GB1092011A - Jack for tensioning cables in prestressed concrete structures - Google Patents

Abstract

1,092,011. Hydraulic jacks. BAUDIN CHATEAUNEUF. March 15, 1966 [March 16, 1965], No. 11292/66. Heading B8J. [Also in Divisions E1 and F2] A double-acting hydraulic jack for tensioning cables in prestressed concrete structures comprises a cylinder 1 with an open end forming a support base 1a, the other end forming a back cylinder-head 1b and a plunger 3 with an axial recess 4 large enough to accommodate a traction lug 6 formed on the end of a cable 7 for prestressing a concrete structure 8. A skirt 17 screwed to the plunger 3 on a stem 11 is adapted to slide over the cylinder 1. Spring-loaded dogs 35 together forming a hollow cone frustum are supported on an annular shoulder 38 in the plunger recess 4 so that the dogs 35 may open radially to allow the traction lug 6 to pass through and close to provide a seating for the traction lug 6. The cable 7 is tensioned by applying fluid pressure, preferably oil, to a chamber 21 to extend the jack and position an anchoring lug 66 adjacent a stress-distribution plate 68, a graduated scale 59 fixed to the cylinder 1 co-operating with a pointer 63 fixed to the skirt 17 enabling the elongation of the cable 7 to be determined. A fork-shaped key 67 is inserted through openings 55, 56, 57 when the anchoring lug 66 is clear of the plate 68 and the chamber 21 pressure relieved. Pressure fluid is then supplied to a chamber 25, the piston 11 and skirt 17 being maintained in their extended position, to return the cylinder 1 within the skirt 17. The cable 7 is then severed at a point between the traction lug 6 and the anchoring lug 66 thus releasing the jack. The traction lug 6 is removed from the open end of the plunger stem 11 and the jack is ready for a further operation.