Earthquakes Will Not Damage This Bridge

A California pipeline bridge has been retrofitted with isolation bearings that damp earthquake shocks. The bridge over Southern California’s Santa Ana River carries the Upper Feeder Pipeline of the Metropolitan Water District of Southern California and is the second in the U.S. to be fitted with isolation bearings. These bearings isolate the bridge superstructure and the 116 in. steel pipeline from earthquake shaking and damp much of the shaking energy that does get through. The vendor claims that replacing the existing rocker bearings with isolation bearings costs only 10% as much as the alternative solution which was to make the bridge stiff enough to withstand the shaking by increasing the lateral stiffness of the columns above the piers and below the superstructure. This article describes the bridge, the isolation bearings, the dynamic analyses done to determine the magnitude of the shaking forces and displacements, and the size of the bearings selected to handle them.