The pre-stressing heads are the elements designed to exert a reaction force to the amount of pull resulted of the tension of strands. The system is usually comprised of an active stressing head and a passive stressing head, both designed to be anchored to foundation pits.
Other version of the system has also two reacting columns which are disposed in parallel to the casting bed. In this case, the pre-stressing heads are not designed to transfer the force to foundation pits, but to the reacting columns.
The passive stressing head is a kind of buttress consisting of a steel structure anchored to the concrete foundation pit. It includes a matrix of drill holes to thread the strands in accordance to the precast elements to be casted.
The active stressing head has the same steel structure and features a set of hydraulic cylinders to push the movable mask with the same matrix of drill holes. These cylinders allow removing the remaining tension of the strands when the concrete has hardened enough. After this, it is possible to cut the strands safely.
The pre-stressing heads are designed according to the maximum amount of tension required to be resisted.