GB629872A - Railway sleepers and other articles made of pre-stressed reinforced concrete, and a method of and apparatus for manufacturing such parts - Google Patents

Abstract

629,872. Pre-stressed reinforced concrete articles, e.g. poles, sleepers. FREYSSINET, E. Dec. 24, 1947, No. 34176. Convention date, Feb. 14, 1942. [Classes 20(i)and 20(iv)] [Also in Group XXX] Pre-stressed concrete articles, especially short articles, e.g. small poles, railway sleepers, are made by forming the body in two parts separated by a slit and joined by the reinforcements, pulling the two portions apart to tension the reinforcement and widen the slit, and arranging a wedge, preferably of caulked mortar, in the slit. As shown a sleeper is formed in a mould 1, which is divided by a partition 2, by placing a block b, b 1 at each end winding reinforcements a, a 1 of steel of high elastic limit and filling the mould with concrete. Each layer a, a 1 of reinforcement is formed from a wire the two ends d, e of which hook together, and between the points g, g 1 the wire is covered with bitumen and fitted with gutters 3 at the curves to permit movement during stretching. This arrangement of reinforcement permits of reducing the section of the sleeper in the middle to reduce the weight. When set the sleeper is gripped between pairs of jaws 15 15, 16 16 by means of bolts 17 and nuts 18, when slipping is prevented by the sloping sides of the sleeper and by the interengaging grooves 19, and the whole is placed in two cages 20, 21 which are moved apart by jacks 22. Wedges 25 are placed between the jaws 15, 16 and the inclined edges 23, 24 of the cages with lead plates 35 between and keys 36 prevent the wedges from slipping. The cylinders of the jacks are adjustable vertically by bolts 29 and nuts 28 and are held in the cage by screws 27. When the required tension is applied, and the gap between the sleeper parts widened, the partition 2 is removed, and the gap filled with a rich dry cement mortar by caulking with a hammer and surrounded by a bending device with uprights 31 adjustably connected by screwed rods 32 and nuts 33 and with horizontal wedge members 34 between. The jacks &c. are then removed. The concrete blocks 6, 6 1 are formed in two sections 4 separated by a slit 7 in a frame, in the inner face of which the reinforcement 5 has been wound, with ends 5a, 5b anchored at top and bottom respectively, and a hoop of steel wire containing a conical froming placed in each half when the concrete has set. Wedges 9 are driven between liners 13 into cavities 8 at the ends of the slit 7 to force the block halves apart and tension the reinforcement, and the slit 7 filled by caulking with mortar and the wedges removed. Alternatively the reinforcement may be fitted to the cast blocks and then tensioned. When the sleeper is finished elements C of dry hard wood &c. are inserted in the frusto-conical cavities, formed in the block halves, and serve to receive the coach screws &c. The sleeper may be curved in the vertical plane as shown in Fig. 1.