Patent GB-764784-A (GB)
Title: Method and apparatus for the production and delivery of pre-stressed ferro-concrete objects
IPC: B28B23/04
Filed: 1955-02-21
Abstract: 764,784. Reinforced concrete. SOC. DES ATELIERS ET CHANTIERS MARITIMES DE FEDALA. Feb. 21, 1955 [Feb. 20, 1954], No. 5190/55. Class 20(4) A concrete article, more particularly a "tetrapod" used, for example, in port and harbour constructions is pre-stressed by pre-tensioned reinforcement wires, the tensioning being effected by anchoring the outer ends of the non-vertical reinforcements, which radiate from a ring common to them and to a vertical set of reinforcements, and pulling the vertical set upwardly to produce equal stresses in all the  reinforcements. The concrete is then poured into shuttering surrounding the reinforcements and the tension is held until the concrete is set sufficiently to bond, after which the wires are cut from their anchorages, the shuttering taken away and the " tetrapod " removed. The " tetrapod " 35 is reinforced with three sets of wires attached to anchor discs 43 and a vertical set attached to a disc 46 depending from a carriage 38 and operated hydraulically. The discs 43 are carried on adjustable screwed members 42 articulated to the apex fittings 33a of a tripod 33 having horizontal struts 34. The upper ends of the tripod legs 33 are secured to one end of a track 36 having rails 7 on which the carriage 38 runs between buffers 39, the other end of the track being supported by a column 37. The wires are tensioned and the carriage is traversed by means shown in Fig. 3. In operation, the carriage, being positioned centrally relatively to the tripod 33, the reinforcement wires are secured to the discs 43, 10, the screwed adjustment 42 being used to bring the common ring into vertical line with the rod 9. The hydraulic tensioning means are suspended by a trunnion ring 3 from girders 1 in the carriage 38, but operation of the valve 14 to admit fluid beneath the piston 4 first makes the cylinder 6 descend on the piston until lugs 6a rest upon the track rails 7. the carriage itself thus being relieved of the strain of the tensioning. Further admission of fluid raises the piston 4 and. with it, the rod 9. Pressure is constantly admitted to the space above the shoulder on the piston 4 but is overcome by the pressure on the large area beneath the piston. When the latter space is vented to exhaust 32 by manipulation of the valve 14. the pressure on the shoulder raises the cylinder 6 from the track rails 7. The hoisting of the " tetrapod " from the tensioning position, after the wires are cut and the shuttering removed, is effected by attaching a hook, not shown, to the disc 10 and admitting fluid, by the valve 16, to the underside of a piston 8 iri a cylinder 4a integral with the piston 4, the trunnion mounting 2, 3 allowing the load to swing slightly and thus avoid the damage which would result from a rigid mounting. The hoisted "tetrapod" is conveyed to a removal truck 48 by traversing the carriage 38, this being done by a hydraulic cylinder and ram 18, 19 having two sets of sheaves 21. 22 and 25. 26 for two cables 46 which pull the carriage 38 in a direction determined by the valve 31. The tensioning of the wires is constant during the setting period, since the pressure fluid is at constant pressure, and a warning whistle or the like may be provided to give alarm if the fluid pressure fails.