Reinforced-concrete bridges

 Reinforced-concrete bridges are the ones having concrete superstructures. The support of such bridges are usually concrete or rubble concrete, while the ones of overpass bridges are made of reinforced-concrete due to their small cross-size which insignificantly restrain the space.

 Reinforced-concrete elements may be differently shaped. That's why systems and constructions of reinforced-concrete bridges are so diverse. Beam systems became most widespread - there are simple, continuous, suspended beams. Different web beam, arched and combined systems are commonly used. According to the method of construction, superstructures can be monolithic, i.e. concreted directly at the site; precast, assembled of prefabricated elements; precast monolithic, which are a combination of precast elements, monolithic concrete and reinforced concrete.

 Reinforced concrete as a building material was obtained in the latter half of the XIX century. The Frenchman Joseph Monier is considered to be its inventor. In 1867 he was granted the patent for flower planter made of concrete intensified with iron ties. In 1873 he received the patent and in 1875 the first reinforced-concrete footbridge with the length of 16 m and width of 4 m was constructed in a private park.

 Successful usage of Monier system bridges brought along new inventions; independent inventors and building companies made a lot of different suggestions. Bridge structures with rigid reinforcement appeared, in which reinforcement was carried out with angles, channels, rails, and even lattice trusses. Main advantage of rigid reinforcement was facilitation of work execution: formwork could be hung up to previously constructed reinforcement.

 Rigid reinforcement was used in superstructures of Richard Wünsch system (Hungary, 1897). They have one row of reinforcement laying along lower curved surface of vault, another row - along upper flat surface. Both reinforcement rows are brought to back edge of abutment where they are connected with rising piers.

Lattice trusses are used as reinforcement in construction of M. Moeller (Germany, 1897) superstructure system. Cross section of superstructure is ribbed, and the slab is located at the bottom.

In early 50s of the 20th century construction of cantilever frame bridge systems began in Western Europe. In these systems superstructures (framework beam) are rigidly connected to the base that provides favorable conditions for their balanced concrete casting (balanced erection). That's why cantilever frame systems became widely spread later.

Nowadays research and development work is being carried out on the planned bridge crossings across the Strait of Gibraltar (Spain-Morocco), the Strait of Messina (Italy - Sicily), the Bering Strait (Russia - Alaska, USA), the La Perouse and the Strait of Tartary (Russia) and others, which consider the use of superstructures with spans up to 5000 m. Such span are rather possible for metal superstructures. Reinforced-concrete superstructures with large spans are economically inconvenient and technically unlikely to realize. It is because weight strength of reinforced-concrete is less than of metal. Because of this, the proportion of the constant load in the total load, perceived by the superstructure, increases.