Seismic Performance of a Four-Decade-Old Overpass in Southeast Idaho

摘要

Following major earthquakes in the 1970s, 1980s, and 1990s, changes were made to the structural seismic design codes. Structures constructed prior to these revisions need to be evaluated for seismic vulnerability. The US-89 Overpass in Montpelier, Idaho, built in 1971, is the subject of this study. The current seismic design guides were used in conjunction with Open System for Earthquake Engineering Simulation (OpenSees), an advanced finite element computer modeling program, to perform nonlinear analyses of the bridge structure under four displacement time histories. The results show failure of the elements that restrain the lateral movement of the bridge deck. However, the lateral relative displacement between the superstructure and the top of the piers reach a maximum of 11.2 cm (4.4 in.), which is not enough to remove the superstructure from the 1.8 m (6 ft) wide seat. The work presented herein enhances seismic analysis capabilities for existing Idaho bridges and provides valuable information regarding this particular overpass.