Seismic isolation of bridges using elastomeric isolation systems

While seismic design codes are continually being upgraded to incorporate lessons learned from recent earthquakes, seismic isolation presents an alternative strategy for protecting structures from earthquake damage. Rather than make structures ever stronger, causing them to attract more force, seismic isolation focuses on the demand side of the equation. Seismic forces may be reduced to levels within the elastic capacity of new or existing structures, thus minimizing or avoiding inelastic deformation and, therefore, damage. To date, 29 owner agencies have taken advantage of seismic isolation for more than 75 bridges in North America which are completed or under construction. This paper describes how the force-reduction and force-redistribution advantages of seismic isolation have benefited the design and economics of several bridges, both new and retrofitted, in the central and eastern U.S. Performance of isolated structures in earthquakes is also summarized.