A Moslehi Tabar - Assistant Professer, Department of Civil Engineering, Tafresh University, Tafresh, Iran.
M.R Rahbar - Permayon Advanced Strengthening Co., Tehran, Iran

Bridge mass concrete piers had widely been used during past decades. This kind of pier is very vulnerable to earthquake excitations due to its excessive weight and inadequate reinforcement. A convenient way to promote the performance of this kind of pier is to apply a prescribed compressive stress using post-tensioning technique. The present paper is to investigate the seismic response of a typical mass concrete pier rehabilitated using this method. In the numerical case study carried out in the paper, it is shown that a prescribed compressive stress about five percent of the piers axial strength can promote the lateral load-carrying capacity by 60 percent. Moreover, the piers with originally brittle behavior can show ductility using adequate post-tensioning. The capability of the rehabilitated piers to reveal stable non-linearity is resulted in a seismic response modification factor of 2.9, approximately. This value is comparable with unity considered for the existing piers. The nonlinear analysis conducted under cyclic loading confirms that the efficiency of this method does not considerably degrade during the loading excursions. Finally, a simplified method is proposed to estimate the prescribed compression needed to achieve required strength and ductility

Seismic rehabilitation; Mass concrete pier; Post-tensioning technique