Unit 3. Reinforced Concrete Bridges
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
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?
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
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