Evaluation of Live Load Distribution Factors for Aging Prestressed Concrete Bridges

Since the early 1950s when prestressed concrete (PSC) bridge design was first started, major changes to the design provisions have been made. This paper aims to evaluate the historical design provisions in terms of design capacities and load distribution. Seventeen existing bridges designed using the first PSC Criteria are evaluated. Additionally, a load test is performed on one sixty-year-old PSC I-girder bridge to help validate finite element models (FEM) developed for determining the load distribution factors. The verification of the model is conducted based on the results from the diagnostic load testing and the nondestructive tests. Since the load tests may not be at the governing location, the critical live load distribution factors are determined using the verified FEM by changing the transverse positions of trucks. The results of design capacity show that the overall performance of the flexural design is more consistent than that of the shear, and in some cases, the shear could be unsatisfactory. The same set of bridges are analyzed for the distribution factors using the FEM method, and the results are compared with the four historically available prediction models. The comparison shows that all four approaches provide reasonable estimation of the distribution factors, while the AASHTO Standard Specification underestimates the live load distribution for shear.