Lesson_8 - Bridge Design and Construction

1、Lesson 8 Bridge Design and Construction桥梁的设计与建造桥梁的设计与建造New words and phrases1、initiate net vt. (1)开始，着手实施开始，着手实施 to initiate a reform to initiate an attack (2)启发，启蒙；传授（与启发，启蒙；传授（与in/into连用）连用） to initiate sb. into the game of chess (3)介绍介绍加入（与加入（与into连用）连用） to initiate someone into a club n. 新成员；被传授

2、了初步知识的人新成员；被传授了初步知识的人 adj. 新加入的；接受初步知识的新加入的；接受初步知识的 initial nl adj. 开始的，最先的开始的，最先的 initiation ,nen n. 开始；加入开始；加入 initiative ntv n. 主动；主动性主动；主动性2、federal fed()r()l adj. 联邦的；同盟的联邦的；同盟的 federal government/law/court 3、revenue revnju n. 税收，国家的收入；收益税收，国家的收入；收益 tax revenue sales revenue revenue and expendi

3、ture fiscal revenue4、survey sve vt. (1)调查；考察调查；考察 to survey the will of the people (2)测量，勘测测量，勘测 When a project begins, the site is surveyed and mapped by civil engineers. (Lesson 1) (3)俯视，鸟瞰俯视，鸟瞰 to survey Paris from the top of Eiffel Tower vi. 测量，勘测，测绘测量，勘测，测绘 n. 调查；测量；审视调查；测量；审视5、harmony h:mni n.

4、 协调；和睦；和谐协调；和睦；和谐 in harmony live in harmony in harmony with social harmony6、durability ,djrblti n. 耐久性；耐久力耐久性；耐久力 durable djurbl adj. 耐久的；经久的；稳定的耐久的；经久的；稳定的 durability test chemical durability7、accumulation kjumjle()n n. 积累；积聚；聚积物积累；积聚；聚积物 heat accumulation accumulation area8、bump bmp vt. (1)碰，撞，撞击

5、碰，撞，撞击 Her car bumped a truck. (2)使碰撞，冲击使碰撞，冲击 She bumped the car against a post. (3)把把撞到，撞伤（头、臂等）撞到，撞伤（头、臂等） He bumped his arm against the desk. vi. (1)碰，撞（与碰，撞（与against, into 连用）连用） to bump into sb. to bump against the table (2)偶然遇见（与偶然遇见（与 into 连用）连用） I bumped into an old friend in the street. n.

6、 碰撞；撞伤；颠簸碰撞；撞伤；颠簸9、weather we n. 天气；气候；处境天气；气候；处境 vt. (1)使风化；风干，晒干使风化；风干，晒干 They are going to weather the corn in the thrashing field. (2)使退色；使分解；侵蚀使退色；使分解；侵蚀 The wind and waves have weathered the rocks on the shore. (3)渡过（暴风雨，困难等）；经受住渡过（暴风雨，困难等）；经受住 Many small firms did not weather the storm of the

7、 recession. vi. 受侵蚀；风化；经受风雨受侵蚀；风化；经受风雨 n. weather forecast weather permitting10、tremor trem n. 颤动；震动颤动；震动 vi. 发抖；颤动发抖；颤动11、debris debri n. 碎片，残骸碎片，残骸 debris flow12、cofferdam kfdm n. （河流、湖泊等的）围堰；潜水箱，沉箱（河流、湖泊等的）围堰；潜水箱，沉箱 antiseepage cofferdam earth cofferdam13、caisson kes()n n. 沉井，沉箱沉井，沉箱 caisson pile

8、 open caisson14、hazardous hzds adj. 有危险的；冒险的；（化合物）有害的有危险的；冒险的；（化合物）有害的 hazardous waste hazardous goods hazard vt. 冒冒的危险；赌运气的危险；赌运气 n. 危险；冒险危险；冒险15、temporary temp()rr adj. 临时的；暂时的；短暂的临时的；暂时的；短暂的 temporary work temporary construction n. 临时工；临时雇员临时工；临时雇员16、ingenuity ,ndnjut n. 心灵手巧；独创性；精巧；精巧的装置心灵手巧；独创性

9、；精巧；精巧的装置 originality n. 创意；独创性创意；独创性 17、derrick derk n. 起重机；起货桅杆起重机；起货桅杆 v. 用转臂起重机移动或吊起用转臂起重机移动或吊起18、winch wnt vt. 用绞车提升；用起货机吊起用绞车提升；用起货机吊起 n. 绞车；曲柄；卷扬机绞车；曲柄；卷扬机 19、guardrail drel n. 护栏；栏杆；护栏；栏杆；铁路铁路护轨护轨 guard v. 保卫；监视保卫；监视 n. 守卫；防护守卫；防护20、accessory kses()r adj. 附加的；辅助的；附属的；副的附加的；辅助的；附属的；副的 accesso

10、ry equipment accessory ingredient n. 配件；附件；附属品配件；附件；附属品21、toll tl n. 税；（桥梁、公路等的）通行费，通过费税；（桥梁、公路等的）通行费，通过费 v. 征税；收通行费征税；收通行费 road toll toll station22、preliminary design 初步设计初步设计23、tensile strength 抗拉强度抗拉强度 compressive strength 抗压强度抗压强度24 、yield strength 屈服强度屈服强度25、suspension bridge 吊桥，悬索桥吊桥，悬索桥26、com

11、pressed air 压缩空气压缩空气 Text Bridge Design and ConstructionPlanning The first step leading to the construction of a modern major bridge is a comprehensive study to determine whether a bridge is needed. If it is to be a highway bridge, in the United States for example, a planning study is initiated by a

