Fluid operated jacks

Claim 1

A stressing device for stressing elongate reinforcing elements in concrete structures, comprising a base plate adapted to bear with one face against the structure, a plurality of tapered bores in the base plate through which the reinforcements may pass which bores widen outwardly away from the said one face, two or more tapered anchoring segments for disposition in each tapered bore, a homing jack in axial alignment with the base plate, said jack comprising an annular cylinder formed with an open end which bears against the base plate, a piston in the cylinder movable under fluid pressure towards the base plate and openings in the piston and in the cylinder in register with the bores in the base plate for passage of the reinforcements therethrough, and a stressing jack in axial alignment with the homing jack, the stressing jack comprising a cylinder block bearing on the homing jack, a central bore in the cylinder block, an annular cylinder in the end of the cylinder block remote from the homing jack and an annular piston disposed in the cylinder and movable under fluid pressure away from the homing jack, and a tensioning member movable with the annular piston of the stressing jack and having means for gripping the reinforcements, so that when the device is in use and the reinforcements are gripped by the tensioning member, movement of the piston in the stressing jack away from the base plate causes the tensioning member to apply a tensioning force to the reinforcements, and movement of the piston in the homing jack towards the base plate causes the piston to engage the tapered anchoring segments and drive said segments into the tapered bores in the base plate to fix the position of the reinforcements with respect to the base plate.