Freyssinet system was introduced by the French Engineer Freyssinet and it was the first method to be introduced. High strength steel wires of 5mm or 7mm diameter, numbering 8 or 12 or 16 or 24 are grouped into a cable with a helical spring inside. Spring keeps proper spacing for the wire. Cable is inserted in the duct.
Anchorage device consists of a concrete cylinder with a concentric conical hole and corrugations on its surface, and a conical plug carrying grooves on its surface (Fig. 3). Steel wires are carried along these grooves at the ends. Concrete cylinder is heavily reinforced. Members are fabricated with the cylinder placed in position. Wires are pulled by Freyssinet double acting jacks which can pull through suitable grooves all the wires in the cable at a time. One end of the wires is anchored and the other end is pulled till the wires are stretched to the required length. An inner piston in the jack then pushes the plug into the cylinder to grip the wires.
In Freyssinet system several wires are stretched at a time. In Magnel Blaton system, two wires are stretched at a time. This method was introduced by a famous engineer, Prof. Magnel of Belgium. In this system, the anchorage device consists of sandwich plate having grooves to hold the wires and wedges which are also grooved. Each plate carries eight wires. Between the two ends the spacing of the wires is maintained by spacers. Wires of 5mm or 7mm are adopted. Cables consists of wires in multiples of 8 wires. Cables with as much as 64 wires are also used under special conditions. A specially deviced jack pulls two wires at a time and anchors them. The wires with the sandwich plate using tapered wedge.
Methods of Post Tensioning 