Recorded and Numerical Strong Motion Response of a Base‐Isolated Bridge

Since 1983, 12 Icelandic bridges have been base isolated for seismic protection. Lead‐rubber bearings have been used in all the cases. The Thjorsa River Bridge, built in 1950 and retrofitted with base isolation in 1991, is instrumented by strong‐motion accelerometers. The bridge has one 83‐m‐long main span and two 12‐m‐long approach spans. Only the main span, a steel arch truss with concrete deck, is base isolated. In June 2000, two major earthquakes of magnitude 6.6 and 6.5 occurred in South Iceland; the epicenter was close to the Thjorsa River Bridge. In the first earthquake, a peak ground acceleration of 0.53 g was recorded at the bridge site, and in the second earthquake, a peak ground acceleration of 0.84 g was recorded. The Thjorsa River Bridge survived the earthquakes without any serious damage and was open for traffic immediately after the earthquakes.