A temperature of about 460⁰c was necessary to induce an initial stress of 55 percent of ultimate tensile strength heating time being 40-90s at 30v and 300-1100 A and Empirical relations for estimation of current, voltage and power requirements of transformer are reported by Graduck.

Hoyer?s system of prestressing involves pulling out of wires between two bulkheads which are separated at large distances in order to produce a larger number of beams in an individual alignment, concrete is to be poured by providing appropriate shuttering between beams and n wires are united after hardening of concrete and cutoff.

The method of tensioning Manel-Balton system involves hydraulic jack tensioning two wires at a time, arrangement of Magnel-Balton system constitutes of a rectangular cable section provided with layers of wires of diameter about 5mm to 8mm such that each layer is supplied with four wires and arrangement of wires in geometric pattern is to be considered by supplying spacers/grills at uniform intervals throughout length of cable, an adequate resistance against friction for wires in of sandwich plates.

Tensile stresses of up to 850n/mm² were developed in steel by expansion concrete results of laboratory investigations of several types of chemically pre stressed elements, such as beams, slabs, frames, columns, pipes and hyperbolic parabolic sheets have demonstrated feasibility of chemical pre stressing.

Freyssinet system of prestressing involves arrangement of high tensile steel wires of about 12 in number with diameter of 5mm to 8mm forming a group into a cable, cylinder is provided as an anchorage and it has a conical hole at its centre provided with heavy hoop reinforcement se cylinders are is provided as an anchorage and it has a conical hole at its centre provided with heavy hoop reinforcement.

Thermo electric pre stressing helps to cause on initial stress in tendons of magnitude from 500 to 600n/mm² and concrete is placed in moulds only after temperature of wires falls below 90degrees.

High early strength concrete is often used in factory to facilitate early stripping reuse of moulds and when concrete attains sufficient strength, jacking pressure is released and edge of tendon at its eir side is formed to an abutment and its or edge is to be pulled with application of jack.

Tendons are spliced in case of continuous pre stressed concrete members to gain continuity and various types of splices used as tendons are screw connector, torpedo splices, clamp splice and wrapped splice and torpedo splices consists of triple wedges for securing wires and entire unit is covered and protected by a sleeve and this type of splice is largely used for splicing cold drawn wires.

The commonly used mechanical devices are weights with level transmission, weight without lever transmission, geared transmission with pulley blocks; screw jacks without gear drives, wire winding machinery and mechanical devices are generally used for imparting prestress in concrete members which are prepared in large amounts in big factories.

In this method tendons are heated through high tensile wires and by allowing electric current to flow through it, this process is referred as rmo electric pre stressing, in erstwhile U.S.S.R, electro rmal method has been widely used since 1958 for pretensioning bar reinforcements of precast units.