GB676533A - Improvements in or relating to the tensioning of reinforcing elements for prestressed concrete - Google Patents

Abstract

676,533. Screw jacks. BRAUNBOCK, E. July 15, 1949. [July 16, 1948] No. 18741/49. Class 78 (iii). [Also in Groups I and X] Steel reinforcing elements for prestressed concrete are tensioned by the simultaneous application at one or both ends of stretching and twisting. lf only one wire or bar is twisted its cross section is other than circular (e.g. square or ribbed or flattened round) to increase resistance to slipping. Reinforcements 4 which after tensioning are to be embedded in concrete or cement mortar in grooves 3 of a structural member 2 are anchored at one end to a plate 5a bearing by means of members 6 against an apertured plate 1 abutting the member 2, the wires being gripped between a conically bored member 9 and a wedge 10. At the other end, threaded members 7 constitute jacks engaging threaded holes in a plate 5 bearing similarly against a plate 1 abutting the concrete member. The screw pitch is preferably such that most of the tension is affected by direct stretching. In a modification in which the reinforcements are close to one another plates 5, 5a, are provided at both ends, the jacks being staggered. A portable jack 17 is mounted so as to be located in different horizontal and vertical positions bv means of a channel guide 14 adjustably secured to vertical supports 19 a screw 16 extending from the jack engaging a nut 15 horizontally adjustable along the guide. A conically bored anchor plate 11 is secured bv tenons 12 to plate 1, the wires being wedged in their holes after tensioning and severed from the jack. Guide 14 may be arranged vertically. Specification 556,572, [Group X], is referred to,