Effects of Pre-Release Cracks in High-Strength Prestressed Girders

This research project investigated the effects of pre-release cracks on girder camber, flexural cracking capacity, and steel stress ranges. The research included a parametric study investigating stress ranges in the prestressing strands in uncracked, cracked and partially cracked girder sections to determine if steel fatigue was a concern. An analytical study also was performed, which modeled several pre-release cracks, including models of two experimental girders that developed pre-release cracks, to determine the effect of various cracks on girder stress and camber. The study concluded that steel fatigue in the prestressing strand is a concern in girders that become cracked in service. A loss of compressive stress is believed to occur in the bottom fiber of the girder because of pre-release cracks, which may result in the section cracking at lower applied load. Finite element modeling determined the loss of compressive stress in bottom fiber of girders with pre-release cracks. Analytical models also showed that pre-release cracks remained local to the crack location, that non-linear stress distributions occurred during the process of crack closure, and that the magnitude of the pre-release crack effects depended on the number of cracks, the crack width, and the crack depth.