Patent GB-740172-A (GB)
Title: Improvement in hydraulic jack for putting under tension and anchoring the re-inforcement wires or rods of pre-stressed concrete
IPC: E04G21/12
Filed: 1953-07-27
Abstract: 740,172. Wire strainers. FREYSSINET, E., and INGENIEURS BUREAU VOOR INDUSTRIE SERVICE N.V., and TANS METAALSCONSTRUCTIES EN ZWAAR TRANSPORT N.V. July 27, 1953 [July 30, 1952; April 15, 1953], No. 20803/53. Class 45. [Also in Group XXX] A hydraulic jack for tensioning and anchoring the reinforcement wires or rods 108 of a prestressed structure comprises a cylinder 101 defining a chamber 138 and containing a main piston 103 for tensioning the wires or rods, an auxiliary piston 121 in a second chamber 134 for driving on an anchoring plug c for the wires or rods and wedges 109 for securing to the jack the wires or rods, and a third chamber 136 located so as to relatively move the cylinder and the main piston in the non tensioning direction when the wires or rods have been tensioned and the anchoring plug secured in position, all the chambers being adapted to be fed with liquid under pressure. The wires or rods are secured to the cylinder in pairs by means of the wedges 109 and pass through an anchoring block b which is engaged through a ring 115 by a head 111 attached to the piston 103. When the wires or rods have been tensioned they are locked in the anchoring block b by means of the plug c. The chamber 134 for the auxiliary piston 121 is formed in the head 111, the piston 121 being moved by liquid pressure and returned to its initial position by a spring 124. The return movement of the piston 103 by liquid pressure in the third chamber 136 causes abutments 114 on the head 111 to engage the wedges 109 to release the wires or rods 108 from the cylinder 101. The abutments are staggered so that the wedges are released in pairs which are diametrically opposite. When the wedges 109 have been freed the cylinder 101 is moved in the tensioning direction to a small degree by a spring 117 so that the wedges can be tightened on the next lot of wires or rods without fouling the abutments. In a modification a spring pressed plunger between each wedge and abutment is used. Liquid is supplied to the chamber 138 through a channel 132 and to the chambers 134, 136 through a channel 133. The chamber 136 is connected to the chamber 134 by a passage 135. To move the piston 121 relative to the head 111, liquid is admitted to the chamber 134, the pressure in the chamber 138 which has previously moved the cylinder 101 relative to the head 111 being maintained. For return movement of the cylinder 101, the chamber 138 is connected to exhaust and liquid entering the chamber 136 from chamber 134 through passage 135 can then return the cylinder. In a modification, valves in the piston 103 are used to control the supply of liquid to chamber 136 automatically. In a further modification each chamber is supplied through a separate channel. In any construction the liquid to the supply channels for the various chambers is controlled by a manually operated distributer. The head 111 has a plurality of channels in its surface so that the wires 108 do not come into contact with it so reducing friction. The ring 105 is also internally tapered so that friction between it and the wires is reduced as tension is increased. The supply of liquid to the channels 132, 133 is provided through detachable thimbles 142, 143. A pressure gauge may be connected to the cylinder 101 to give an indication of the tension applied to the wires.