《专业英语》课件Unit-9.pptx

1、TextBridges touch all our livesevery day we are likely to cross or go under a bridge.But how many of us stop to consider how the bridge works and what sort of people designed and built it.There are three practical requirements for a successful bridgefirm foundations,strong structure,and effective wo

2、rking.Firm foundations are especially critical for traditional structures such as arches.Indeed once erected,arches will stay in place for a very long time as long as the foundations dont move.All bridges require strong robust and stable structure.However,the real test for a successful bridge is whe

3、ther it works effectively.Bridges stand up because the basic structural components interact and work effectively with each other.The foundations,strength,and effectiveness of the aesthetic,social,and cultural aspects of bridges are much more difficult to capture but are nonetheless very important.Br

4、idges are icons for whole citiesthink of New Yorks Brooklyn Bridge,Sydneys Harbour Bridge,and Brunels Clifton Bridge in Bristol.With a recorded history of about 5000 years,China has a vast territory,topographically higher in the northwest and lower in the southeast.Networked with rivers,China has th

5、e well-known valleys of the Yangtze River,the Yellow River,and the Pearl River,which are the cradle of the Chinese nation and culture.TextThroughout history,the Chinese nation erected thousands of bridges,which form an important part of Chinese culture.All bridges and other structures,including the

6、human body,have what scientists call a natural frequencywhen objects vibrate freely.Bridges with spans similar to the London Millennium Bridge typically vibrate with natural frequencies between 0.5 and 1.0 cycles per second.If wind or pedestrians apply forces to the bridge at the same frequency as t

7、he natural frequency then resonance occurs and the vibrations can become very large indeed.When we walk across a bridge we push down with each step but we also push outwards slightly as well.The structural engineers did extensive calculations and thought that they had all these possible sources of w

8、obble covered.The list of materials from which bridges are made is actually quite short.It includes timber,masonry,concrete,iron,steel,and more recently aluminium and plastics,but little else.Bridge materials must be strong enough for the job they will be asked to do,readily available,and not too ex

9、pensive.Of course combinations of material are used.For example,because concrete is strong when squashed but weak when pulled,steel bars are used to reinforce it.TextThe grammar of how bridges put together are generally based on combinations of four sub-structural typesBATSbeams,arches,trusses,and s

10、uspensions1.For example,the Golden Gate Bridge is a suspension bridge with a roadway deck on a stiff truss beam.Beam BridgesSimple in structure,convenient to fabricate and erect,easy to maintain,and with less construction time and low cost,beam structures have found wide application in short-to medi

11、um-span bridges.In 1937,over the Qiantang River,in the city of Hangzhou,a railway-highway bipurpose bridge was erected,with a total length of 1453 m,the longest span being 67 m.When completed,it was a remarkable milestone of the beam bridge designed and built by Chinese engineers themselves.Reinforc

12、ed concrete beam structures are most commonly used for short-to medium-span bridges.A representative masterpiece is the Rong River Bridge completed in 1964 in the city of Nanning,the capital of Guangxi Zhuangzu Autonomous Region.The bridge,with a main span of 55 m and a cross section of a thin-walle

13、d box with continuous cells,designed in accordance with closed thin walled member theory,is the first of its kind in China.Prestressed concrete beam bridges are a new type of structure.China began to research and develop their construction in the 1950s.TextThe extensive construction of continuous be

14、am bridges has led to the application of the incremental launching method especially to straight and plane curved bridges2.In addition,large capacity(500 t)floating crane installation and movable slip forms as well as span erection schemes have also attained remarkable advancement.Arch BridgesOf all

15、 types of bridges in China,the arch bridge takes the leading role in variety and magnitude.Statistics from all the sources available show that close to 60%of highway bridges are arch bridges.China is renowned for its mountains with an abundant supply of stone.Stone has been used as the main construc

16、tion material for arch bridges.Most of the arches used in China fall into the following categories:box arch,two-way curved arch,ribbed arch,trussed arch,and rigid framed arch.The majority of these structures are deck bridges with wide clearance,and it costs less to build such bridges.The box arch is

