大学毕业英文翻译原文.doc

外文翻译原文Bridge Design Concept1 Necessity of bridgesBridges are vitle for the development of a country since these enable transporting materials from one to the other which may be separated by streams and rivers, thereby maintaining uniform flow of essential goods for development. In times of war, materials are swiftly transported for the defence of the country by rail road bridges. Bridges link the whole country with road and railway communication maintaining a uniform flow of people, goods and other essential commodities. The necessity of bridges may therefore be summarized a follows:（1）Bridges enable the free flow of traffic during monsoons and other periods of inclement weather.（2）Bridges provide addition communication facilities.（3）The development of the backward districts which may be rich agriculturally critically depends on the existence of bridges.（4）Bridges provide more socio-economic benefits to the people.（5）Bridges also enable movement of troops and military vehicles during hostilities.2 Site investigation Before a bridge is constructed, a suitable site is selected based on certain factors which have bearing on the economy and stability of the bridge .Reconnaissance is therefore made and the following data are recorded to determine the feasibility of bridge construction. The factors to be considered while selecting the site for a bridge are the following:（1）The bridge should cross the river at right angles to the direction of flow of stream or river water so as to minimize the length of the bridge.（2）The banks on either sides of the river should have firm soil and be straight and well-defined. This will increase the stability of the bridge and reduce the possibility of the erosion of the banks. Also, the soil need not be stabilized or given any other treatment which will increase the cost.（3）The selected site should be at a place where the river is narrow and the flow is a streamlined one without serious whirls and cross currents. Small width reduces the length of the bridge which means less cost of construction and maintenance. If the flow of water is uniform and parallel, it is a reliable guard against scour.（4）Precautions should be taken to see that the selected site should be far away from where the river is likely to change the course. If the bridge has been constructed and the river has changed its course, the bridge will be rendered useless.（5）Hard inerodable strata or rock should be available close to the river bed level.（6）There should not be any sharp curves in road approaches.3 Preliminary data to be collectedThe engineer in-charge of the investigation for a bridge should collect the following information before the construction of a bridge is undertaken：（1）Volume and Nature of Traffic Not only the present volume and nature of traffic but also the future volume which is expected in the next ten years should be collected. The size and the type of the bridge required depend on this data.（2）Velocity of the Stream and High Flood Level (HFL) Attained The discharge of water passing the bridge depends on the velocity of water. It will help in designing the proper size of the waterway and pier thickness. The velocity of the stream during high flood and also during normal flow can be determined with the help of the current meter or velocity rods. The High Flood Level (HFL) will enable a bridge engineer to deter mine the height of free board which is the height of the road way above the HFL. It is necessary to prevent the washing away of the bridge during heavy floods.（3）Catchment Area It is an area of that portion of watershed from which water flows and feeds the river. This is necessary to calculate the discharge of the stream.（4）Strength and Nature of Soil and Extent and Type of Vegetation The depth of foundation for the piers and abutments depends on the strength of soil. This is determined by carrying out borings at several places and testing the soil samples. Extent and type of vegetation along with climatic conditions are also noted.（5）Frequency of Flood Occurrence and Rainfall Details The determination of flood freduency is an important factor as most of the bridges are designed for a flood freduency of 50 years. Amount of rainfall and the HFL are also noted for future design.（6）Scour Depth Determination Eroding of the bed of river due to heavy discharge and the velocity of water known as scour has a great bearing on the design of the depth of foundation of piers and abutments. Hence, the extent to which the bed of the river may scour below the HFL is determined according to which the design is made.4 Technical terms （1）Span：It is the center to center distance between two supports.（2）Culvert：It is a small bridge having maximum span of 6 m.（3）High Flood Level (HFL)：It is the level of the highest flood ever recorded in a river or stream.（4）Ordinary Flood Level (OFL)：It is the level flood level which generally occurs every year.（5）Low water Level (LwL)：It is the minimum water level in the dry weather（6）Waterway：The area of opening which a11ows maximum flood discharge to pass under the bridge without increasing the velocity to a dangerous limit is called waterway.（7）Afflux：Due to construction of the bridge, there is a contraction in waterway. This results in rise of water level above its normal level while passing under the bridge. This rise is known as afflux.（8）Free board：The difference between the H.F.L. and the level of the crown of the road at its lowest point is called free board.（9）Head room：It is the vertical distance between the highest point of a vehicte or vessel and the lowest point of any protruding member of a bridge.