Impact of LRFD Specifications on the Design of Texas Bridges

Project Description

This project evaluated the impact of adopting Load and Resistance Factor (LRFD) Bridge Design Specifications for typical prestressed concrete bridge girders. Researchers from the Texas Transportation Institute (TTI) worked with Texas Department of Transportation personnel to establish parameters for typical bridge girders. Detailed design examples were developed to illustrate calculations for bridge girders following both the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges (17th edition) and the AASHTO LRFD Bridge Design Specifications (3rd edition).

The researchers found that for Type C and AASHTO Type IV girders, LRFD specifications:

• have a relatively small impact on the flexural service load design;
• have a negligible effect on the maximum span length;
• increase the required transverse shear reinforcement area; and
• increase significantly the required interface shear reinforcement area.

The researchers also found for Texas U54 girders, LRFD specifications:

• have a small overall impact on flexural service load design;
• have a varied effect on the maximum span length, depending on support skew, strand diameter, and girder spacing;
• decrease the transverse shear reinforcement area values for all skews and both strand diameters; and
• increase significantly the interface shear reinforcement area.

The researchers verified that a transition to LRFD specifications would not significantly impact the flexural design requirements for typical prestressed concrete bridge girders in Texas. However, increased shear reinforcement requirements were addressed in part by the new interface shear provisions that were approved for the 2007 LRFD specifications.

Project Publications

Impact of LRFD Specifications on Design of Texas Bridges. Volume 1: Parametric Study 0-4751-1 (V1)

Impact of LRFD Specifications on the Design of Texas Bridges 0-4751-S

Impact of LRFD Specifications on Design of Texas Bridges. Volume 2: Prestressed Concrete Bridge Girder Design Examples 0-4751-1 (V2)

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