Impact of LRFD Specifications on Design of Texas Bridges. Volume 1: Parametric Study

The Texas Department of Transportation (TxDOT) is currently designing highway bridge structures using the American Association of State Highway and Transportation Offrcials (AASHTO) Standard Specifications for Highway Bridges, and it is expected that the agency will transition to the use of the AASHTO LRFD Bridge Design Specifi.cations before 2007. This is a two-volume report that documents the findings of a TxDOT sponsored research project to evaluate the impact of the Load and ResistanceF actor (LRFD) Specifications on the design of typical Texas bridges as compared to the Standard Specifications. The objectives of this portion of the project are to evaluate the current LRFD Specifications to assess the calibration of the code with respect to typical Texas prestessed bridge girders, to perform a critical review of the major changes when transitioning to LRFD design, and to recommend guidelines to assist TXDOT in implementing the LRFD Specifications. A paramehic study for AASHTO Type IV, Type C, and Texas U54 girders was conducted using span length, girder spacing, and strand diameter as the major parameters that are varied. Based on the results obtained from the parametric study, two critical areas were identified where significant changes in design results were observed when comparing Standard and LRFD designs. The critical areas are the transverse shear requirements and interface shear requirements, and these are further investigated. In addition, limitations in the LRFD Specifrcations, such as those for the percentage of debonded strands and use of the LRFD live load distribution factor formulas, were identified as restrictions that would impact TxDOT bridge girder designs, and these issues are further assessed. The results of the parametric study, along with critical design issues that were identified and related recommendations, are summarized in Volume I of this report. Detailed design examples for an AASHTO Type IV girder and a Texas U54 girder using both the AASHTO Standard Specifications and AASHTO LRFD Specifications were also developed and compared. Volume 2 of this reoort contains these examples.