Strand debonding for pretensioned bridge girders to control end cracks

Characteristic cracks occur at prestressed bridge girder, ends during prestress release due to the transfer of the prestress force to the concrete. This research investigated the quantitative and qualitative impact of strand debonding on cracking through nonlinear finite element analysis' (FEA) and plant observations. The analysis included plastic behavior of concrete and stress redistribution after tension induced cracking. Prestressed bulb tee girders, 54, 72, and 82 in. (1372, 1829, 2083 mm) deep, were analyzed with 25, 35, and 50% of the strands debonded at the girder end. The tensile strains were used to judge cracking, and were compared with cases that had no debonding. The results showed that 25% debonding can completely eliminate the excessive concrete tension strains associated with cracks in critical locations. For cracks in other locations, related strains were considerably reduced with 25 to 35% debonding, and eliminated with 50% debonding. The selection of the strands to be debonded significantly impacts cracking. Recommendations on debonding strands and desirable bonded strand patterns are presented.