Validation of AASHTO Bearing Stiffness for Standard Precast Concrete Bridge Girders

Precast AASHTO concrete bridge girders are often supported at the ends by 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) model-ing was used to validate AASHTO bearing stiffness specifications. Stiffness characteristics of the Florida Department of Transportation (FDOT) type bearing pads were theoretically deter-mined under varying elastomer shear modulus values. Finite ele-ment models of AASHTO Type III and V girders were subjected to simulated static truck loads. Vertical and horizontal spring ele-ments, 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 compared with field tests. In gen-eral, the restraint effects of the bearing pads are beneficial to the per-formance of the girders and the bridge. The beneficial effect, how-ever, is small for new bearing pads, and more pronounced under drastic increases in bearing stiffness due to aging and colder tem-peratures. Such dramatic increase in bearing stiffness may be con-sidered in design. Current FDOT type bearing pads are serving the main purpose of their application, which is to provide vertical sup-port with minimum horizontal restraint force to the girders, thus allowing horizontal movement and rotational movements.