GB732037A - A method of applying and maintaining pre-tension to the longitudinal reinforcement in pre-stressed concrete pipes - Google Patents

Abstract

732,037. Reinforced concrete. PAGET, R. C. May 6, 1954 [Nov. 27, 1953], No. 33048/53. Class 20 (4). In a method of pretensioning longitudinal reinforcements for concrete pipes, shafts, or tunnels, and of maintaining such pre-tension until the reinforcements are bonded to the applied concrete, the reinforcements and mould parts are supported around a central shaft made in two parts which may be coupled axially by an interrupted thread connection. As shown, the two parts 7, 8 are connected by an interrupted . quick - release threaded joint 9 and carry fast and axially movable circular stress plates 10, 15 having equally spaced -tapered holes 12 to receive the reinforcing wires 13 and securing-wedges 14. The shaft 7, 8 is mounted in bearings 1, 2 supported on mountings 3, 4 fixed to a framework 5, 6, the part 5 being fixed and the part 6 being sufficiently separable therefrom to permit the removal of the finished pipe. A collapsible metal mould 17 is mounted coaxially upon the shaft between the stress plates, joint rings 19, 20, having holes 21 for the wires 13 to pass through being .fitted over the outer ends of the mould. A collar 22 is screwed onto the shaft 8 to bear against the plate 15 and is locked by a pin 24. A hydraulic jack 26, mounted in a thrust block 25, bears against the end of the shaft 8. A number of adjustable anchor bolts 27 are secured to the block 25 and to the plate 15, the turnbuckle portions 28 being removable by the withdrawal of clevis pins 29. The shaft 7 is provided with a pinion which engages through gears in a box 30 with a driving motor 31. To tension the wires 13 pressure is applied by the jack 26 to the end of the shaft 8, the plate 15 being anchored by the bolts 27 to the block 25, and the collar 22 is screwed up against the plate 15 and locked. by the pin 24, whereupon the pressure from the jack is released and the bolts 27 are unfastened from the .plate 15. The shaft is then rotated by the motor 31 while concrete 18 is cast upon the outer surface of the mould to cover the wires 13. After the concrete has hardened the thrust collar 22 is backed away from the plate 15 and the wires 13 are severed close to the outer surfaces of the rings 19, 20. The shaft joint 9 is subsequently disconnected and the part 6 of the framework is retracted, with the end of the shaft supported on the base by temporary cradling, and the shaft 8 similarly supported on the part 5. The pipe is now removed from the apparatus for application of the outer skin elsewhere. Specification 619,304, [Group XXVIII], is referred to.