Seismic Response of Bridges with Rocking Foundations Compared to Fixed-Base Bridges at a Near-Fault Site

Abstract

This paper numerically investigates the three-dimensional seismic response of six reinforced concrete bridges hypothetically located in Oakland, California, 3 km from the Hayward fault. Three of the bridges are 17 m tall and three are 8 m tall. Three types of column-foundation designs are studied: (1) columns that form flexural plastic hinges, which are conventionally designed according to CALTRANS seismic design criteria; (2) columns on rocking pile foundations that are designed to remain elastic; and (3) columns designed to remain elastic that are supported on rocking shallow foundations. The bridges with rocking foundations use lead rubber bearings at the abutments to enhance strength, stiffness, and hysteretic energy dissipation. Using two components of horizontal excitation, three-dimensional nonlinear response history analyses are performed for two seismic hazard levels with return periods of 975 and 2,475 years, respectively. At both levels of shaking, the conventionally designed bridges experience substantial inelastic deformations and damage in the columns, whereas the bridges with rocking foundations result in negligible structural damage and a nominally elastic response and small residual deformations.