Prestressed concrete is a modified form of reinforced concrete. it not only eliminates the weakness of concrete, but also makes it possible to take full advantage of compressive strength of concrete.
The term “Prestressed Concrete” is applied to those reinforced concrete members in which concrete is subjected to compressive stresses, before the external load are applied, by inducing tensile stresses in the reinforcement to counteract tensile stresses in the concrete caused by external loads.
Basic Principle of Prestressing
Since the tensile strength of concrete is low, a homogeneous concrete beam has very little flexural strength. To offset this deficiency, steel reinforcement is provided near the bottom of simple beams to carry the tensile stresses. However, a substantial area of concrete below the neutral axis merely retains the reinforcement in position, but its tensile strength is neglected in the computation for the flexural strength in case of reinforced concrete beams.
If the tensile reinforcement of beam is subjected to tensile stresses before applying the external loads, then compressive stresses are induced in the concrete of the beam (and this is done by prestressing). Usually the tensile stresses in the concrete caused by the external loads are completely absorbed or counteracted by the compressive stresses in concrete, resulting from prestressing the reinforcement. The concrete, therefore, is being used effectively in resisting tensile stresses produced by external loads rather than being neglected as in case of reinforced concrete.
Applications of Prestressed Concrete
Prestressed concrete can be applied to almost all concrete constructions where ordinary reinforced concrete is used. But due to high cost or prestressing and better quality materials used, its use is made under special condition, particularly for precast members.
In addition to structural precast members, viz., joists, beams, slabs, columns, girders, etc, prestressed concrete is used for the framed multi-storeyed buildings.
A large variety of industrial structures such as silos, roof trusses, water tanks, piles, pipes, nuclear power stations, factories, steel plants, electric sub-stations, etc can also be built in prestressed concrete.