Improvements in or relating to the pretensioning of bodies

摘要

1,122,261. Making beams etc.; bending. E. H. SIDWELL. 13 Aug., 1965 [24 Aug. 1964], No. 34569/64. Headings B3A and B3E. [Also in Division E1] A method of pretensioning a structural body, e.g. a beam, pillar, strut or arch of timber, concrete, aluminium or steel, comprises arranging for the ends of a precompressed member to be fixed relatively to the body. The upper flange of a beam may be pretensioned which has its lower flange precompressed to the same or a different extent. Pretensioning wires 81, Fig. 1, and precompressing wires 91 may be located between formers 1, 21, 51 in the hollow web 131 of a girder 101. Alternatively, the wires 81 may be retained in grooves in the former 51 by a cover-plate. The wires may be located in the hollow flanges (11, 12), Fig. 2 (not shown), of an I-beam, or in a duct in the web 1311 of a continuous beam, Fig. 3 (not shown). Pretensioning wires 8, Fig. 4, may extend beyond the end of a beam for engagement by a plate 51 having holes (54), Fig. 8 (not shown), through which extend precompressing wires 9. A ram (not shown), bearing on the plate 51, tensions the wires 9 and simultaneously compresses wires 8. Side plates (52, 53), or a single plate, if the web is hollow, locate plate 51. Instead of bearing on the wires 8, the plate 51 may engage another plate &c. which bears on the wires. In another construction, Figs. 12 and 14, a hollow flange 11 for the greased pretensioning wires 31 is formed by side plates 30 and a cover-plate 32 fixed by bolts 33. At one end the flange is closed by a plate 36 secured by welding, and at the other the wires bear against a plate 40 locked by plates 41, 42 through which an hydraulic device compresses the wires. The plate 41 is then fixed by welding. The channel or channels in the web may be formed by machining, rolling or extrusion, and each may contain only one wire or member. The lower flange 12 contains four multi-layer wires tensioned and secured by grips (23), Fig. 10 (not shown). The pretensioning wires may be compressed by cooling them in liquid oxygen or nitrogen. The bodies may be additionally pre-tensioned, by fluid pressure in reservoirs in the bodies.