Determining Prestress Losses, Residual Capacity, and Degradation from Testing of Prestressed Concrete Bridge Girders after 56 Years of Service

Prestressed concrete bridges built as early as the 1950s and still in use have deteriorated as a result of prestress losses, aging, and corrosion. This deterioration necessitates load posting, repair, retrofit, or deconstruction of bridge structures. Accurately estimating prestress losses as a part of the condition assessment of an in-service aging girder is a critical factor in determining the safe remaining service life, or in designing an intervention to extend that service life. This paper investigates the long-term prestress losses, residual girder capacity, and effect of deterioration on the structural response of four prestressed concrete bridge girders, recovered from the Herbert C. Bonner Bridge in North Carolina, United States, after 56 years in service. The full-scale AASHTO Type III girders were tested to failure to evaluate the total amount of prestress loss each girder experienced, and the performance of girders with and without visibly corroded strands. The experimental results are compared to several analytical prestress loss calculation methods provided in the AASHTO LRFD code and the AASHTO Standard Specifications. Sectional analysis models of the girders were also developed in the software program Response. The results indicate that corrosion of strands can significantly influence prestress loss, and that models developed in Response can capture these effects by accounting for the lost cross-sectional area of corroded strands. The research recommends the use of Response to model the behavior of aged prestressed concrete girders. A comparison of the predicted prestress losses to the experimental results shows that in situ material properties can effectively be used near the end of the service life to accurately estimate prestress losses. The study also recommends that the design life of prestressed concrete bridge girders could be safely extended by relaxing the zero tensile stress limits under service conditions that some transportation authorities adopt, even if only near the end of service.