Comparison of load rating of reinforced concrete slab bridge using analytical and field testing approaches

Bridge load rating using field testing often results in greater load capacities compared to the analytical approaches specified in the American Association of State Highway and Transportation Officials (AASHTO) standards. This paper presents a load rating evaluation of a 96-year-old skewed RC slab bridge using analytical and field testing approaches to determine how field tests influence the load rating for the bridge. The bridge is subjected to two types of load tests: diagnostic load test under a single lane load (SLL) and proof load test under a multilane load (MLL). Using the test results, the bridge is load rated using AASHTO’s Manual for Bridge Evaluation approaches and the structural effective strip width approach to compare with the analytical rating factor (RF) computed using AASHTO’s beam-line model. Additionally, the beam-line model for the bridge is calibrated using the SLL diagnostic test results to determine a modified RF for the controlling MLL case. Furthermore, to explore the potential of using image-based displacement measurement methods in bridge load testing, in addition to using conventional sensors, a cellphone camera and a feature-based image registration (FBIR) technique are utilized to measure the bridge displacements. The results of the study show that the modified RFs computed for the controlling load case are as much as 26% below the analytical load rating, indicating that load testing may result in reduced RFs for some RC slab bridges. Displacements obtained using the FBIR method show close agreement with that obtained using conventional displacement sensors.