Experimental Investigation of Multiple-Strand Lifting Loops

Abstract

An experimental investigation of 28 tests was conduct¬ed to determine the load-carrying capacity of 0.6 in. (15.2 mm) diameter prestressing strand lifting loops. The parameters studied were number of strands in a loop (1, 2, 3, or 4), lifting device (shackle or hook), vertical offset or use of a crushed sleeve, projection of loop from the top of the concrete, and splaying of strand legs. Strand rupture was the primary failure mode, though pullout and side-face blowout became prominent modes in multiple-strand cases. A uniform bond stress of 100 psi (690 kPa) can be used to deter¬mine a safe load. Multipliers of 1.9, 2.8, and 3.3 were determined for double-, triple-, and quadruple-strand loops. Hooks decreased the loop’s capacity by approx¬imately 12% relative to a 2.4 in. (61 mm) diameter pin. A vertical offset of 1 in. (25.4 mm) decreased the loop’s capacity by approximately 42%. Efforts should be made to ensure even loading of the multiple strands within a loop.