Effect of yielding level and post-yielding stiffness ratio of ED bars on seismic performance of PT rocking bridge piers

This paper proposes an alternative modeling technique for post-tensioned (PT) rocking bridge piers connected with energy dissipation (ED) bars, and investigates the effect of yielding strength level and post-yielding stiffness ratio of ED bars on the seismic response of PT rocking bridge piers. The proposed modeling technique for the bridge pier system consists of a rocking column element and two inelastic rotational spring elements. Three levels of yielding moment are considered for the ED bars, namely values that are half, equal, and two times larger than the rocking (peak) moment of the rocking column. Also, two types of post-yielding behavior are considered for the bridge pier by using two post-yielding stiffness ratios for the ED bars, resulting a negative and a positive post-yielding stiffness behavior of the structure (namely negative and positive systems), respectively. Pushover and quasi-static cyclic analyses are performed in order to check the adequacy of the alternative modeling technique proposed and to investigate the hysteretic behavior of the bridge pier. Furthermore, nonlinear time-history analyses are carried out using twenty LA ground motions. The analyses revealed that the use of ED bars with higher yielding moment strength decreases the peak displacement while it increases the peak acceleration response. The peak base shear obtained with the negative system is almost constant. In the case of positive system, the peak drift and acceleration responses are slightly different than those obtained with the negative system: for example, the differences in the drift ratio and acceleration responses are 0.10% and 7.57%, respectively, when the yielding moment of ED bars is designed as half of the rocking moment. However, the differences become negligible when the ED bars with higher yielding moment strength are considered.