What is 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.
- 5. 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.
- 6. 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.
- 7. 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
- 8. 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.