Comparison of Measured and AASHTO LRFD-Predicted Residual Prestress Forces, Shear and Flexural Capacities of High-Strength Prestressed-Concrete Bridge Girders

Abstract

This paper describes a case study to quantify the behavior of precast, prestressed-concrete bridge girders made with high-strength concrete. As part of the case study, four bridge girders made with 77.2-MPa (11.2-ksi) concrete were salvaged from a decommissioned bridge in Orem, Utah. Each girder was subjected to a flexural cracking test to determine a prestress loss of 22% after approximately 7 years of service life. Once the prestress losses were quantified, a flexural capacity test was performed on one girder. Shear capacity tests were performed at various distances from the support on the remaining three girders. The measured prestress losses and various capacities were compared with estimated values calculated according to procedures in current bridge specifications. The predicted flexural capacity was found to be 7.3% conservative compared with the measured capacity. The measured shear capacities were all within 12% conservative compared with the AASHTO shear procedures. In addition to the physical tests, a nonlinear finite-element analysis was conducted and was found to replicate the experimental behavior, failure mechanism, and magnitude.