Patent GB-743708-A (GB)
Title: Process and apparatus for prestressing reinforcing wires for reinforced concrete parts in mass production
IPC: E04C5/12
Filed: 1952-10-24
Abstract: 743,708. Prestressed reinforced concrete. KIRCHNER, I. A. Oct. 24, 1952 [Aug. 27, 1952], No. 26715/52. Class 20(4). Process for pretensioning reinforcing wires for reinforced concrete parts, e.g. beams, which are to be cast in moulds, arranged in a row or preferably several parallel rows on a track 7, Fig. 2, and in which the ends of the wires for a row or rows of moulds running from supply rolls 2 are pulled, in a desired arrangement together from the beginning of the track to the end thereof, the ends of the wires being first pulled through a straightening device 4 and a stationary abutment 5 at the beginning of the track and then fixed to an adjacent mobile abutment 6 mounted on a carriage 8 and this is moved by winding ropes 15 on drums 16 to the end, of the track and fixed to a support member 9, the wires are then secured in the stationary abutment 5 and the support member 9 of the mobile abutment 6 are moved by winding ropes 10 on drums 11 to tension the wires. The stationary abutment 5, Fig. 5, is of stepped cross-section and is anchored or a foundation 21. Slidable clamping members 22 and 23 are provided for clamping the wires for each row of moulds, the wires first being passed through aligned bores in the clamping members and the abutment 5 and then clamped by forcing the slidable members downwardly. The clamping members each carry a rack which meshes with and is moved by a toothed wheel which can be rotated by movement of the crank shown in dotted outline, all the clamping members 22 or 23 for the rows of moulds being movable simultaneously. The bores in the clamping members are wedgeshape in cross-section. In modifications the wire clamping means of the stationary abutment may comprise a series of parallel plates having aligned bores through which the wires pass, alternate plates being displaceable to clamp the wires. The plates are displaced by knocking a wedge through slots in the movable plates. In another form of clamping means the wires are held in slots by wedges 54, Fig. 12, which are forced into position by tightening nuts 58 on bolts 57 against the plate 56 secured to the wedge by a bolt 55. The wedges are removed by screwing bolts 59 against the wall of the abutment after release of the nuts 58. The mobile abutment 6, Fig. 3, has wire clamping means similar to those described for the stationary abutment 5. The abutment 6 is fixedly mounted on a cross-member 35 of the carriage 8 the wheels of which run on the track 7 which has a small ramp 38 adjacent to the support member 9. The support member 9 is slidable on notched rails 40, has a locking pawl 44 for engaging with the teeth of the rails 40 and is adapted to receive the mobile abutment 6 behind a ledge 50 as shown, a hooked latch member 52 holding the abutment rigidly to the support member. After the wires have been clamped securely in both abutments they are tensioned by movement of the support member 9 by ropes 10 attached to bars 48 lying in notches 47 of arms 46 secured to the support member 9. When it is desired to return the mobile abutment to the other end of the track, the latch 52 is released and movement of the carriage 8 up to the ramp 38 lifts the abutment free of the ledge 50 of the support member 9. In a modification each abutment comprises a set of rotatably mounted drums, preferably having grooved surfaces around which the reinforcing wires are wound, diametral or chordal bores or slots being provided through the drums and through which the wirea are passed, the central cores of the drums being axially displaceable to lock the wires in position. In a further modification the stationary abutment is displaceable to tension the reinforcing wires. The mould bed may for example be 100 metres long and as shown in Fig. 2 comprises 20 rows of moulds. The wires may be tensioned up to, e.g. 12,000 kg. per sq. cm.