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1、 Lesson7 Bridge,课程学习指南：1.words learning Pedestrian(行人)ped(pod，词根)-足 pedal(足的，脚的、脚踏)Subsoil(底土)=sub（前缀：下、次）+soilOverlap(重叠，搭接)=over(前缀：=super)+lap(接)Intersect(交叉)=inter(前缀：相互之间的)+sect(段、部分=part),Bridge is a structure that spans obstacles,such as rivers and valleys,to provide a roadway for traffic.By
2、far the majority of bridges are designed to carry automobile or railroad traffic,but some are intended for pedestrians only.pedestrian noun a person walking along a road or in a built-up area步行者，行人adjective lacking inspiration or excitement;dull缺乏想像力的，平淡无奇的，乏味的,为提供交通道路，桥梁是跨越如河流、山谷这样障碍的一种结构形式，到目前为止，大
3、部分桥梁都是公路桥或铁路桥，仅有少部分是人行桥。,A number of aqueduct bridges,mostly erected in Europe in the 19th century,carry canals and their barge traffic;and at least one bridge,at New York Citys Kennedy Airport,serves to carry taxying aircraft over a highway.aqueduct bridge 高架水渠verb(taxis,taxied,taxiing or taxying)(
4、intransitive)(of an aircraft)move slowly along the ground before takeoff or after landing:the plane taxis up to a waiting car.take a taxi as a means of transport:I would taxi home and sleep till eight.大量的高架渠桥于19世纪在欧洲建成，以保证运河和船舶交通的运行。最小的一座桥在纽约市的肯尼迪机场，它主要是把滑行飞机拖到跑道上服务的。,The first bridges built by man
5、probably resembled those still being constructed by primitive peoples in isolated regions.primitive adj.原始的,早期的简单的;粗糙的原始人,原始事物人类建成的首批桥类似于原始人在孤立地带建成的桥。The tools and building skills of early man,like those of primitive peoples today,were so elementary that he was undoubtedly forced to use easily trans
6、portable materials that could be put in place with a minimum of forming and shaping.早期人类的工具和建筑技术如同原始人类一样都是最初级的，只有应用经过简单加工成型的材料。,In forest regions,where stout timbers or logs could be obtained,bridges very likely were made of one more parallel logs,possibly covered with cross branches or matting for
7、better footing.stout结实的；厚实的 在森林里，随处可得结实的木材，那时侯的桥极可能是由并排的几根圆木建成，可能在其上覆一些木枝或草垫以方便行走。,In tropical regions of India,Africa,and South America,fibrous vines were used to build suspension bridges.The vines were tied to trees or rocks on each side of the stream or valley to be crossed.One or more vines were
8、 used to tread on.Other vines,strung several feet higher,were used for hand holds.stream valley 河谷 处于热带地区的印度、非洲、和南美洲，纤维藤用来建成悬索桥，这些藤系在小河或山谷两边的树上或岩石上，一根或更多的藤用于在上面行走，其它的在几英尺高的地方，用作扶手用。Although vine ridges are usually unstable,some built by the Incas were strong and stable enough to be used by the invad
9、ing Spanish soldiers and horses.invade侵入;侵略(别国);侵犯(主权等)拥入;挤满The town was invaded by a crowd of tourists.虽然藤索桥通常不稳定，但印加人建成的藤索桥足够的坚固和稳定性，被用于西班牙士兵和他们马匹的通行。,In rocky regions,stone was used for bridges.Piles of stone were placed at short intervals across the river,providing the bridge piers,and then a pa
10、th front bank to bank was made by laying flat stone slabs across adjacent piers.A few stone bridges of this type,called clapper bridges,can still be seen in Dartmoor,England;however,they date only from the Middle Ages or even later.在岩石地区，石头被用来建桥，横跨河流以很小的间距布置石碓作为桥墩，然后用平坦的石头跨过相邻的桥墩就建成连接两岸的通道，大部分的石桥就是这
11、种类型，叫做鼓掌桥。现在在Dartmoor、英格兰仍然可见，不过它们都建于中世纪甚至更晚。,The first innovation beyond the primitive bridge forms is believed to have occurred in ancient China and then spread to India.To bridge stream wider than a single tree length,the Chinese and Indians used two piles of three trunks,building toward the stre
