What is post tensioning

Methods of Post Tensioning

1. Charlie Gupta B.Arch VIII Sem Methods of Post Tensioning

2. What is Post Tensioning? Post-tensioning is a method of producing prestressed concrete, masonry and other structural elements . When the steel is tensioned after concrete placement the process is called posttensioning. When a concrete or masonry element is prestressed , it means that the steel is being tensioned and the concrete or masonry is being compressed. Compression is a force that squeezes or crushes and tension is a force that pulls something apart. Post-tensioning is a form of prestressing. Prestressing simply means that the steel is stressed (pulled or tensioned) before the concrete has to support the service loads.

3. Freyssinet System 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.  

4. Magnel Blaton system In Freyssinet system several wires are stretched at a time. In Magnel Blaton system, two wires are stretched at a time 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.

5. Gifford Udall System This system originated in Great Britain , is widely used in India. This is a single wire system. Each wire is stressed independently using a double acting jack . Any number of wires can be grouped together to form a cable in this system. There are two types of anchorage device in this system . a) Tube anchorages b) Plate anchorages

6.  Lee McCall System: This method is used to prestress steel bars. The diameter of the bar is between 12 and 28mm. bars provided with threads at the ends are inserted in the performed ducts . After stretching the bars to the required length, they are tightened using nuts against bearing plates provided at the end sections of the member. This system has the advantage over others that stressing can be done by stages as it is possible to tighten the nut at any stage.