Anchorages for post-tensioning
Anchorages are used to fix the ends of the tendons in post-tensioning systems. Various designs are available, depending on the system supplier, but basically they are steel blocks through which single or multiple strands pass and are anchored by wedges. The strands may be tensioned individually or as a group.
The anchorages are cast into the concrete and transfer the entire load from the strands into the concrete. This causes high local bursting forces. To prevent the concrete splitting additional reinforcement is required close to the anchorage.
Where high tensile strength bars used for prestressing, the bars are threaded (either just at the ends or over their whole length) and anchored after tensioning by means of nuts that bear against steel plates set in the concrete. Again addition reinforcement is needed to prevent bursting of the concrete.