Patent GB-1125176-A (GB)
Title: A new or improved system for securing wires in a stressed condition
Inventor: HARVEY JOHN TERENCE CRAWFORD
IPC: E04G21/12
Filed: 1966-03-31
Abstract: 1,125,176. Wire strainers. P.S.C. EQUIPMENT Ltd. 28 Feb., 1967 [31 March, 1966], No. 14329/66. , Heading F2G. Apparatus for securing and tensioning a tendon consisting of a plurality of wires in a concrete, metal, wood, ceramics, or plastics structure, comprises a funnel-shaped anchorage guide 4 embedded in the structure, an anchor block 5 bearing on the anchoring guide, a plurality of tapered holes in the anchor block, each hole receiving an individual wire and an associated gripping device 23 for holding the wire in a stressed condition once it has been tensioned, a jack 6 for tensioning the wires, bearing against the anchorage guide or anchor block, an axial bore 45 through the jack receiving a central wire or group of wires 7, 8, 9, gripping means 46, 47, 48 disposed in the outer end of said bore remote from the anchor block for gripping the wires during tensioning, and a plurality of gripping devices 51, 52 arranged in recesses around the peripheral outer wall of the jack, each receiving one of a peripheral group of wires for gripping the wires during tensioning. The anchorage guide is provided with radial strengthening ribs (12), Figs. 5 and 6 (not shown), and may receive a conical sleeve (15) for spacing two outer rings 10 and 11 of eighteen and twenty-four wires respectively. The jack comprises a head 28, which is secured to a stationary annular piston 40 and bears against the anchor block. The piston is disposed between inner and outer tubes 41 and 42 closed at their outer ends to form an annular cylinder and defines hydraulic chambers 43, 44 for extending or retracting the cylinder. Each wire of a central group of the tendon wires, consisting of a single wire 7, a ring of six wires 8 and a ring of twelve wires 9, passes through its associated gripper device 23 in the anchor block, along the central bore of the jack, and through its associated gripper device 46, 47 or 48 housed in a block 49 at the rear of the jack. Resilient devices 31 mounted in and around the jack head act between a pressure plate 31 or an abutment and the gripping devices of the anchor block to urge said gripping devices into engagement with the wires. Each of said resilient devices, Fig. 2a (not shown), consists of two interconnected coaxial tubes (34, 35) housing a coil spring 37. A subsidiary gripping device 39 associated with the resilient devices of the central wire or group of wires retains the grippers in position during initial location of the jack. Each wire of a peripheral group 10 and 11 of the tendon wires passes through its associated gripper device in the block and into its individual gripping device located in the peripheral wall of the jack. In a similar embodiment. Figs. 9-11 (not shown), a tendon consisting of nineteen wires is stressed by similar apparatus. In this embodiment, the conical spacing sleeve (15) of the previous embodiment is omitted and an adapter is inserted between the jack head and the funnelshaped anchorage guide, said adapter housing the resilient devices 31 associated with the gripping devices of the anchor block. On extension of the jack, all the individual wires of the tendon are tensioned simultaneously, the anchor block gripping devices holding the wires in the stressed condition on retraction of the jack. Alternatively, since each wire is individually gripped, groups of wires of the tendon may be tensioned successively. This latter mode of operation permits the use of a jack not having the load capacity to tension all the wires simultaneously. The other end of the tendon (not shewn) may be either axially anchored or tensioned by similar apparatus.