Numerical Investigation of Cracks at Girder Ends of Prefabricated Post-Tensioned Prestressed Concrete I-Girders

Prefabricated post-tensioned prestressed concrete (PTC) girders with high degrees of prestressing have been developed continuously in recent bridge designs to reach longer spans, higher quality, and larger load-bearing capacity. However, during the prefabrication process, several inclined and horizontal cracks were observed at the ends of a new style post-tensioned concrete girder, which could have a negative impact on the girders' longevity. In this study, a nonlinear finite element analysis technique was utilized to illustrate how concrete reacts and the mechanisms behind typical cracking patterns during the actual post-tensioning sequence. The prestressing load of a PTC girder was simulated with an improved cooling temperature method that accounts for immediate prestress losses. The field of principle tensile strain patterns and primary strain trajectories explained the overall mechanism underlying typical cracking behaviors. The results showed that the horizontal cracks under the anchorage plate (behavior 1) were generated by the bursting force, whereas the inclined cracks (behavior 2) and the horizontal cracks between the strands N1 and N2 anchor plates (behavior 3) were caused due to the spalling force. The effects of self-weight, girder end forms, as well as the transfer length of the prestressing strands, were discussed. The result demonstrates that both the self-weight and girder end shapes have a considerable effect on the behaviors of the anchorage zone. It is suggested that the transfer length of the anchor head be greater than 26 times of strand diameter to achieve the same effective stresses as the theoretical values.