This report presents a rating procedure for the load-carrying capacity evaluation of existing reinforced concrete bridges including T-beams, box beams, girder and slab bridges. The methodology was developed in the load and resistance factor format, which is very similar to the Load Factor Method in the current AASHTO Specifications. Realistic live loading parameters based on field measured truck loads and traffic volumes are used to classify the live load categories. In evaluating the structural strength, provisions are included to allow the variability in field inspection, maintenance efforts and deterioration in the rating process. Based on these load and strength parameters, partial safety factors are calibrated to a safety index of 2.8 using a database of 21 T-beam bridges and 15 slab bridges. Depending on the expected truck traffic loading and structural conditions, a bridge rating may now range from a level below the current inventory rating to a level higher than the operating rating. This new procedure allows for more subjective engineering judgments to be systematically and uniformly incorporated into the rating process. When structural conditions and/or traffic loadings are not readily available or unknown, lower and upper bounds may be established based on engineer's best judgments using the proposed procedures. This facilitates more reasonable decision making with respect to an overall bridge maintenance policy.
Abstract