Lesson_7 - Bridge

1、Lesson 7 Bridge桥梁桥梁New words and phrases1、valley vl n. 山谷；流域；溪谷山谷；流域；溪谷 river valley mountain valley the Yangtze valley happy valley2、obstacle bstk()l n. 障碍；障碍物障碍；障碍物 obstacle detection obstacle to + n. 对对的障碍的障碍 an obstacle to progress psychological obstacle3、aqueduct kwdkt n. (1)导水管；水道；水渠；沟渠导水管；水道；

2、水渠；沟渠 (2)（建筑工程）渡槽；高架渠（建筑工程）渡槽；高架渠 aqueous adj. 水的，含水的水的，含水的 duct（Lesson 3）管道）管道 closed aqueduct elevated aqueduct4、pedestrian pdestrn adj. (1)步行的，徒步的；步行的，徒步的；(2)行人的；行人的；(3)平淡的平淡的 n. 步行者，行人步行者，行人 pedestrian street pedestrian crossing5、barge bd n. (1)（在内河、运河或者港湾航行的）驳船，大型平底船（在内河、运河或者港湾航行的）驳船，大型平底船 (2)大

3、型游艇，画舫大型游艇，画舫 vt. (1)用驳船运载用驳船运载 The coal had been barged down to the river. (2)用手推推搡搡地往前走；闯出用手推推搡搡地往前走；闯出 She barged her way through a crowd. vi. barge in 闯入；干涉闯入；干涉 barge into 闯入；与闯入；与相撞相撞6、isolated asletd adj. 孤立的；分离的；隔离的；单独的孤立的；分离的；隔离的；单独的 isolated system isolated layer isolate vt. 使隔离；使孤立；使脱离使隔离

4、；使孤立；使脱离7、 log lg n. 原木；记录；航海日志原木；记录；航海日志 vt. (1)把（树木）锯成段木；切割（树木）成原木把（树木）锯成段木；切割（树木）成原木 He logged the timber into 3 foot lengths. (2)（计算机）把（计算机）把输入计算机输入计算机 log in 注册注册 vi. 伐树，伐木伐树，伐木8、vine van n. 葡萄树；藤本植物葡萄树；藤本植物 grape 葡萄葡萄 wine 酒；葡萄酒酒；葡萄酒9、slant slnt vi. (1)倾斜，歪斜倾斜，歪斜 to slant/sway to the west (2)斜

5、射；斜穿斜射；斜穿 The sunlight slanted through the windows into the room. (3)有倾向性，偏向有倾向性，偏向 to slant toward the majority vt. 使倾斜，使歪斜；斜穿过；倾向于使倾斜，使歪斜；斜穿过；倾向于 n. 倾斜；斜面倾斜；斜面10、swift swft n. （鸟类）雨燕（鸟类）雨燕 adj. 迅速的；立刻的；敏捷的迅速的；立刻的；敏捷的 swift growth swift current adv. 快，迅速地；敏捷地快，迅速地；敏捷地11、subsoil sbsl n. 底土；下层土；天然地基底

6、土；下层土；天然地基 vt. 崛起崛起的底土；深挖的底土；深挖12、gap gp n. 间隙；缺口；空白间隙；缺口；空白 vi. 裂开裂开 vt. 使成缺口使成缺口 generation gap income gap13、aerialist erlst n. 高空杂技师高空杂技师 aerial (Lesson 1) adj. 空气的，大气的空气的，大气的14、tightrope tatrp n. 拉紧的绳索；钢丝拉紧的绳索；钢丝 tight adj. 紧的，绷紧的紧的，绷紧的 rope n. 绳子绳子15、cable keb()l n. 电缆；海底电报电缆；海底电报 v. 打电报打电报16 、

7、abutment btm()nt n. 邻接；接界；（建筑业）拱座，桥墩邻接；接界；（建筑业）拱座，桥墩 bridge abutment 桥台；桥肩桥台；桥肩17、anchorage k()rd n. 锚地；锚定；锚具锚地；锚定；锚具 anchorage force anchor v. 锚定；固定锚定；固定18、stretch stret vt. (1)伸开，展开伸开，展开 (2)使延伸；使延续使延伸；使延续 to stretch the road to the foot of the hill vi. (1)伸展伸展 与与out连用连用 She stretches out in the su

8、n. (2)伸展，延伸伸展，延伸 The forest stretches for miles. n. 伸展伸展 19、girder gd n. 梁，主梁梁，主梁 girder structure 梁式结构梁式结构20 、overlap vlp n. 重叠；重复重叠；重复 v. 与与重叠，交搭重叠，交搭 lap n. 重叠重叠over- (1)太，过于太，过于 overload overconfident (2)完全地完全地 overjoyed (3)上面，外面，额外上面，外面，额外 overcoat overtime (4)上方，上空上方，上空 overhang 21、intersect n

