Validation of AASHTO bearing stiffness for standard precast concrete bridge girders

Precast American Association of State Highway and Transportation Officials (AASHTO) concrete bridge girders are often supported at the ends of elastomeric bearing pads. The bearing pad-bridge girder interface defines support boundary conditions that may affect the performance of the bridge. In this study, finite element (FE) modeling was used to validate AASHTO bearing stiffness specifications. Stiffness characteristics of the Florida Department of Transportation (FDOT) type bearing pads were theoretically determined under varying elastomer shear modulus values. FE models of AASHTO Type III and V girders were subjected to simulated static truck loads. Vertical and horizontal spring elements, simulating new bearing pads, were incorporated at the ends of the girder models. A full section of a bridge on U.S. Highway 27 was also modeled, and the results were compared with field tests. In general, the restraint effects of the bearing pads were beneficial to the performance of the girders and the bridge. The beneficial effect, however, was small for new bearing pads, and more pronounced under drastic increases in bearing stiffness because of aging and colder temperatures. Such dramatic increase in bearing stiffness may be considered in design. Current FDOT type bearing pads are serving the main purpose of their application, which is to provide vertical support with minimum horizontal restraint force to the girders, thus allowing horizontal movement and rotational movements.