I. Decide whether the following statements are true or false according to the text:
1. There are four basic forms: the beam, the arch, the truss and the suspension.
2. A beam carries horizontal loads by bending.
3. The bottom of the beam is subjected to vertical tension.
4. If two or more beams are joined rigidly together over supports, the bridge is called a simply supported beam bridge.
5. A single – span truss bridge carries vertical loads by bending.
6. Trusses are popular because they use a great amount of material to carry large loads.
7. The arch bridge requires more material than a beam bridge of the same span as it has the more complicated foundation design.
8. The deck of the suspension bridge must be either heavy or stiff or both.
9. A cantilever bridge is generally made with two spans.
10. The tensile forces in the cables also put the deck into horizontal compression.
II. Answer the following questions:
1. What are basic bridge forms?
2. What loads does a beam carry by bending?
3. What is the bottom of the beam subject to?
4. When is a bridge called a simply supported beam bridge?
5. When does the bridge become continuous?
6. Why are trusses popular?
7. How does the arch bridge carry loads?
8. What parts of the suspension bridge are subject to compression?
9. Where does the central span rest in a cantilever bridge?
LANGUAGE FOCUS
III. Match the meanings of these terms with their definition:
beam, truss, arch, suspension, cantilever
1. A support on which something is suspended.
2. A large projecting bracket or beam that is supported at one end only.
3. A large long piece of timber ready for use in building or any of the main horizontal supports of a building.
4. A framework of beams or other supports usually connected in a series of triangles and used to form a support for a bridge.
5. A curved structure capable of bearing the weight of the material above it.
IV. Match the words with their synonyms:
1. common 5. exert a) base e) hard
2. carry 6. curved b) strain f) rope
3. foundation 7. cable c) bent g) bear
4. rigid d) usual
V. Fill in the correct prepositions:
1) the location …sth 2) the bottom …sth 3) … the same time
4) to depend … sth 5) a small amount …sth
6) to exert … sth 7) to be transferred …sth 4) to rest …sth
VI. Read the sentences and translate the words in brackets:
1. Engineers (проектируют) bridges of great length and strength to cross the widest rivers.
2. Arches often (образуют) the tops of doors, windows and gateways.
3. The Romans used the semicircular (арки) in bridges, aqueducts and large-scale architecture.
4. Large (балки) carrying the ends of other beams perpendicular to them are usually called girders.
5. For weight reduction beams of metal are formed as an I or other shape having a thin vertical web and thicker horizontal flanges where most of the (нагрузка) appears.
VII. Make the precis of the text
Text 2. TYPES OF BRIDGES
Introduction
Bridge designs differ in the way they support loads. These loads include the weight of the bridges themselves, the weight of the material used to build the bridges, and the weight and stresses of the vehicles crossing them. There are basically eight common bridge designs: beam, cantilever, arch, truss, suspension, cable stayed, movable, and floating bridges. The types of bridges vary in total length, the length of their spans, and the weight they can support. Before deciding which kind to build at a particular place, engineers determine the length of the structure and of each span. They also must consider the maximum load the bridge will carry and the materials available to construct the bridge.
Combination bridges may incorporate two or more of the above designs into a bridge. Each design differs in appearance, construction methods and materials used, and overall expense. Some designs are better for long spans. Beam bridges typically span the shortest distances, while suspension and cable-stayed bridges span the greatest distances.
Beam Bridges
Beam bridges represent the simplest of all bridge designs. A beam bridge consists of a rigid horizontal member called a beam that is supported at both ends, either by a natural land structure, such as the banks of a river, or by vertical posts called piers. Beam bridges are the most commonly used bridges in highway construction. Single-piece, rolled-steel beams can support spans of 15 to 30 m (50 to 100 ft). Heavier, reinforced beams and girders are used for longer spans.
Girder Bridges
Girder bridges, which include many highway bridges, are made of beams called girders whose ends simply rest on piers or abutments. These bridges may be used to cross most areas. The span length of girder bridges ranges up to about 1.000 feet (300 meters).
There are two main types of girder bridges. In one type, called a box girder bridge, each girder looks like a long box that lies between the piers or abutments. The top surface of the bridge is the roadway. Box girder bridges are built of steel or concrete. In the other type of girder bridge, the end view of each girder looks like an I or a T. Two or more girders support the roadway. This type of bridge is called a plate girder bridge when made of steel, a reinforced or prestressed concrete girder bridge when made of concrete, and a wood girder bridge when made of wood.
COMPREHENSION CHECK