12、am center from each bank.pile桩，一堆，一叠 原始桥梁的第一步变革被认为出现在中国古代，随后传入印度。河床一般比树要宽，中国人和印度人从河的两岸到河中央用两堆树干来建造。,In each arm of the structure,the logs were piled on top of one another with a slight upward slant,with each layer projected several feet beyond the one immediately below it.For stability,each pile of
13、timbers was anchored by a massive pile of stone on each bank.Near midstream,the gap between the ends of the arms was closed by the addition of a simple beam between the two ends.每个分支中，圆木一个接一个的布置并微微向上倾斜，使其每一层都比它下面的高几英尺。为了增加稳定性，每个木桩在两岸都用一堆大而重的石头锚固；接近河中央，在河中间的两个分支的两端则用简支梁连接。,In this kind of structure,a
14、 crude cantilever bridge,the achievable span length is made greater by the addition of a central section between the free ends of the arms.crude天然的,未加工的，简陋的,粗糙的,未加修饰，粗鲁的,粗俗的,粗野的在这种结构中，天然支架桥在两个分支的两端加上额外构件后可达到很宽的跨度。,As early as 4000 B.C.in Mesopotamia and 3000 B.C.in Egypt,overlapping horizontal layer
15、s of stone or sun-baked brick were used instead of overlapping timbers.早在公元前4000年的esopotamia和在公元前3000年的埃及，用石头或日光烤干的砖代替木头被用于横向覆盖层。this construction,which looks like a masonry arch that is stepped rather than smooth on the underside is called a corbeled arch这种结构看起来像的砖拱，一层层铺起，被叫做突拱。,T0 change the corbe
16、led arch into a true arch,it was only necessary to reorient the inner stones so that they formed a smooth curve.要使突拱变为真正的拱，需要调整内部石头的构造以形成光滑的曲面。The true arch，which was used as early as 3500 B.C.,is much stronger than the corbeled arch.这种拱比突拱更坚固，且早在公元前500年就被使用。,The true masonry arch was efficient,econ
17、omical,and durable.It could span small rivers by multiple arches resting on piers;moreover,it was generally gracious in appearance.这种石拱经济和经久耐用，它可以由多个跨过桥墩的拱而跨过小的河流，而且外观非常漂亮。These qualities were hard to match by any previous form of construction.The true masonry arch was widely used in bridge construc
18、tion by both the ancient Chinese and the Romans;it remained in wide use until the 19th century.而它的质量比先前的任何结构都要好。在中国和罗马的古代，这种整体石拱被广泛地用于桥梁结构。它一直被广泛地使用直到19世纪。,Basically there are just four types of structures that can be used to bridge a stream or other obstacle:rigid beams,cantilevers,arches,and suspe
19、nsion systems.通常用作河流或障碍物上的桥，有4类基本结构：刚性梁、悬臂、拱、和悬索体系。,Rigid Beam.The simplest way 一 and probably the first used 一 is to lay a rigid beam across the stream so that its two ends rest on opposite banks.刚性梁.最简单也可能是最早使用的刚性梁布置在河流上，两端固定在河的两岸。The rigid beam in this type of bridge may be a shaped wooden beam,a
20、 girder of steel or concrete,or even a complex truss.桥的刚性梁可以是某种形状的木梁、钢筋混凝土梁或复杂的绗架。The span of a rigid beam type of bridge can be increased by building Intermediate piers and bridging the gaps between the piers with several beams.采用在中间建桥墩或用几根横梁连接间隙的方法，可以增加桥刚性梁的跨度。,The materials used for rigid beams m
21、ust be able to withstand both compression and tension.刚性梁的材料必须能够承担压力和拉力，The double requirement stems from the fact that when a load is placed on a rigid beam,the beam bends-in spite of its name.这种双重要求源于梁在荷载作用会产生弯曲。As a result of bending the upper part of the beam is compressed and the lower half is
22、stretched.弯曲的结果，使梁上部受压，下部受拉，If its compressive strength is too low,it will buckle;if its tensile strength is too low,it will break.如果它的受压承载力太弱，它将会屈曲，如果受拉承载力太弱，他将会拉断。,Cantilever.Often it is not feasible to construct long span bridges by means of intermediate piers.In deep swift-running rivers or in s
