Effect of the concrete cover thickness ratio on the post-yield stiffness of bridge columns with partially unbonded unstressed steel strands

Abstract

A new self-centering concrete bridge column has been developed by the authors. The proposed bridge column uses unstressed partially unbonded seven-wire steel strands as elastic elements to reduce the residual displacement of the column after a strong earthquake. This research aimed to study the effect of concrete cover thickness ratio on the cyclic behavior of the proposed column. Four large-scale column specimens were tested using lateral cyclic loading. One column was the conventional concrete bridge column. The other three columns were the proposed self-centering bridge columns with varying concrete cover thickness ratios. Test results showed that partial unbonding effectively prevented the strands from yielding. The proposed columns showed post-yield stiffness ratios higher than the conventional column. The concrete cover thickness ratio did not significantly influence the hysteretic energy dissipation and the strain responses of longitudinal reinforcement. However, it had a significant impact on the post-yield stiffness ratio. The post-yield stiffness ratio of the proposed column tended to be inversely proportional to the concrete cover thickness ratio. A relationship was proposed between the concrete cover thickness ratio and the post-yield stiffness ratio for the preliminary design of the proposed column. Based on the relationship, the cover concrete thickness ratio should not exceed 5.1% to achieve a post-yield stiffness ratio of at least 5%, as recommended in the literature to control the residual displacement of a column.