DYWIDAG Prestressing Systems using Bars
DSI's small and lightweight jacks are easy to operate and facilitate the stressing operation. Heavy lifting aids are usually not necessary. The jack is pushed over a pull rod coupler that is threaded onto the bar protrusion behind the domed anchor nut. The jack is then fixed with a pulling nut. The tension load is hydraulically transferred. The domed anchor nut is tightened by an internal wrench. Special stressing jacks are used for 47 WR bars.
Straight tendons are generally stressed from one end only. In order to reduce friction losses (especially in draped tendons), stressing is recommended from both sides.
The prestressing load can be increased or lowered by reinstalling the jack at any given time until the tendon is fully grouted. This allows partial stressing. Several controls during and after the stressing operation serve for checking the effective stressing load:
- bar protrusion at the anchorage before and after stressing to evaluate the effective elongation
- counter control for elongation during stressing operation
- gauge control for hydraulic pressure
To comply with exceptional high demands on accuracy, for example in the case of very short tendons, special accessories can be applied to minimize the influence of alignment tolerances.
The durability of bonded post-tensioned construction depends mainly on the success of the grouting operation. The hardened cement grout provides bond between concrete and tensile elements as well as primary long term corrosion protection (alkaline medium) for the prestressing steel.
DYWIDAG-Systems International has developed a grouting operation based on highly plasticized grout with thixotropic properties, and utilizes durable grouting equipment. Advanced methods such as pressure grouting, post-grouting and vacuum grouting are the results of many years of development.
Grouting is always carried out from a low-point of the tendon. This can be one of the anchorages with a grout cap with grout inlet. Grouting can also be carried out along the tendon by using an intermediate grout saddle. All grouting components are threaded to facilitate an easy, fast and appropriate connection.