23、oft subsoil,for example,it may be difficult to construct the piers or to make them deep enough to reach a firm foundation rock.悬臂。利用中间桥墩方式，建造大跨度桥通常是不可行的。举个例子，在深而流速急的河流或软泥中，很难建造墩使它有足够深度达到基岩层。In such cases the span of a rigid-beam structure can be extended simply by using two beams-one extending from
24、each bank with one end of each beam firmly anchored to its foundation,rather than simply resting on it as in ordinary rigid-beam construction.在这种情况下，刚性梁结构用两根梁就可以延伸从每岸伸出一根梁而在两根梁的端部基础进行锚固，这一点与普通刚性梁不同。,Each of the anchored beams in this kind of structure is called a cantilever.Perhaps the simplest fami
25、liar example of a single cantilever is the familiar diving board.每一根锚固的梁称之为悬臂，或许这种最简单而熟悉的悬臂例子便是跳水板。In an ordinary cantilever bridge,the gap between the ends of the cantilevers is closed,providing a continuous deck for the roadway,but if the bridge were cut in two at the point of closure each cantile
26、ver would support itself.在普通的悬臂式桥梁中，悬臂梁端部之间的间隙是闭合的，为道路提供了连续的桥面。但是假如把这种桥梁在其闭合点断开，那么每一根悬臂梁都不需要另外设置支撑而可保持稳定。Usually the gap between the cantilevers is closed by means of a rigid beam,thus extending the span of the cantilevers.通常悬臂梁中间间隙使用刚性梁来闭合，这样，可延伸悬臂梁的跨度。,Suspension.Suspension bridges can span even g
27、reater distances without intermediate piers than can cantilever bridges.悬索。在没有中间桥墩的情况下，悬索桥比悬臂桥跨越更大的距离。The supporting members of a suspension bridge are continuous flexible cables,with each cable anchored at both of its ends.悬索桥的支撑体系是两端锚固的连续可弯曲的缆绳。,The simplest example of the suspension bridge is the
28、 circus aerialists tightrope,and primitive suspension bridges were often no more than several such tightropes tied together to provide both hand and foot holds.悬索桥最简单的例子是杂技场高空走钢丝杂技演员用的钢丝。原始的悬索桥常常是一把很小的几根这样的钢丝系在一起来提供扶手和立足点的。In modern suspension bridges a level roadway is provided by stringing the cab
29、les overhead on high towers and suspending the separate roadway below.在现代悬索桥内，水平道路是由悬吊在高的塔架上缆绳提供，缆绳在车行道的下面。,Arch.The arch is in a sense the opposite of a suspension cable.Where the suspension cable hangs freely from its supporting towers，the arch curves rigidly upward from its abutments.拱则是相反于悬索的作用，
30、在那些悬索的缆绳自由地悬挂在塔架上，拱却是从它的两端拱座处紧紧地向上弯曲。Because of this difference in shape,the suspension cable tends to pull its anchorages together,while the arch tends to push its abutments apart.由于在形状上的不同，悬索使锚固趋向拉在一起，而拱的拱座则趋向于分开。,For this reason suspension cables must be able to withstand stretching,while arches
31、must be made of materials that can withstand compression.由于这些原因，悬索桥的缆绳必须承受一定的延伸作用，而拱材料则尽可能地抵抗压缩作用。Because tensile strength is not necessarily required for arch construction,arch bridges can be made of bricks or stone blocks that are held together by the compressive force characteristic of the arch 因
32、为拱结构不一定要求材料具有抗拉强度，所以拱桥可以用砖或石头建造，砖或石头通过拱传递压力的特性结合在一起。Such materials are useless for the other basic bridge structures.这种材料在其它的基本桥梁结构中却毫无用处。,In an arch bridge,the loads are transmitted vertically down from the roadway until they intersect the arch form.在拱桥中，荷载由公路上垂直传递下来，直到汇集在拱处。At the arch boundary th
33、e loads are redirected along the path of the arch,which is in a state of simple compression.在拱桥中，荷载由公路上垂直传递下来，直到汇集在拱处。在拱的边缘处，荷载便会改变力的传递路径，变为一种简单的受压状态。The compressive thrust forces are then transmitted to the ground through the abutments or piers.The arch,with its simple and elegant structures,has become a classic bridge configuration.有压缩力的推力通过节点或墩传到地面。拱这种简单而优美的结构成为桥梁中的一种基本结构。,