9、tsekt vt. 横穿；贯穿；和横穿；贯穿；和相交；和相交；和交叉交叉 The line AB intersects the line CD at E. vi. 相交；交叉相交；交叉 Streets usually intersects at right angles. 22、corbel arch23 、intermediate pier Text Bridge is a structure that spans obstacles, such as rivers and valleys, to provide a roadway for traffic. By far the major

10、ity of bridges are designed to carry automobile or railroad traffic, but some are intended for pedestrians only.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 carr

11、y taxying aircraft over a highway. The first bridges built by man probably resembled those still being constructed by primitive peoples in isolated regions The tools and building skills of early man, like those of primitive peoples today, were so elementary that he was undoubtedly forced to use easi

12、ly transportable materials that could be put in place with a minimum of forming and shaping. In forest regions, where stout timbers or logs could be obtained, bridges very likely were made of one or more parallel logs, possibly covered with cross branches or matting for better footing. In tropical r

13、egions 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 used to tread on.Other vines, strung several feet higher, were used for hand holds.Although

14、 vine bridges are usually unstable, some built by the Incas were strong and stable enough to be used by the invading Spanish soldiers and their horses. 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

15、path from 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. The first innovation beyond the primitive bridge forms is bel

16、ieved to have occurred in ancient China and then spread to India. To bridge streams wider than a single tree length, the Chinese and Indians used two piles of tree trunks, building toward the stream center from each bank.In each arm of the structure, the logs were piled on top of one another with a

17、slight upward slant, with each layer projected several feet beyond the one immediately below it. For stability, each pile of 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 single beam between the two e

18、nds.In this kind of structure, a crude cantilever bridge, the achievable span length is made greater by the addition of a central section between the free ends of arms. As early as 4000 B.C. in Mesopotamia and 3400 B.C. in Egypt, overlapping horizontal layers of stone or sun-baked brick were used in

19、stead of overlapping timbers. This construction, which looks like a masonry arch that is stepped rather than smooth on the underside is called a corbeled arch.To change the corbeled arch into a true arch, it was only necessary to reorient the inner stones so that they formed a smooth curve.The true

20、arch, which was used as early as 3500 B.C., is much stronger than the corbelled arch. The true masonry arch was efficient, economical, and durable. It could span small rivers by multiple arches resting on piers; moreover, it was generally gracious in appearance.These qualities were hard to match by

21、any previous form of construction.The true masonry arch was widely used in bridge construction by both the ancient Chinese and the Romans; it remained in wide use until the 19th century. Basically there are just four types of structures that can be used to bridge a stream or other obstacle: rigid be

22、ams, cantilevers, arches, and suspension systems. The simplest wayand probably the first usedis to lay a rigid beam across the stream so that its two ends rest on opposite banks.The rigid beam in this type of bridge may be a shaped wooden beam, a girder of steel or concrete, or even a complex truss.

23、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.The materials used for rigid beams must be able to withstand both compression and tension.Rigid BeamThe double requirement stems from the fact that when

24、a load is placed on a rigid beam, the beam bendsin spite of its name.As a result of bending the upper part of the beam is compressed and the lower half is stretched.If its compressive strength is too low, it will buckle；if its tensile strength is too low, it will break.Rigid Beam Often it is not fea

25、sible to construct long span bridges by means of intermediate piers.In deep swift-running rivers or in soft subsoils, for example, it may be difficult to construct the piers or to make them deep enough to reach a firm foundation rock. In such cases the span of a rigid-beam structure can be extended

26、simply by using two beamsone extending from each bankwith one end of each beam firmly anchored to its foundation, rather than simply resting on it as in ordinary rigid-beam construction.CantileverEach of the anchored beams in this kind of structure is called a cantilever.Perhaps the simplest familia

27、r example of a single cantilever is the familiar diving board. 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 cantilever would support itself.Usually

28、the gap between the cantilevers is closed by means of a rigid beam, thus extending the span of the cantilevers.Cantilever Suspension bridges can span even greater distances without intermediate piers than cantilever bridges.The supporting members of a suspension bridge are continuous flexible cables

29、, with each cable anchored at both of its ends.The simplest example of the suspension bridge is the circus aerialists tightrope, and primitive suspension bridges were often no more than several such tightropes tied together to provide both hand and foot holds.In modern suspension bridges a level roa

30、dway is provided by stringing the cables overhead on high towers and suspending the separate roadway below. Suspension 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.Becau

31、se of this difference in shape, the suspension cable tends to pull its anchorages together, while the arch tends to push its abutments apart.For this reason suspension cables must be able to withstand stretching, while arches must be made of materials that can withstand compression.ArchBecause 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.Such materials are useless for