Seismic performance of self-centering rocking bridge piers using inclined tendons

Self-centering (SC) rocking piers can bring the bridge back toward its initial position by employing restoring forces made by post-tensioned tendons. The tendons can be vertically post-tensioned or made at any angle other than 90° to the horizontal direction. However, the axial stiffness of the inclined tendons may play a more significant role in resisting the lateral seismic load than vertical tendons, which increase their elongation. Therefore, inclined tendons yield sooner, and their allowable initial stress has a lower value to prevent tendons’ yield. There is an angle corresponding to the zero post-tensioning (PT) force, and the tendons cannot become closer to the horizontal direction than that. In the present study, the force-displacement relationship of the SC rocking pier, which is post-tensioned with a tendon at an arbitrary angle, is derived. Moreover, the equation determining the elongation of the tendons is obtained, which gives the minimum allowable angle of the tendons. Cyclic analyses were performed to investigate the behavior of the model. Then, non-linear incremental dynamics analyses were conducted using selected earthquake records. Fragility curves considering the maximum drift and residual drift as engineering demand parameters (EDPs) were derived. The results showed that using SC rocking piers with oblique non-post-tensioned tendons significantly reduces the residual drift, reducing the probability of emergency usage interruption even more efficiently than the corresponding vertically post-tensioned pier. SC rocking piers with non-post-tensioned oblique tendons are proposed as a suitable alternative for SC piers with post-tensioned vertical tendons.