Seismic performance of tall pier bridges retrofitted with lead rubber bearings and rocking foundation

Abstract

Bridges with 40 m or taller piers are commonly constructed in southwest China that is a region of high seismicity. Since it is common practice that the superstructure of such bridges is directly placed on rubber bearings without additional constraints, sliding between the girders and the bearings may occur in the events of strong earthquakes. With the focus on the bridges with tall piers, this paper investigates the effectiveness of different seismic retrofitting measures including lead rubber bearings and rocking foundations in mitigating the seismic responses of bridges. Based on the predetermined damage states for different structural components, the seismic responses of prototype bridge with rubber bearings, as well as retrofitted with lead rubber bearings (LRBs) and rocking foundations, are computed and compared subjected to ground motions with PGA level specified in current Chinese specification. The results show that for the prototype bridge, excessive deformation of rubber bearings and considerable damage of pier columns will happen under strong earthquake motions considered herein. While LRBs are capable of controlling the relative displacement between girders and bearings, reducing the probability of unseating, they cannot suppress the seismic demands of pier columns effectively. On the other hand, when rocking foundations are employed, the dynamic performance of piers is improved significantly, and the piers are expected to remain elastic during strong earthquake excitations. The reason is that LRBs could only reduce the seismic inertial force of superstructure, while the rocking foundation is able to isolate that caused by pier columns as well, which is significant for tall pier bridge. Additionally, once the tall piers start to rock, seismic responses, e.g., deformation of bearings and curvature of piers, tend to be similar and independent of input motions, improving the predictability of post-earthquake state of these bridges.