17、 especially suitable for long-span bridges.The longest stone arch ever built in China is the Wu River Bridge in Beiling,Sichuan Province,whose span is as long as 120 m.The Wanxian Yangtze River Bridge in Wanxian,Sichuan Province with a spectacular span of 420 m set a world record in the concrete arc

18、h literature.Text A unique and successful improvement of the reinforced concrete arch,the two-way curved arch structure,which originated in Wuxi,Jiangsu Province,has found wide application all over the country,because of its advantages of saving labor and falsework.T-Type and Continuous Rigid Frame

19、BridgesThe prestressed concrete rigid T-frame bridge was primarily developed and built in China in the 1960s.This kind of structure is most suitable to be erected by balanced cantilever construction process,either by cantilever segmental concreting with suspended formwork or by cantilever erection w

20、ith segments of precast concrete3.The first example of cantilever erection is the Wei River Bridge(completed in 1964)in Wuling,Henan Province,while the Liu River Bridge(completed in 1967)in Liuzhou in Guangxi Zhuangzu Autonomous Region is the first by cantilever casting.The Yangtze River Highway Bri

21、dge at Chongqing(completed in 1980),having a main span of 174 m,is regarded as the largest of this kind at present.From prestressed concrete rigid T-frame bridges were developed multiple prestressed concrete continuous beam and continuous rigid frame bridges,which can have longer spans and offer bet

22、ter traffic conditions.Among others,the Luoxi Bridge in Guangzhou,Guangdong Province(completed in 1988)features a 180-m main span.The Huangshi Yangtze River Bridge in Hubei Province has a main span of 245 m.TextAnd the Humen Continuous Rigid Frame Bridge in Guangdong Province(completed in 1997),whic

23、h has a 270-m main span,is regarded as the largest of this kind in the world.Luoxi bridge,the longest prestressed concrete continuous rigid frame bridge in China,spans Pearl River in Guangzhou,Guangdong Province.It is 1916.04 m long and 15.5 m wide.The main bridge has spans of 65+125+180+110 m,provi

24、ding a navigation clearance of 34 120 m.Steel BridgesSteel structures are employed primarily for railway and railwayhighway bi-purpose bridges.In 1957,in the city of Wuhan,a railwayhighway bi-purpose bridge was erected over the Yangtze River,another milestone in Chinas bridge construction history.Na

25、njing Yangtze River Bridge is a highway and railway double-deck continuous steel truss bridge in Nanjing,Jiangsu Province.On the upper deck there are four lanes of highway traffic,which are 15 m wide,plus two sidewalks of 2.25 m wide each,and on the lower deck two tracks for railway.The main bridge

26、is 1576 m long.If approaches are taken into account,the length of the railway bridge reaches 6772 m and the highway bridge is 4588 m long4.TextCable-Stayed BridgesCable-stayed bridges,like suspension bridges,are held up by cables.However,in a cable-stayed bridge,less cable is required and the towers

27、 holding the cables are proportionately shorter.The first known cable-stayed bridge was designed in 1784 by C.T.Loescher.The longest cable-stayed bridge is the Sutong Bridge over the Yangtze River in China.Fixed or movable bridgesMost bridges are fixed bridges,meaning they have no moving parts and s

28、tay in one place until they fail or are demolished.Temporary bridges,such as Bailey bridges,are designed to be assembled,and taken apart,transported to a different site,and re-used.They are important in military engineering,and are also used to carry traffic while an old bridge is being rebuilt.Mova

29、ble bridges are designed to move out of the way of boats or other kinds of traffic,which would otherwise be too tall to fit.These are generally electrically powered.Suspension BridgesSuspension bridges are suspended from cables.The earliest suspension bridges were made of ropes or vines covered with

30、 pieces of bamboo5.In modern bridges,the cables hang from towers that are attached to caissons or cofferdams.The caissons or cofferdams are implanted deep into the floor of a lake or river.Text The longest suspension bridge in the world is the 12,826 feet(3,909m)Akashi Kaikyo Bridge in Japan.See sim

31、ple suspension bridge,stressed ribbon bridge,underspanned suspension bridge,suspended-deck suspension bridge,and self-anchored suspension bridge.All preventive maintenance projects should consider appropriate ways to maintain or enhance the current level of safety and accessibility.Isolated or obvio

