GB690986A - Improvements in or relating to jacks - Google Patents

Abstract

690,986. Wire strainers. STRESSED CONCRETE DESIGN, Ltd. April 5, 1950 [April 9, 1949], No. 9706/49. Class 45 Relates to a jack device in which an outwardly directed thrust force exerted by a hydraulic or pneumatic jack upon a crosshead 5 at one end of the jack is transmitted by a pair of links 20 to a stressing member 10 extending transversely of a thrust framework 3, against which the other end of the jack is supported, the ends of the links 20 which are adapted to be connected to the stressing member being formed with loops through which the ends of the stressing member respectively project, the front edges of the stressing member having recesses 12 into which the closed ends of the loops fit to prevent disengagement of the loops in the stretching operation. The crosshead is connected to the jack so as to be capable of pivoted balance-lever movement, two return springs 9 for the jack being arranged to act on the crosshead at opposite sides of the jack to urge the crosshead towards its normal position at right angles to the axis of the jack. The cylinder 1 of the jack, Fig. 2, is,attached at its base to the thrust framework 3 which comprises four rods 32 attached to plates 30, 31 at each end and the ram 2 of the jack is pivoted to the crosshead 5. The crosshead is detachably connected by, the links 20 to the stressing member 10 which is positioned between the rods 32 of the thrust framework. Wires to be strained are connected to the stressing member by wedges'15 engaging tapered grooves in the member. The wires pass through an anchoring block 4 by which they can be locked in position by wedges after straining and the thrust framework is positioned on this block. The links 20 are formed of strip metal-with the ends bent over and welded into loops 22 which engage recesses 11, 12 in the members 5 and 10. In a modification, Fig. 4, which is intended to strain wires around a cylindrical structure the thrust member is replaced by a wheeled carriage having a member 29 at its end opposite to the jack in which one end of each wire is gripped by wedges, the wires then pass through grooves in a plate 38 and round the cylindrical structure, through a second set of grooves in the plate 38 and then to. a stressing member 40 arranged underneath the carriage and attached by links 20 to a crosshead 5 on a jack ram as in the first embodiment. With this arrangement the strain is applied equally to both ends of each wire, the carriage moving on its wheels to permit this. The two ends of each wire are arranged one over the other in the member 38 and alternate pairs pass through the grooves in opposite directions to prevent torsion on the member 38. The member 38 also has a threaded bolt which bears on the structure while the initial pair of wires are being strained to prevent the member tilting. The carriage has four screwed spindles 45 by which it is initially positioned after which the wheels 42 which are slidably mounted are lowered into position and the spindles disengaged. Specification 690,981 is referred to.