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Prestressed concrete

The basic concept of prestresssing the concrete consists in introducing the artificially the compressive stresses in a structure before it is loaded. The tensile stresses in the prestressed concrete structure may be reduced to a great extent or even entirely eliniminated depending upon the magnitude of prestressing. In a prestressed concrete structure, the cost of supporting structure and foundation is reduced, dead load of structure is reduced and cracking of concrete is avoided. The high strength concrete and high tensile steel should be used in a prestressed concrete member. According to Indian standards, the cube strength of the concrete used should bot be less  than 35N/mm 2 . The ultimate strength of high tensile steel wires used in prestressing varies from 1500N/mm 2 for 8mm diameter bars to 2350N/mm 2 for 1.5 mm diameter bars. The various methods adopted in prestresssing are as follows: Pre-tensioning The method of providing desired amount of compressive stress in