Patent GB-711203-A (GB)
Title: Improvements relating to the production of components of prestressed concrete
Inventor: KORBEL JAN
IPC: B28B23/06
Filed: 1949-02-14
Abstract: 711,203. Prestressed reinforced concrete. MINISTER OF WORKS, and ORLIT, Ltd. March 13, 1950 [Feb. 14, 1949], No. 4010/49. Class 20 (4). [Also in Group V] Components of pre-stressed reinforced concrete are formed by anchoring the wire reinforcements 9b extending through the end walls of the mould 1 to tensioning members 13, 14 at opposite ends of the mould, tensioning the reinforcement by moving apart the tensioning members, maintaining the tension by interposing struts 4 between the tensioning members and, after the concrete has set, stripping down the mould with the struts still in place. The mould comprises an inverted channel section bottom resting on and secured to transverse angle iron supports, and secured to a projecting base plate 2 carrying split tubes 3, shaped sheet steel ends 5 strengthened at 5a and hinged to the bottom 1a by means of coacting lugs 5b, 5c, and end plates 9. The sides 5 are supported in the raised position by levers 7 pivoted to uprights at one side of the mould and fastening by means of notches 7a and cam surfaces 7b to uprights 8 at the other side. The ends 9 are held in place by pins 9a projecting into holes in the side members, and are drilled for the passage of the reinforcements. Steel tubular struts 4 pass through the split tubes 3 which can be compressed to grip the struts, and the strut ends which extend beyond the mould are screw threaded to receive threaded sleeves 4a. The mould rests on a flat bench 10 having fixed abutments 11 at one end and rams 12 located against abutments 12a at the other. The ends 9 are first threaded on the reinforcement wires 9b, the mould erected, and the wires passed through holes in the plates 13, 14, the former resting against the outer faces of abutments 11, and the latter being connected by rods 18 to a plate 15 which slides on guides 16. A bar 17 passes across the inner face of the plate 15 and is engaged at its ends by rams 12. The rods 18 pass freely through plate 14 and are secured by slotted plates 19 fitting in grooves in the rods. The wires are secured to plate 14 by V-shaped clamps 20, given an initial tension by a device comprising a lever with a loosely pivoted edge cam and a rotatable roller, and then connected to plate 13. The wires are then fully stressed by means of the rams which move plate 14 away from plate 15, and the struts 4 lengthened by screwing out the sleeves 4a until they bear against the plates 13 and 14, which may have locating discs 21. When the slotted plates 19 are removed, the mould, wire, plates 13 and 14, and struts 4 form a unit which can be removed from the bench. This unit is stood on a vibrating table, preferably formed of two or more parts, the mould filled with concrete, and pressure applied to the surface of the concrete during vibration. The unit is then removed and the concrete cured, e.g. by steam or immersion in boiling water. The mould is finally opened, difficulty due to the component arching being prevented by the struts, the struts removed, and the wires cut as required. Specification 711,204, [Group V], is referred to.