Post Tensioning System :-
The normally used for post tensioning process are
- Transient system
- Gifford-Udall system
- Magnet Blanton system
- Lee McCall System
Transient System :-
The most widely used method of Prestressing in India and Europe is the transient system. This system consists of a cylinder with a conical interior through which the high tensile wires pass and against the walls of which the wires are wedged by a conical plug lined longitudinally with grooves to house the wires as shown in figure cables are made by wires of Dias, 5 mm to 7 mm. These wires are grouped in units of 8,10,12,14,16, or 18. The wires are held by two cones namely the male cone and the female cones, one end of wires is anchored. The other end is pulled till the required tension is applied. The main advantage of transient system is that numerous wires or strands can be simultaneously tensioned using the double hydraulic jack.
Transient systems was introduced by the French engineer transient, and it was the first method to be introduced. High strength steel wires of 5 mm or 7 mm Dias, numbering 8 or 12 or 16 or 24 are grouped into a cable with a helical spring inside. The spring keeps proper spacing for the wire. Cable is inserted in the duct.
Gifford-Udall System :-
This is system is 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.
- Tube anchorage
- Plate anchorage
Tube anchorage consists of a bearing plate, The anchor wedges and anchor grips. The anchor plate may be square or circular and have 8 or 12 tapered holes to accommodate the individual prestressing wires. These wires are locked into the tapered holes by means of anchor wedges, In addition a grout entry hole is also provided in the bearing plate for grouting. Anchor wedges are split cone wedges carrying serrations on its flat surface. There is a tube unit which is fabricated steel component incorporating a thrust, plate a steel component of the anchorage.
Magnet Blanton System :-
In the magnet Blanton, system, two wires are stretched at a time. This method was introduced by famous engineer, prof, Magnet of Belgium. In this system the anchorage device consist of sand which plate having grooves to hold the wire's ad wedges which are also grooved. Each plate carries eight wires, Between the two ends the spacing of the wire's in maintained by spacers, wires of 5 mm or 7 mm are adopted. Cable consists, of wires in multiples of 8 wires. Cables which as much as 64 wires are also used under special conditions.
Steel sandwich plates flat wedges and a distribution plate are used in the anchorage device as the shown in figure. The wedges for the two wires are driven after completing the tensioning. The distribution plate may be cast into the member at the desired location. Grouting is done after stressing one cable.
You must be logged in to post a comment.