GB1256952A - - Google Patents

Abstract

1,256,952. Casing tube with concreted prestressing members. METALLSCHLAUCHFABRIK PFORZHEIM. 7 Feb., 1969 [24 Feb., 1968], No. 6645/69. Heading F2P. A plastics casing tube which accommodates in concrete therein one, or more, pre-stressed members, not shown, is of helically corrugated form, a continuous helical metal wire, or strip, 12 being fully embedded in the valley parts of the corrugation such that, when the stressing members are stressed, they abrade the valley parts of the tube and bear upon the wire, or strip 12. The tube is made of synthetic thermoplastics and the wire 12 is made of steel. In a modification, Fig. 2, not shown, a shallower corrugation (21) without a wire or strip alternates with a main corrugation which accommodates the wire (22). A casing, which is more nearly cylindrical, Fig. 3, not shown, has the crests of its corrugation flattened. The casing tube 41, Fig. 4, is formed of a helically wound strip of thermoplastic material which is joined by welding its overlapping edges. The profiled strip, Fig. 5, not shown, has positively interlocked edges (53). The wire or strip may be of slightly undulating form or, have thickened portions at regular intervals; alternatively, it may be of strip form of arcuate cross-section and having, on the side which faces the tube axis, axially-spaced bulges. The prestressing members have the abraded plastics material deposited on them to act as a lubricant, while being stressed.