GB742737A - Improvements in and relating to bar gripping means for use in the production of prestressed concrete - Google Patents

Abstract

742,737. Clamps. LEE, D. H. March 22, 1954 [May 12, 1953], No. 13229/53. Class 44. [Also in Group X] - A gripping device for prestress bars used in the production of prestressed concrete (see Group X) comprises a collar through which a prestress bar passes axially, wedges within the collar surrounding the bar and two coaxial threaded surfaces on the collar of different diameters. The embodiment of Fig. 1 shows the device applied to a method of post-tensioning concrete. A bar 1 projects from a channel 3 in a concrete member 4 and is engaged by two, or more, oppositely spaced wedges 10 that are flat on all but their bar contacting surfaces which are shaped to have major surface contact with the bar 1. The wedges 10 are embraced in a tapering axial hole 12 in a collar 13, the threaded exterior surfaces of which engage an adjustable thrust collar 18, and a shaft 7 of a tensioning jack through adapting collars 16 and 17. A rectangular thrust-plate 19 with rubber facing 20 takes the thrust of the tension jack and when bar 1 is under tension the thrust collar 18 can be screwed down on to the thrust plate 19 to allow the removal of the tension jack while retaining the bar under tension. In a second embodiment the shaft 7 is connected to the collar 13 by an internal thread and the thrust collar 18 comprises a short cylinder threaded on to the collar 13 and butting against a plain cylinder which acts as a distance piece to the thrust plate. The wedges may have arcuate outer surfaces in cross-section and lie within a tapering aperture of correspondingly circular cross-section in the collar 13. The bar engaging surfaces of the wedges may be grooved to mate with ribs raised on the bar or may be serrated to grip the bar.