1. Find the equivalents:

world obstacles; sea currents; boundary dimensions; seabed silt; maintenance costs; bridge supports; weather conditions; railway tunnel; travel time

10. Choose the best variant:

1. There always was a choice between bridging and tunneling in … over or under a large waterway.

a) crossing b) crippling c) cruising

48. Bridges require lower maintenance … than tunnels.

a) corrosion b) corrugations c) costs

49. Tunnels are much … as compared to the bridge crossing.

a) saving b) saver c) safer

50. Weather conditions cannot influence the … through tunnels.

a) traffic b) transfer c) transit

51. The cost of the tunnel under the English … is enormous.

a) cheddar b) channel c) canal

11. Find the opposites to the words:

gathering _____________

slow _________________

drawback_____________

allow_________________

bound (adj.) ___________

lessening _____________

small_________________

shallow ______________

12. Are the sentences True or False? Correct the wrong ones:

1. ______ The Straits of Gibraltar separates Europe from Africa.

52. ______ The under clearance of the bridges must be over 60 m high not to prevent shipping.

53. ______ For the first time the Bosporus was bridged in 1973.

54. ______ Tunnels require lower maintenance costs.

55. ______ Vessels can navigate much easier if there are no bridges.

56. ______ The Bosporus bridge managed to withstand the wind blows up to 162 km per hour.

13. Make up the word combinations using the derivatives from the words in brackets:

(strong) of the material, bridge (construct), (suspend) bridges, (available) of steel, to be (embed) into the banks, (addition) support, ropes (suspend) from rocks, elaborate (scaffold), period of railroad (expand), to cost (consider), one of the most (common) used, concrete (reinforce) with steel bars.

UNIT 4. REINFORCED CONCRETE AND BEAM BRIDGES.

Vocabulary

Reinforced concrete – железобетон

Possess – обладать

Substitute – заменить

Ribbed – ребристый

Work in compression – работать на сжатие

Reinforcement – арматура

Competitive – конкурентоспособный

Beforehand – заранее

Prestressed – преднапряженный

Jack – домкрат

Bughole – дыра

Beam – балка

Compression – сжатие, компрессия

Tension – напряжение, натяжение, давление

Twisting – закручивание, скручивание

Bending – изгибание, кривизна

Tensile – прочность растяжения при изгибе

To span – соединять, протягиваться,

Dissipate – распределять, уменьшать

Piling – отсыпка, грунт

Daisy chaining – последовательное соединение, гирляндная цепь

A felled log – срубленное бревно

Opposing – противоположные

Concrete being an artificial stone possesses the same good qualities as natural stones. It works well in compression and bad in tension. That is why concrete has substituted natural stone in arch bridges because an arch works in compression.

At the beginning of the 19-th century concrete was reinforced by metal bars. The idea was to transfer the tension stress from the concrete to the reinforcement. This resulted in a new building material, which is known as reinforced concrete.

At present reinforced concrete bridges are widely spread because this building material is in line with short and medium spans (up to 40 – 60-m). It is also rather competitive with metal for long span structures.

The reinforced concrete spans are of a great variety because of their ability to work in compression and tension as well as flexure. It is used for producing simple beams, continuous beams, cantilever-beam systems, arches, frames and combined systems (arch + beam or arch + truss), etc.

The builders use monolithic reinforced concrete laid in situ, prefabricated reinforced concrete, which is made at the works beforehand and the bridge is assembled in-situ from the reinforced concrete segments. Prefabricated monolithic concrete is the combination of both mentioned types. To make the reinforced concrete highly strong and stiff it is prestressed by jacks and reinforcement of high strength wire.

In comparison with other building materials the bridges made of reinforced concrete offer the following advantages: a substantial saving of steel, which is scarce to supply; elimination of maintenance cost as compared with metal bridges; greater rigidity as against metal bridges; long useful life (80 – 100 years); the variety of structural forms improving bridge appearance and architecture.

The disadvantages of the reinforced concrete bridges may be the following: great dead weight; great labor-consuming character of the bridge segments producing; hidden bugholes may cause dangerous complications and they are difficult to be reconditioned; difficulties of concrete laying in winter.

A beam bridge, sometimes called a girder bridge, is a rigid structure that consists of one horizontal beam supported at each end, usually by some kind of pillar or pier. In structural terms, it is the simplest type of bridge and is a popular selection because of its inexpensive construction costs. It began as a felled log supported by opposing riverbanks that was used to span a river or other body of water. Today, it is commonly made from reinforced concrete or steel beams for everything from pedestrian bridges to highway overpasses.

This type of bridge works on the principles of compression and tension, that’s why it needs a strong beam to resist twisting and bending under the weight it must support. When a load, for example a group of traveling cars, pushes down on the beam, the weight of the beam pushes down on the piers. The beam's top edge is pushed together as the result of compression, and tension causes the bottom edge to stretch and lengthen. The top reaches maximum compression while the bottom snaps under too much tension.

Many beam bridges for road construction are made from concrete and steel because these materials are strong enough to bear the forces of compression and tension. The distance a beam can span is directly related to its height, because higher beams offer more material to dissipate tension and need reinforcement.

In spite of reinforcements like concrete, steel, and trusses, its length limits this type of bridge, so they rarely span more than 250 feet (76.2 m). However, daisy-chaining bridge sections allow reaching longer distances. One of the world's longest bridges is a continuous span beam bridge. It’s located in Louisiana as a pair of parallel bridges of the Lake Pontchartrain Causeway that measure almost 24 miles (38.5 km) long and are supported by 9,500 concrete pilings.

Answer the questions:

1. Is there any difference between concrete and reinforce concrete?

2. What is the best length for the reinforced concrete spans and why?

3. What structural model is most preferable for the reinforced concrete bridges?

4. What materials are frequently used in beam bridge construction? Why?

5. What the world's longest beam bridges do you know?

EXERCISES: