土木专业外语大作业.doc

土木工程专业外语 姓 名：_ 学 号：_班 级：_土木1109_日 期：_2013.12.20_原文：（Unit12)text Bridge Factors Acting on a BridgeBridges are structures that provide a means of crossing natural barriers, such as rivers, lakes, or gorges. Bridges are designed to carry railroad cars, motor vehicles, or pedestrians. Bridges also support pipes, troughs, or other conduits that transport materials, such as an oil pipeline or a water aqueduct.Humans have been constructing bridges since ancient time. The earliest bridges were probably nothing more than felled trees used to cross rivers or ditches. As civilization advanced, artisans discovered ways to use stone, rock, mortar, and other natural materials to construct longer and stronger bridges. Finally, as physicists and engineers began to develop the principles underlying bridge construction, they incorporated other materials such as iron, steel, and aluminum into the bridges they built. There are four major types of bridges: beam, cantilever, arch, and suspension.Three kinds of forces operate on any bridge: the dead load, the live load, and the dynamic load. Dead load refers to the weight of the bridge itself. Like any other structure, a bridge has a tendency to collapse simply because of the gravitational forces acting on the materials of which the bridge is made. Live load refers to traffic that moves across the bridge as well as normal environmental factors such as changes in temperature, precipitation, and winds. Dynamic load refers to environmental factors that go beyond normal weather conditions, factors such as sudden gusts of wind and earthquakes. All three factors must be taken into consideration in the design of a bridge.Words to Know Abutment: Heavy supporting structures usually attached to bedrock and supporting bridge piers.Bedrock: Portion of Earths mantle made of solid rock on which permanent structures can be built.Dead load: The force exerted by a bridge as a result of its own weight.Dynamic load: The force exerted on a bridge as a result of unusual environmental factors, such as earthquakes or strong gusts of wind.Live load: The force exerted on a bridge as a result of the traffic moving across the bridge.Piers: Vertical columns, usually made of reinforced concrete or some other strong material, on which bridge rest.Suspenders: Ropes or steel wires from which the roadway of a bridge is suspended.Truss: A structure that consists of a number of triangles joined to each other.Beam bridges: The simplest type of bridge consists of a single piece of material that stretches from one side of a barrier to the other side. That piece of materialcalled a beam or girderrests directly on the ground on each side or is supported on heavy foundations known as piers. The length of a beam bridge is limited by the weight of the beam itself plus the weight of the traffic it carries. Longer beam bridges can be constructed by joining a number of beams to each other in parallel sections.Cantilever bridges: A cantilever is a variation of the simple beam bridge. A cantilever is a long arm that is anchored at one end and is free to move at the opposite end. A diving board is an example of a cantilever. When anchored firmly, a cantilever is a very strong structure. It consists of three parts: the outer beams, the cantilevers, and the central beam. The on-shore edge of the outer beams is attached to the ground itself or to a pier (usually a vertical column of reinforced concrete) that is suck into the ground. The opposite edge of the outer beam is attached to a second pier, suck into the ground at some distance from the shore. Also attached to the off-shore pier is one end of a cantilever. The free end the cantilever extends outward into the middle of the gap between the shores. The cantilevers on either side of the gap are then joined by the central beam.Caisson: To build bridge piers, workers need a water-free environment to excavate or dig the foundations. This is achieved by using a caisson, a hollow, water-tight structure made of concrete, steel, or other material that can be sunk into the ground. When building a bridge over a river, workers sink a caisson filled with compressed air into the river until it reaches the river bottom. The workers then go into the caisson and dig out soil from the riverbed until they come to bedrock. The caisson, which has sharp bottom edges, continually moves downward