大学毕业英文翻译原文
Bridge Design Concept
1 Necessity of bridges
Bridges 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
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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.
design翻译3 Preliminary data to be collected
The 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.
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（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 o
f 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 fou
ndation 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
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（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.

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