SEISMIC RESTRAINER DESIGN METHODS FOR SIMPLY SUPPORTED BRIDGES

Existing restrainer design methods recommended by the American Association of State Highway and Transportation Officials (AASHTO) and the California Department of Transportation (Caltrans) to prevent unseating in simply supported bridges subjected to strong earthquakes were evaluated. Three new methods with different levels of complexity were developed: W/2, modified Caltrans, and the equivalent linear static design for restrainers. The adequacy of different design methods was assessed using a nonlinear response history analysis computer program. Effects of different earthquakes, substructure stiffness, bearing strength, seat width, and skew angle were studied. It was found that in bridges with reinforced concrete pier caps the inherently wide supports help prevent unseating, and simple methods such as the AASHTO and W/2 methods are satisfactory. In bridges with steel pier caps that provide narrow bearings the modified Caltrans method is recommended. The relatively involved equivalent linear static design for restrainers method is a more rational design procedure and leads to considerably fewer restrainers than others.