PRESTRESSED CONCRETE (PSC)

In tension Strength of concrete is very low and therefore it is ignored in R.C.C. design. In tension Concrete is acting as a cover to steel and helping to keep steel at needed distance. So lot of concrete is not properly utilized in R.C.C. Prestresseding the concrete is one of the methods of utilizing whole concrete. Wherever tensile stresses are expected in the concrete structural elements in the zones the principle of prestressed concrete is to introduce calculated compressive stresses. Due to loading has to first nullify these compressive stresses when such structural element is used, stresses developed before introducing tensile stress in concrete. Entire concrete is utilized to resist the load in prestressed concrete. In the concrete another essential advantage of PSC is hair cracks are avoided and therefore durability is high. The fatigue strength of PSC is also more than the R.C.C. The deflections of PSC beam is much less and therefore can be used for longer spans also.

PSC is usually used in the construction of large column free slabs, bridges and roofs. PSC sleepers and electric piles are normally used. In PSC, the material used is high tensile steel and high strength steel. The tensioning of wires can be by pretensioning or by post tensioning. Before concreting, Pretensioning consists in stretching the wires and then releasing the wires. The ducts are made in concrete elements In case of post tensioning. Prestressing wires are passed through ducts after concrete of hardens. They are anchored to concrete elements after stretching wires by special anchors.