Flexural Design of High Strength Concrete Prestressed Bridge Girders - Review of Current Practice and Parametric Study

This is the third of four reports that document the findings of a Texas Department of Transportation sponsored project to evaluate the allowable stresses and resistance factors for high strength concrete (HSC) prestressed bridge girders. The second phase of this research study, which is documented in this volume, focused on three major objectives: (1) to determine the current state of practice for the design of HSC prestressed bridge girders, (2) to evaluate the controlling limit states for the design of HSC prestressed bridge girders and identify areas where some economy in design may be gained, and (3) to conduct a preliminary assessment of the impact of raising critical flexural design criteria with an objective of increasing the economy and potential span length of HSC prestressed girders.The first objective was accomplished through a literature search and survey. The literature search included review of design criteria for both the American Association of State and Highway Transportation Officials (AASHTO) Standard and Load and Resistance Factor Design (LRFD) Specifications. Review of relevant case studies of the performance of HSC prestressed bridge girders as well as important design parameters for HSC were carried out. In addition, researchers conducted a survey to gather information and document critical aspects of current design practices for HSC prestressed bridges. The second objective was accomplished by conducting a parametric study for single-span HSC prestressed bridge girders to primarily investigate the controlling flexural limit states for both the AASHTO Standard and LRFD Specifications. AASHTO Type IV and Texas U54 girder sections were considered. The effects of changes in concrete strength, strand diameter, girder spacing, and span length were evaluated. Based on the results from the parametric study, the limiting design criteria for HSC prestressed U54 and Type IV girders using both the AASHTO Standard and LRFD Specifications for Highway Bridges were evaluated. Critical areas where some economy in design may be gained were identified. The third research objective was accomplished by evaluating the impact of raising the allowable tensile stress for service conditions. The stress limit selected for further study was based on the current limit for uncracked sections provided by the American Concrete Institute (ACI) 318-02 building code and the limit used for a specific case study bridge in Texas. Recommendations for improving some critical areas of current bridge designs and for increasing bridge span lengths are given.