GB699325A - Methods and devices for the manufacture of pre-stressed concrete structural members - Google Patents

Abstract

699,325. Reinforced concrete. PRELOAD CO., Inc. Nov. 6, 1951, No. 25999/51. Class 20(iv) In a method of manufacturing- prestressed concrete structures the components for tensioning a reinforcing member 4 including an anchor member 3 connected to one end of the reinforcing member, an enclosing sleeve 1 temporarily connected to the anchor 3 by a pin 5, and a filler piece 8, are first secured to a form 7 by means of a pulling member 9 which is screwed at one end into the anchor 3 and protrudes through the form 7 at the other end to receive a nut 11 and a washer 10. Concrete is then poured into the form to embed the sleeve 1, partly nested conical rings 21<SP>1</SP> surrounding the reinforcement, and a spiral reinforcement' 13. When the concrete has hardened the form 7 and the piece 8 are removed and the wires are tensioned, with consequent shearing of the pin 5, e.g. by a jack, the nut 11 holding the tension by bearing on an anchor plate 16 which closes the end cavity. Grout is forced into the sleeve 1 and rings 21' through a screwed hole 17 in the anchor plate, a vent tube, not shown, permitting the escape of air from the rings 21<SP>1</SP>. A gasket ensures a tight joint between the plate and the concrete structure. When the grout has set the anchor plate and the pulling member 9 are removed, the cavity being filled with concrete. In an alternative arrangement, Fig. 4, the upper and lower parts of the sleeve 18 are conically and cylindrically stepped respectively, a deeper intermediate piece 21 having a collar 22 to engage the sleeve 18 is used, the parts being secured to the form 7 before the concrete for the main body is poured by means of a bolt 20 and a nut 11<SP>1</SP>. 'When the concrete has set the form 7' is removed together with the intermediate piece 21 and the bolt 20 and the pulling member is screwed into, the anchor member 3. The subsequent procedure is as previously described. In a' further arrangement, Fig. 5, in which prestressing force is transmitted to the concrete through an end anchor plate 28, an anchor 3<SP>1</SP> is screwed into an internally and externally threaded tubular member 25 which, before the wires are tensioned, rests on the inturned bottom edge of a sleeve 24. To stress the wires 4 the head 26 of a pulling element 9 is screwed into the tubular member 25, the element 9 being raised by a hydraulic jack supported on an anchor plate 28. A nut 27 bearing on the plate 28 is screwed on to the member 25 to maintain the tension in the wires. In a modification of the last described embodiment the steel anchor is of cruciform section. In an arrangement for prestressing bars instead of wires, the anchor is of inverted mushroom shape which threadedly receives the pulling element 9 at one end and a reinforcing bar at the other end.