Unit 1: THE HISTORY OF BRIDGE BUILDING
1. What is a bridge? How can you describe it?
2. What obstacles are usual to cross?
3. How long can bridges be?
Find the following terms and memorize their meaning.
Text 1: Bridge
Bridgeis a structure used by people and vehicles to cross areas that are obstacles to travel. Engineers build bridges over lakes, rivers, canyons, and busy highways and railroad tracks. Without bridges, people would need boats to cross waterways and would have to travel around such obstacles as canyons and ravines.
Bridges range in length from a few feet or meters to several miles or kilometers. A bridge must be strong enough to support its own weight as well as the weight of the people and vehicles that use it. It also must resist natural occurrences, including earthquakes, strong winds, and changes in temperature. Most modern bridges have a concrete, steel, or wood framework and an asphalt or concrete roadway. The roadway is the part of a bridge on which people and vehicles travel.
Most bridges are held up by at least two supports set in the ground. The distance between two adjacent supports is called a span of a bridge. The supports at each end of the bridge are called abutments, and the supports that stand between the abutments are called piers. The total length of the bridge is the distance between the abutments. Most short bridges are supported only by abutments and are known as single-span bridges. Bridges that have one or more piers in addition to the abutments are called multi-span bridges. Most long bridges are multi-span bridges. The main span is the longest span of a multi-span bridge.
The prototypical bridge is quite simple—two supports holding up a beam—yet the engineering problems that must be overcome even in this simple form are inherent in every bridge: the supports must be strong enough to hold the structure up, and the span between supports must be strong enough to carry the loads. Spans are generally made as short as possible; long spans are justified where good foundations are limited—for example, over estuaries with deep water. A pontoon bridge has no piers or abutments. It is supported by pontoons (flat-bottomed boats) or other portable floats.
Some special types of bridges are defined according to their function. An overpass allows one transportation route, such as a highway or railroad line, to cross over another without traffic interference between the two routes. The overpass elevates one route to provide clearance to traffic on the lower level. An aqueduct transports water. Aqueducts have historically been used to supply drinking water to densely populated areas. A viaduct carries a railroad or highway over a land obstruction, such as a valley.
All major bridges are built with the public's money. Therefore, bridge design that best serves the public interest has a threefold goal: to be as efficient, as economical, and as elegant as is safely possible. Efficiency is a scientific principle that puts a value on reducing materials while increasing performance. Economy is a social principle that puts value on reducing the costs of construction and maintenance while retaining efficiency. Finally, elegance is a symbolic or visual principle that puts value on the personal expression of the designer without compromising performance or economy. There is little disagreement over what constitutes efficiency and economy, but the definition of elegance has always been controversial.
Modern designers have written about elegance or aesthetics since the early 19th century, beginning with the Scottish engineer Thomas Telford. Bridges ultimately belong to the general public, which is the final arbiter of this issue, but in general there are three positions taken by professionals.
The first principle holds that the structure of a bridge is the province of the engineer and that beauty is achieved only by architecture.
The second idea insists that bridges making the most efficient possible use of materials are by definition beautiful.
The third case holds that architecture is not needed but that engineers must think about how to make the structure beautiful. This last principle recognizes the fact that engineers have many possible choices of roughly equal efficiency and economy and can therefore express their own aesthetic ideas without adding significantly to materials or cost.
I. Decide whether the following statements are true or false according to the text:
1. Bridgeis a structure used by people and vehicles to facilitate traveling.
2. To build a long bridge is very difficult and expensive, so a majority of bridges nowadays don’t range in length more than some hundred meters.
3. Single-span bridges are supported only by two abutments.
4. The main span in the multi-span bridge is the shortest one carrying the main load.
5. Aqueducts were used to provide people with drinking water.
6. Efficiency of a bridge is a scientific principle that takes into account the quantity of people and vehicles passing along the bridge.
7. The definition of elegance is not disputable.
II. Answer the questions:
1. What is a purpose of a bridge?
2. What is the difference between abutments and piers?
3. Why are spans made as short as possible?
4. What types of bridges according to their function can you name?
5. What do you know about a threefold goal of bridge design?
6. Describe three positions in bridge building taken by professionals.
III.What definition of a bridge is correct?
1. a way with a prepared surface, for vehicles, pedestrians, etc.
2. place for crossing a street, water etc.
3. a structure providing a way across a river, road, railway, etc.
4. underground passage dug through a hill or under a road, river, etc.
IV. Make the collocations with the word bridge using the words in ovals and put them into the sentences below. With the rest not used make your own sentences:
1. Bridge is a structure to …
2. A part of a bridge intended to vehicles and pedestrians is called…
3. We can describe … as an each part of a bridge between supports (that are also called as …)
4. According to the quantity of abutments and piers bridges can be … and …
5. A bridge without any abutments or piers is called …
6. A threefold goal to be taken into account while building a bridge is …
7. The road goes … the old railway bridge.
8. The new bridge will … the Thames at this point.
9. Can you see that pontoon bridge … the river?
10. Three positions taken by professionals in bridge building are …
11. The types of the bridge are …, …, … .
12. … means reducing the costs of construction and maintenance.
13. … is putting a value on reducing materials
V. Make the following sentences shorter replacing a set of words with one:
Bridges have always been used by people. They have to be strong and long enough. They also must withstand the action or effect of natural occurrences. Most bridges are held up by supports at each end of the bridge set in the ground. Some bridges have also the supports that stand between the abutments. We can say that there are bridges supported only by abutments (most short bridges) and bridges having one or more piers in addition to the abutments (the longest span of such bridges can be quite long). There is also a bridge with no piers or abutments. While building a bridge engineers discuss the principle that puts a value on reducing materials and the principle that puts value on reducing the costs of construction and maintenance. The principle that puts value on the personal expression of the designer is indisputable.
VI. Choose the following role and make a small report covering the problem mentioned:
· you are a chief engineer and you have to discuss with your team a goal of building a bridge
· you are a modern designer who insists on the principle that beauty is achieved only by architecture, you should promote your ideas to public
· you are a modern designer who insists on the principle bridges making the most efficient use of materials are by definition beautiful
· you are an engineer who thinks that architecture is not needed but that engineers must think about how to make the structure beautiful
· you are a university teacher and you have to make an introduction into speciality of bridge building (you may use the blackboard or cards if necessary)
VII. Write key words of the text so that you can give the main information about bridges.
Последнее изменение этой страницы: 2016-03-16; Просмотров: 142;