Impact of LRFD Specifications on the Design of Texas Bridges

This project summary report summarizes the research performed in Texas Department of Transportation (TxDOT) Project 0-4751. TxDOT has historically designed highway bridge structures using the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges. However, the agency is in the process of transitioning to the use of the AASHTO Load and Resistance Factor (LRFD) Bridge Design Specifications. This two-year project aimed at determining whether the LRFD Specifications result in significant changes in the design of typical Texas bridges as compared to the Standard Specifications. The project focused on typical Texas prestressed concrete bridge girders because of the prevalence of these elements in standard TxDOT bridge designs. Researchers worked with TxDOT personnel to establish parameters for typical bridge girders. Detailed design examples were developed to illustrate the design calculations for bridge girders following both the LRFD Specifications and the Standard Specifications. A parametric study was conducted for several girder types. TTI researchers verified that the flexural design requirements for typical prestressed concrete bridge girders in Texas are not significantly impacted by a transition from the Standard Specifications to the LRFD Specifications. However, changes in the provisions for transverse and interface shear design have led to increased shear reinforcement requirements. This increase is addressed in part by the new interface shear provisions that have been approved for the 2007 LRFD Specifications.