SEISMIC ISOLATION IN BRIDGES

In the U.S., the use of seismic isolation in new bridge construction and retrofit projects has been growing as awareness of seismic risk has spread across the country since the 1971 San Fernando earthquake through the 1989 Loma Prieta and 1994 Northridge earthquakes--not to mention the false, but nonetheless consciousness-raising, prediction of a major earthquake on the New Madrid Fault in 1990. To date, isolator bearings have been used to outfit about 75 structures, of which slightly more than half are retrofit projects. Recent projects in New York State, St. Louis, Indiana and New Hampshire that involve the use of several systems demonstrate the use of seismic isolation in retrofitting bridges to better withstand earthquake forces.