Prestressed concrete is a modified form of reinforced concrete. This not only overcomes the weakness of concrete, but also makes it possible to take full advantage of the compressive strength of concrete.
word “prestressed concrete“Applied to those reinforced concrete members in which the concrete is subjected to compressive stress before an external load is applied, by inducing tensile stresses in the reinforcement to counteract the tensile stresses in the concrete due to external loads.
Basic Principle of Prestressing
Since the tensile strength of concrete is low, a homogeneous concrete beam has very low flexural strength. To make up for this shortcoming, steel reinforcement is provided near the bottom of the ordinary beam to bear the tensile stress. Although a large area of concrete below the neutral axis retains strength only in position, its tensile strength is neglected in the calculations for flexural strength in the case of reinforced concrete beams.
If the tensile reinforcement of a beam is subjected to tensile stress before an external load is applied, compressive stresses are induced in the concrete of the beam (and this is done by prestressing). Usually the tensile stresses in the concrete due to external loads are completely absorbed or counteracted by the compressive stresses in the concrete, resulting in pressure on the reinforcement. Concrete, therefore, is being used effectively in resisting the tensile stress generated by external loads rather than being neglected as in the 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 because of the higher cost or prestressing and the better quality materials used, it is used in special circumstances, especially for precast members.
In addition to structural precast members such as joists, beams, slabs, columns, girders, etc., prestressed concrete is used for multi-storey buildings.
Prestressed concrete can also be used to build a large number of industrial structures such as silos, roof trusses, water tanks, piles, pipes, nuclear power stations, factories, steel plants, electric sub-stations, etc.