Crack control methods for girder end cracking in a new post-tensioned prestressed concrete I-girder

In a hydropower station, a new modern post-tensioned prestressed concrete I-girder is designed to undertake larger loads in services. However, the increased transverse tensile stresses induced by the improved I-girders with more tendons have raised the possibility of girder end cracking. Several strategies to control these cracks of the targeted girders in this research were studied. The cooling method, which was previously used in the pre-tensioning method, has been applied to simulate the post-tensioning method by extending the length of anchorage. Based on the analytical results derived from the calibrated finite element model, three techniques were compared, including changing the tensioning sequence of the tendons, reducing the initial control prestressing, and using vertical unbonded prestressing bars. To evaluate the effectiveness of crack control techniques, limit values for the concrete principal tensile strains and the stirrup stresses at a girder end were introduced. The results show that the excessive tensile stresses produced by different tendon tensioning sequences and large initial tensioning control stresses contribute to girder end cracks. Changing the tendon tensioning process cannot fundamentally eliminate the appearance of girder end cracks, while reasonably reducing the initial control prestressing of N1 and N2 tendons can decrease the magnitude of principal tension strains at the girder ends. It is suggested that the use of vertical unbonded prestressing bars at the girder ends instead of the previously used bonded prestressing bars can completely control the appearance of cracks at the girder ends.