during the digging until it comes to rest on bedrock. Concrete is then poured into the caisson to form the lowest section of the new bridge pier.Trusses: The strength of a cantilever bridge (or any bridge) can be increased by the use of trusses. A truss is the structure that consists of a number of triangles joined to each other. The triangle is an important component of many kinds of structures because it is the only geometric figure that cannot be pulled or pushed out of shape without changing the length of one of its sides. The cantilever beam, end beams, and joining beams in a cantilever bridge are often strengthened by adding trusses to them. The trusses act somewhat like an extra panel of iron or steel, adding strength to the bridge with relatively little additional weight. The open structure of a truss also allows the wind to blow through them, preventing additional stress on the bridge from this force.Arch bridges: The main supporting structure in an arch bridge is one or more curved elements. The dead and live forces that act on the arch bridge are transmitted along the curved line of the arch into abutments or supporting structures at either end. These abutments are sunk deep into the ground, into bedrock if at all possible. They are, therefore, essentially immovable and able to withstand very large forces exerted on the bridge itself. This structure is so stable that piers are unnecessary in an arch bridge. The roadway of an arch bridge can be placed anywhere with relationship to the arch: on top of it, beneath it, or somewhere within the arch. The roadway is attached to the arch by vertical post (ribs and columns) if the roadway is above the arch, a bowstring arch bridge in Arizona. The roadway is supported from the arch by suspenders, by ropes or cables (suspenders) if the roadway is below the arch; and by some combination of the two if the roadway is somewhere within the arch.Suspension bridges: In a suspension bridge, thick wire cables run across the top of at least two towers and are anchored to the shorelines within heavy abutments. In some cases, the roadway is supported directly by suspenders from the cable. In other cases, the suspenders are attached to a truss, on top of which the roadway is laid. In either case, the dead and live loads of the bridge are transmitted to the cables which, in turn, exert stress on the abutments. That stress is counteracted by attaching the abutments to bedrock. The towers in a suspension bridge typically rest on massive foundations sunk deep into the riverbed or seabed beneath the bridge itself. The wire cables that carry the weight of the bridge and its traffic are made of parallel strands of steel wire woven together to make a single cable. Such cables typically range in diameter from about 15 inches (38 centimeters) to as much as 36 inches (91 centimeters).Movable bridge: Traditionally, three kinds of movable bridges have been constructed over waterways to allow the passage of boat traffic. In a swing bridge, the roadway rotates around a central span, a large, heavy pier sunk into the river bottom. In a bascule bridge, the roadway is raised like an ancient drawbridge. It can be lifted either at one end or split in two halves in the middle, each half rising in the opposite direction. In a vertical-lift bridge, the whole central portion of the bridge is raised straight up by means steel ropes.译文： 作用在桥梁上因素 桥梁结构是一种提供跨自然障碍的工具，例如河流，湖泊，峡谷。桥梁的设计是用来使铁路车辆，机动车辆或行人通过的。桥梁也支持管道，槽，或其他管道运输的材料，如石油管道或水渠。 人类自古以来一直在建设桥梁。最早的桥梁恐怕只是砍伐一些树木用于穿越河流或沟渠。随着人类文明的进步，工匠们发现一些用石头，砂浆和其他的天然材料来建造跨度更长和强度更强的桥梁的方法。最后，随着物理学家和工程师开始发展桥梁建设的原理基础，他们把其他材料如铁，钢，铝应用用在其它桥梁建造中。有四种主要类型的桥梁：梁桥，悬臂梁，拱，和悬浮。 有三种施加在桥梁上的荷载：恒载，活载，和动态负载。静荷载是指桥自身的重量。像任何其他结构，桥上有一种倾向，崩溃仅仅因为引力作用于用来建造桥梁的材料。活荷载是指在桥梁上行走的交通车辆以及正常的环境因素，如温度的变化，雨水量的改变，风大小的改变。动荷载是指超越正常的天气条件的环境因素，如突发的强风和地震。这三个因素在桥梁设计中都必须要考虑到， 需要知道的专业术语 桥墩：重支撑结构通常固定在岩床和桥墩。 岩床：由岩石组成的可以在上面可以建造建筑物的地表覆盖。 恒荷载：由于桥梁自身的重量而产生的力。 动态载荷：由于不寻常的环境因素，如地震或强阵风风而产生的作用在桥梁上的力。 活荷载：由于在桥梁上穿梭的交通车辆的流动而产生的作用在桥梁上的力。 桥墩：垂直柱，通常由钢筋混凝土或其他一些强有力的材料，桥建在它上边。 吊杆：绳索或钢丝从其中的一个桥巷穿过。 桁架：由很多三角形相互连接的一种结构 梁桥：最简单的一种由单独的一种材料组成从一侧延伸到另一侧的桥。那种被称为桥梁或者桥的材料是直接在地面上的每一侧上或支承在桥墩基础上承载重量的。梁桥的长度是由桥梁自身的重量和它所载的交通重量所限制的。长梁桥可以通过加入一些相互平行的梁区段来建造。 悬臂桥：悬臂是一种变异的简支梁桥。悬臂是一个一端固定，而另一端是自由移动的很长的臂。跳板是悬臂的一个例子。当悬臂梁被固定牢固时，它是一个非常强大的结构。它由三部分组成：外梁，悬臂梁，和中央桥梁。外梁的边缘被连接到地面本身或被固定在地面上的一个码头（通常是一个垂直的柱钢筋混凝土）上。与外梁相对的边缘被连接到离海岸线有一定距离，被固定在地面上的第二个桥墩。同时连接到离岸码头是悬臂的一端。自由端的悬臂向外延伸到海岸之间的空隙。在缝