Experimental investigation on seismic performance of severely earthquake-damaged RC bridge piers after rapid strengthening

This paper proposes a rapid strengthening method for severely earthquake-damaged RC piers. In this strengthening method, high-strength steel bars (HSSB) HTRB600 were used as vertical and horizontal planting rebars anchored into pier footing and pier shaft, and ultra-high-strength concrete (UHPC) was used as grout material. Meanwhile, the UHPC was used to strengthen the damaged plastic hinge region to form the enlarged section to realize the mechanical integrity of the strengthening piers. Utilizing the early strength property of UHPC, the proposed rapid strengthening method can realize the rapid recovery of vertical bearing capacity of severely damaged RC piers, thus ensuring the rapid passage and emergency rescue of bridges after earthquakes. Four severely damaged RC piers under cyclic tests were strengthened and reloaded, and the seismic performance of strengthening and original RC piers was compared, including lateral bearing capacity, lateral stiffness, deformability and hysteretic dissipated energy. Research results show that, for RC piers with only bar buckling but no bar fracture in original specimen, the UHPC enlarged section over strengthens the damaged plastic hinge region, resulting in the plastic hinge of the strengthening piers being relocated to the upper part of enlarged strengthening section. The strengthening pier presents better seismic performance, including lateral bearing capacity, deformability and energy dissipation capacity than original piers. For RC piers with partial longitudinal reinforcement facture, two kinds of strengthening methods, with or without using horizontal planting rebars, were adopted. When using horizontal planting rebars, in spite of presenting asymmetric failure due to the asymmetric damage of original piers, the strengthening RC piers still present comparable seismic performance with original piers. However, the strengthening pier without using horizontal planting rebars presents more distinct pinching effect, lower deformability and hysteretic dissipated energy than original pier. Therefore, the horizontal planting rebars can enhance the force integrity between UHPC enlarged section and pier shaft, and then ensure the seismic performance of strengthening RC piers. Overall, the proposed rapid strengthening method with horizontal planting rebars can not only fulfill the post-earthquake rapid passage demand in short time for the severely earthquake-damaged RC piers, but also ensure the long-term service of strengthening bridge piers by restoring their seismic performance.