12、 state bridge authority, possibly in cooperation with local government or the federal government .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. The means for financin

13、g the project, such as public taxes or sale of revenue bonds repaid by toll charges, are considered.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. At this point, field engineering work is started. Ac

14、curate land surveys are made.Tides, flood conditions，currents, and other characteristics of the waterway are carefully studied.Boring samples of soil and rock are taken at possible foundation locations, both on land and under the water. The chief factors in deciding whether a bridge will be built as

15、 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.Each type of brid

16、ge is most effective and economical only within a certain range of span lengths, as shown in the following table:Selection of bridge design 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

17、prepared for several types of bridge in order to have a better basis for making the final selection.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.For the Verrazano-Narrows Bridge, for

18、example, the designer used at least seven different kinds of alloy steel, one of which has a yield strength of 50,000 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 corrosionThe designer also can select steel wi

19、res for suspension cables that have tensile strengths up to 250, 000 psi(17, 577 kgsq cm)Selection of materials Concrete with compressive strengths as high as 8, 000 psi (562.5 kgsq cm) can now be produced for use in bridges, and it can be given high durability against chipping and weathering by the

20、 addition of special chemical agents and control of the hardening process.Concrete that has been prestressed and reinforced with steel wires has a tensile strength of 250, 000 psi ( 17, 577 kg / sq cm). Other useful materials for bridges include aluminum alloys and wood.Modern structural aluminum al

21、loy have yield strengths exceeding 40, 000 psi (2, 812 kg / sq cm).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 3, 000 psi (210.9 kg /sq cm). A bridge must

22、 resist a complex combination of tension, compression, bending, shear, and torsion forces.In addition, the structure must provide a safety factor as insurance against failure. The calculation of the precise nature of the individual stresses and strains in the structure, called analysis, is perhaps t

23、he most technically complex aspect of bridge building.The goal of analysis is to determine all of the forces that may act on each structural member.Analysis of forces The forces that act on bridge structural members are produced by two kinds of loads-static and dynamic.The static load - the dead wei

24、ght 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. Although the total weight of the vehicles moving over a bridge at any time is generally a small fract

25、ion 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.For example, the severe impacts caused by irregularities of vehicle motion or bumps in the roadway may momentarily double the effect of the

26、live load on the bridge. Wind exerts force on a bridge both directly by striking the bridge structure and indirectly by striking vehicles that are crossing the bridge.If the wind induces aeroelastic vibration, as in the case of the Tacoma Narrows Bridge, its effect may be greatly amplified.Because o

27、f this danger, the bridge designer makes provisions for the strongest winds that may occur at the bridge location.塔科马海峡大桥塔科马海峡大桥塔科马海峡大桥蛇形共振塔科马海峡大桥蛇形共振1940年年11月月7日塔科马海峡大桥倒塌日塔科马海峡大桥倒塌 Other forces that may act on the bridge, such as stresses created by earthquake tremors, must also be provided for.Spe

28、cial 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 ship. Electronic computers are playing an ever-increasing role in assisting bridge designers

29、 in the analysis of forces.The use of precise model testing, particularly for studying the dynamic behavior of bridges, also helps designers.A scaled-down model of the bridge is constructed, and various gauges to measure strains, accelerations, and deformations are placed on the model. The model bri

30、dge is then subjected to various scaled-down loads or dynamic conditions to find out what will happen.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 pas

31、t. Construction starts with the foundation, which may cost almost as much as the superstructure.Foundations built in water usually present the greatest difficulties.One of the older methods, which is still used in shallow waters, is to erect cofferdams similar to the ring of closely spaced piles tha

32、t the Romans used.Construction the foundations For constructing foundations in deep water, caissons have long been used.The caisson, which is a huge box closed on all sides except the bottom, is lowered onto the river bed.Workers inside the caisson, which is filled with compressed air to keep out th

33、e water, dig deeper and deeper, and the caisson sinks as the digging proceeds.keep out(1)使留在外面；挡住；不让进来使留在外面；挡住；不让进来The little girl has never seen him before and so she keeps the stranger out.(2)留下，扣下留下，扣下The company keeps 5% of his salary out each month.When a suitable depth is reached，the caisson i

34、s filled with concrete and becomes part of the foundation itself . Another deep-water method, less hazardous and less costly than the caisson method, uses steel or concrete piles.With modern pile drivers, long heavy piles can be driven even in deep water.The piles can be cut off and capped either ab

35、ove the water level or below it.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. After all piers and abutments are in place, the erection of the superstructure beginsThe method of

36、 construction used depends largely on the type of bridge being built.There are six construction methods: falsework, flotation, cantilevering, sliding, direct lifting, and suspension.Erecting the superstructure In falsework construction, mainly used in building concrete arch bridges, metal or wood su

37、pports are built temporarily to support the erection.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. In the floatation method, mainly used in bu

38、ilding long bridges , large bridge section are prefabricated on shore and floated out on barges to the bridge site .The sections are then hoisted into place, either by floating derricks or by winches placed on previously constructed sections of the bridge. The cantilevering technique is used not onl

39、y for cantilever bridges but also for steel arch bridges.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. Sliding construction is used only rarely.In this method, a prefabri

40、cated 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. In the direct lifting method, mainly used for light, short - span highway bridge, a prefabricated bridge unit is lifted by a hoist and swung directly onto the bridge supports. In the construction of suspension bridges, the cables are strung between the bridge towers and used as a support for the bridge deck.The deck erection starts at the ends of the bridge and progresses toward the cent