32、us deficiencies should always be addressed.Safety enhancements such as the installation or upgrading of guardrail and end treatments,installation or replacement of traffic signs and pavement markings,removal or shielding of roadside obstacles,mitigation of edge drop offs,the addition of paved or sta

33、bilization of unpaved shoulders,or installation of milled rumble strips should be encouraged and included in projects where they are determined to be a cost effective way to improve safety.Timely preventive maintenance and preservation activities are necessary to ensure proper performance of the tra

34、nsportation infrastructure.Experience has shown that when properly applied,preventive maintenance is a cost-effective way of extending the service life of highway facilities and therefore is eligible for Federal-aid funding.By using lower-cost system preservation methods,the county can improve syste

35、m conditions,minimize road construction impacts on the traveling public,and better manage their resources needed for long-term improvements such as reconstruction or expansion.New Words and Phrasesrobust a.强健的；粗野的；粗鲁的cradle n.摇篮；发源地，发祥地pedestrian n.行人；a.步行的，徒步的wobble v.摇晃；摇摆squash v.受挤压；挤入fabricate

36、v.制作，建筑；装配，组合erect v.使竖立；建造；安装incremental a.增加的；递增的falsework n.脚手架；临时支架precast a.预制的；预浇铸的milestone n.里程碑，划时代的事件military a.军事的；军人的；适于战争的navigation n.航行，航海，航运proportionately adv.相称地，成比例地vine n.藤本植物；攀缘植物implant v.嵌入；埋置，埋藏deficiency n.缺陷，缺点；缺乏guardrail n.护栏；栏杆；铁路护轨mitigation v.减轻；缓和；平静eligible a.合格的，合适的

37、New Words and Phrasesnatural frequency n.固有频率London Millennium Bridge n.伦敦千禧桥Golden Gate Bridge n.金门大桥beam bridge n.梁桥arch bridge n.拱桥continuous rigid frame bridge n.连续刚构桥cable-stayed bridge n.斜拉桥suspension bridge n.悬索桥，吊桥Notes1.The grammar of how bridges put together are generally based on combinat

38、ions of four sub-structural typesBATSbeams,arches,trusses,and suspensions.桥梁成为一个整体的基本原理在于四种亚结构类型(BATS)的组合：梁、拱、桁架和悬架。2.The extensive construction of continuous beam bridges has led to the application of the incremental launching method especially to straight and plane curved bridges.连续梁桥的大型构造导致了顶推法的应

39、用，该方法尤其适用于直线和平面弯桥。3.This kind of structure is most suitable to be erected by balanced cantilever construction process,either by cantilever segmental concreting with suspended formwork or by cantilever erection with segments of precast concrete.此类结构最适合采用平衡悬臂施工工艺竖起，或采用带有悬吊式模板的悬臂分段式浇筑工艺或预制混凝土段悬臂梁架设工艺。4

40、.If approaches are taken into account,the length of the railway bridge reaches 6772 m and the highway bridge is 4588 m long.如果考虑路径，则铁路桥的长度达到 6772 m，公路桥长度为 4588 m。5.The earliest suspension bridges were made of ropes or vines covered with pieces of bamboo.最早的悬索桥是由绳索或树藤覆盖以竹板构成。Exercise（Translate the fo

41、llowing Chinese into English,or English into Chinese）1.因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块建造。2.横跨河流以很小的间距布置石堆作为桥墩，然后用平坦的石头横过相邻的桥墩就建成连接两岸的通道。3.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 m

42、ade 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 b

43、edrock.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.Exercise（Translate the following Chinese into English,or English into Chinese）4.T

44、hree 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.

45、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

46、 factors must be taken into consideration in the design of a bridge.5.Considering the complex geologic conditions at the bridge site,different types of foundations were used:heavy concrete caissons with a depth of penetration reaching 54.87 m for areas with shallow water and deep coverings;a floating-type steel caisson combined with pipe column foundations was used for the first time at sites of deep water.The bridge was designed and constructed by the Major Bridge Engineering Bureau,Ministry of Railways.It was completed in December 1968.