the site, sunk on the piles, and then filled with concrete to form the pier. 如在水下把它们做成桩帽，可把一个预制空心桥墩浮运到场地内并沉入到桩上，然后灌入混泥土形成桥墩。,Erecting the superstructure.建造上部结构 After all piers and abutments are in place, the erection of the superstructure begins 当所有的桩和支柱建好后，则上部结构开始建造。 The method of construction used depends largely on the type of bridge being built. There are six construction methods: falsework , flotation , cantilevering，sliding ,direct lifting, and Suspension. 结构的施工方法有很多种类，共有六类施工方法：脚手架、浮运、悬臂、滑移、直升和悬挂法。,In falswork construction, mainly used in building concrete arch bridges, metal or wood supports are built temporarily to support the erection. 在用脚手架施工时，主要用来建混泥土拱桥，金属或木支撑都是临时搭设为支撑上部结构。 A great deal of ingenuity is often required just to erect the falsework, especially for structures over swift rivers or deep canyons. Temporary piles and trestles are commonly used in wide shallow rivers. Trestle 脚手架, 高架桥, 三角凳 脚手架都是根据需要而灵活搭建的，尤其结构在激流河流或深谷上时，临时桥墩和架子一般在宽而浅的河上使用。,In the floatation method, mainly used in building long bridges , large bridge section are prefabricated on shore and floated out on barges to the bridge site . 浮运法主要用来施工很长的桥梁，主桥部分是在河岸预制的，然后用驳船浮移到桥梁位置。 The sections are then hoisted into place, either by floating derricks or by winches placed on previously constructed sections of the bridge. 浮吊起重机或卷扬机安装在已建成桥的部位，然后把预知的主桥部分精确吊到大桥的施工部位。,The cantilevering technique is used not only for cantilever bridges but also for steel arch bridges. 悬臂技术不仅用于悬臂桥中，也用于刚拱桥上， Construction starts at an abutment and extends toward the center piece by piece. Moving derricks and cranes on the completed portion of the structure handle the heavy material. 施工时先建成一个桥台，然后一步步延伸到中央，在已建好的结构部分的起重机和吊车，来回移动完成施工材料的运输。,Sliding construction is used only rarely. In this method, a prefabricated unit, such as a truss, is erected on shore and slid out over a temporary or permanent support until it comes to rest on another Support. 滑移法在施工中很少用到。这种方法，如一个预制构件，如桁架结构，竖立在河岸上，然后在临时或永久性的支撑滑动，直到它进入安装的另一个支撑上。 In the direct lifting method , mainly used for l