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Unit 3. Reinforced Concrete Bridges.
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Vocabulary.
reinforced concrete — железо-бетон
possess — обладать
substitute — заменить
ribbed - ребристый
work in compression — работать на сжатие
reinforcement — арматура
competitive — конкурентоспособный
beforehand — заранее
prestressed — преднапряженный
jack—домкрат
bughole — дыра
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.
Sometimes to reduce the structure weight they substitute the most usual coarse aggregate such as crushed rock, pebbles, and gravel by slag and bloating clay. This results in light concrete.
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.
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?
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Exercises:
1) Find the equivalents:
железобетонный мост
заменять, замещать
пред напряженная арматура
заранее
обычная арматура
плитное пролетное строение
ребристое пролетное строение
раскос
жесткий нижний пояс балки
стенка
шпала
отверстия
отогнутый
домкрат
сварочная сталь
2) Choose the right answer:
1. Concrete has substituted natural stone in arch bridges because
A it works well in tension.
B it works well in bending.
C it works well in compression.
D it works well in torsion.
2. Prefabricated monolithic concrete is…
A. usually called monolithic reinforced concrete.
B. the combination of monolithic reinforced concrete and prefabricated reinforced concrete.
C. usually called prefabricated reinforced concrete.
D. the combination of monolithic reinforced concrete and prestressed concrete.
3. The disadvantages of the reinforced concrete bridges are
A a substantial saving of steel; elimination of maintenance cost; greater rigidity.
B the variety of structural forms; difficulties of concrete laying in winter; hidden bugholes.
C hidden bugholes; a substantial saving of steel; elimination of maintenance cost.
D great dead weight; difficulties of concrete laying in winter; hidden bugholes.
3) Divide the words into pairs:
metal
high-strength
bug
concrete
structure
prestressed
laying
wire
bar
concrete
holes
weight
4) Fill in the blanks:
erected, reinforced, design, spans, longest, are
1. The longest spans among lattice trusses … 63m in Russia.
2. The first concrete arch bridge was … in France in 1875.
3. The first … concrete bridges were constructed in 1877.
4. The earliest Russian reinforced concrete beam bridge was built to professor Belelyubsky’s … in 1893.
5. The … spans among continuous beam systems are 105 m in Japan.
6. The longest … among arch bridges are 228 m in the Ukraine.
References: http://www.bris.ac.uk/civilengineering/bridges/Pages/Bridgesasart.html
Unit 4. Beam bridge.
Vocabulary.
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
Lead-in
1. What is a bridge? What obstacles are usual to cross?
2. How long can bridges be? How do bridges differ?
3. What types of bridges according to their functions can you name?
4. Look at the illustrations. Which types of bridges do they match?
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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 river banks 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, this type of bridge is limited by its length, so they rarely span more than 250 feet (76.2 m). But daisy-chaining bridge sections allow to reach 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 following questions:
1. What does a beam bridge consist of?
2. What loads does a beam carry by bending?
3. What materials are frequently used in beam bridge construction? Why?
4. Where are beam bridges most commonly used?
5. What does the distance of a span related to? Why?
6. What the world's longest beam bridges do you know?
Exercises:
1. Decide whether the following statements are true or false according to the text:
1) A beam bridge consists of a rigid horizontal member.
2) Beam is supported at each end by some kind of pile.
3) Less beam bridges are made from concrete and steel to hold out against the forces of compression and tension.
4) Beam bridges are rarely used in highway construction.
5) The biggest limitation of this type of bridge is still its length.
6) The deck of beam bridge is composed of one or several beams, which are supported by piers across the space.
7) Beam bridges typically span the greatest distance.
8) Today beam bridges are not built as foot-bridges.
2) List advantages and disadvantages for the beam construction used. Divide them into two columns:
Limited span; inexpensive relative to other bridge types; does not allow large ships or heavy boat traffic to pass underneath; easy to build; design generally not considered very interesting or eye-catching; used widely in urban and rural settings.
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