ISOLATION DESIGN: AID TO BRIDGE REHABILITATION IN LOW TO MODERATE SEISMIC ZONES

Seismic isolation is an alternative strategy for protecting structures from earthquake damage. It focuses on the demand side of the equation, reducing seismic forces with the goal of limiting them to the elastic capacity of new or existing structures, thus minimizing or avoiding inelastic deformation and thus, damage to the foundations and columns. In addition to reducing the seismic forces, the unique bilinear force-deflection characteristics of seismic isolation systems also permit the engineer to control, within limits, the distribution of lateral loads. To date, 23 owner agencies have taken advantage of seismic isolation with more than 40 bridges in North America completed or under construction. This paper describes how isolation benefited the rehabilitation of some of these bridges in low and moderate seismic zones, particularly the Midwest and East.