GB569537A - Improvements relating to pre-stressed concrete - Google Patents

Abstract

569,537. Reinforced concrete. STENT PRECAST CONCRETE, Ltd., and STENT, D. H. Oct. 13, 1943, No. 16779. [Class 20 (iv)] The ends of the stretched wires b for prestressed concrete members are wrapped around a member c and are clamped between that member and a surface on the means stretching the reinforcement. In the construction shown, both ends of the wire are wrapped around the left-hand member c and are clamped in position by a washer h on a bolt d passing through the member and through the end wall a' of the mould a. The bolthead d<1> bears on a crosshead f which is forced away from the mould by hydraulic rams e during the tensioning operation. The tension is maintained by tightening up a nut g. When the concrete has set the bolt d and a similar bolt engaging the other crosshead are removed and the holes formed are plugged with wet concrete. In a modification the member c is of half-tubular section and the washer h is semi-circular in section, and in other modifications the member c has a groove for the reception of the wires or rods b. In the latter modifications the hole in member e for receiving bolt d is tapered to permit the member to take up small differences in lengths of wires applied thereto, the wires having been pre-bent to their looped form. In the drawing, each member c carries two wires b, one on each side of the bolt, and the mould contains two sets of such pairs of wires. In a modification, Fig. 3 (not shown) one end of each wire is clamped to one member c and the other end to the opposite member. According to a further modification one or more pre-cast concrete units are inserted between the anchoring devices and stretch them apart on partial release of the stretched reinforcement. Such pre-formed struts may be more or less tubular in form and are inserted dry, being amplified by adding wet concrete or grouting to embed the stretched reinforcements.