Comparative Assessment with Detailed Models of Sliding versus Elastomeric Seismic Isolation in Typical Multi-Span Bridges

Abstract

Recent earthquakes have illustrated the vulnerability of bridges to damage and collapse. One of the emerging tools for protecting bridges from the damaging effects of earthquakes is the use of isolation systems. However, to date, few adequate models exist to evaluate the comparative viability of the two main isolator types: sliding and elastomeric. This paper compares sliding versus elastomeric seismic isolation of a typical Multi-Span bridge to enhance the understanding of their unique impacts on bridge response. The Friction Pendulum System (FPS) and the Lead Rubber Bearing (LRB) are selected as representative examples of sliding and elastomeric isolators, respectively. Detailed isolator models that can account for the in-plane and vertical coupling of the response are developed in OpenSees. Particular emphasis is given to the distinct vertical load dependency modeling of the two isolators. A seismic evaluation of the bridge, isolated in one case with the LRB and in another case with the FPS, is performed for a hazard level of 7% in 75 years using a nonlinear three-dimensional (3-D) analytical model. Maximum isolator forces and displacements, and column drifts are selected as response quantities. The results show that despite attaining similar structural periods, there are notable differences among the two seismic isolation scenarios for the bridge. The FPS placed larger demands on the columns however acquired smaller deformations compared to the LRB. The LRB response is influenced less from the vertical components of ground motions compared to the FPS but susceptible from a stability point of view.