Simplified method for estimating restraint moment induced by vertical temperature gradient in continuous prestressed concrete bridges and verification using AASHTO BDS

Abstract

Diurnal and seasonal temperature variations cause uniform temperature changes, vertical temperature gradients, and horizontal temperature gradients. Vertical temperature gradients occur when the bridge deck absorbs heat due to solar radiation more than the bottom parts of bridge girders. Consequently, the vertical temperature gradient causes redistribution of bearing reactions, and induces additional flexural stresses in continuous spans. Estimating the vertical temperature gradient effect on continuous concrete bridges requires knowledge of thermal analysis of statically indeterminate structures or advanced three-dimensional (3 D) finite element (FE) analysis. Therefore, this article focuses on developing a simplified analysis method for estimating vertical temperature variations effects on continuous prestressed concrete bridge girders, which is required for bridge design. Restraint moments induced by vertical temperature gradients are investigated using 3 D FE analysis. A total of 115 bridges with different configurations (number of spans, girder spacing, and girder type) were analyzed to estimate the positive thermal moments at support locations. Results from these analyses were then used to develop simplified equations for estimating the positive restraint moments due to vertical temperature gradients from AASHTO LRFD Bridge Design Specifications (BDS). The developed equations are validated using John James Audubon Bridge #2 field data, and for other AASHTO LRFD temperature zones.