（10）Length of the bridge：The length of a bridge structure will be taken as the overall 1ength measured along the center line of the bridge from the end to the bridge deck.（11）Viaduct：It is a continuous structure which carries a road or railway like a bridge over a dry valley composed of series of spans over trestled bents instead of so1id piers.（12）Causeway：It is a submersible bridge which allows floods to pass over it. It is provided on less important routes in order to reduce the construction cost of cross-drainage structures. It may have vents for low water flow.5 Classification of bridges5.1 According to the Expected Uti1ity of Service The bridges are classified as temporary and permanent bridges. （1）Temporary Bridges：The bridges which are constructed and maintained at low cost and have short span of life are called temporary low cost bridges, e.g. Timber bridges.（2）Permanent Bridges：These are bridges which are constructed and maintained at high cost and have a long span of life. These bridges are built to last for centuries, e.g. steel bridges and R.C. bridges.5.2 According to the Position of the F1oor of the BridgeRelative to formation level and highest flood discharge the bridges are classified as deck bridges, through bridges and semi-through bridges. （1）Deck Bridges When the platform of a bridge, carrying the communication route is supported at the top of the superstructure, i.e. when the superstructure of a bridge is accommodated between the high f1ood level and the formation level then the bridges is known as the Deck bridge. （2）Through Bridge when the platform of a bridge，carrying the communication route is suspended at the bottom of the superstructure, i.e. when the superstructure of a bridge projects completely above the formation level then the bridge is known as through type bridge. （3）Semi-through Bridge When the superstructure of a bridge projects partly above and partly below the formation level, it is known as semi-through bridge or pony bridge and is thus an intermediate type between deck and through types.5.3 According to Materials of bridges（1）Timber bridge（2）Masonry bridge（3）Steel bridge（4）RCbridge（5）Prestressed concrete bridge5.4 Movable BridgesMovable bridges are constructed in order to provide headway or opening for navigation ships. The design of bridge superstructure is done in such a way that it can be moved so as to a11ow necessary width and clearance for the passing of ships.Fo11owing are the common types of movable bridges: vertical lift bridge, bascule bridge, and swing bridge.5.5 Culverts A culvert is a drain or water course totally enclosed and usua1ly carried under a road or railway track，the span of which is less then 6m.The common types of culverts are box culvert，pipe culvert and arch culvert. A box culvert consists of one or more square or rectangular openings made of R.C. or masonry but R.C. box culverts are used widely. Box culverts are used for spans less than 4m. A R.C. box culvert is a cheaper a1ternative for a pipe culvert. The abutment op and bottom slabs are a11 cast mono1ithical1y. Pipe culverts are most economical for small drainage crossings. These culverts are generally constructed for diameters less than l.8m.The pipes may be of cast iron or R.C.C. If the soil is of low bearing capacity，the pipes should be bedded in a layer of concrete. If the discharge of water is more than one pipe can be used. Arch culverts are constructed on brick or stone masonry or concrete walls for short spans of 2-3m.Depending upon the loading, span and type of construction, the thickness of an arch may be of 20-50cm. Above the crown of an arch, an earth cushion of at 1east 45cm should be provided.6 The Computer as design Medium A process that cannot be processed. Design is an intensely personal activity. At one extreme there are those who believe that it is cente- red on skilled intuition and that 1ooking too closely at the process is dangerous:1f we try to understand what is going on, perhaps the creative muse will fly away. This “designer as magician” theory, sometimes known as the black-box school, implies that design cannot be taught or externalized. Students have to acquire the skill through a mixture of God-given talent and osmosis from recognized masters. Since we can not define the process，we certainly cannot put it into a computer. In contrast, the glass-box school looks at design as a teachable discipline with recognized methods and procedures that can improve performance. Among the many models of design that have been put forward by researchers, most agree that it invo1ves three identifiable processes of analyzing the problem, synthesizing a solution，and evaluating the result against preconceived aims. Most also agree that this sequence is not linear, but cyclical, so that the result of the evaluation 1eads to a reassessment of the problem(analysis) and a return to the synthesis of a new solution, gradually working from the general scheme to the detailed specification. Indeed design in architecture can be a horribly complicated procedure. Architects are solution-oriented designers. They will jump to a solution as soon as possible, even before analysis has properly begun, as a way of clarifying the problem. They attempt synthesis at a very early stage and are prepared to resynthesize at a very late stage：many an architect has had the embarrassment of explaining to his client why his scheme proposals have drastically changed since their last meeting, when a11 was apparently Fixed. Nor do architects follow an ordered pattern from design concept to detail, often finding themselves thinking of window details before deciding where those windows should be.Nigel Cross quotes studies which suggest that w