Analytical and Field Investigation of Lateral Load Distribution in Concrete Slab-OnGirder Bridges

The objective of this paper is to evaluate the accuracy of equations specified by the current AASHTO LRFD codes for highway concrete slab-on-girder bridge bending moment distribution factors. A total of 645 bridges were modeled and analyzed using the three-dimensional finite element method. AASHTO HS20-44 design trucks were used in the analysis. The load distribution values obtained from analysis were compared to the code values. The results of this investigation indicate that the AASHTO LRFD load distribution equations for the interior girders of bridges with single-lane loading, as well as for the exterior girders of bridges with two or more design lanes loaded, are accurate for most practical cases. The accuracy of the code load distribution equations for interior girders of bridges for the latter loading case was found to vary with deck overhang, girder spacing, and span length. The relative error in this case ranged from 5 to 30% when compared with the finite element method. The limits of the overhang as specified by the LRFD Specifications were used in the analytical models. The results of the analysis also indicate that the relative errors caused by the use of the LRFD load distribution equation for the exterior girder for single-lane loading may vary significantly with deck overhang. For example, this variation ranges from -25 to 70% in this study. On the basis of this extensive investigation, three new equations are presented for the determination of load distribution factors of the interior girders of bridges having two or more lanes loaded and for the exterior girders of bridges with single-lane loading. Comparisons between seven bridge load tests and analytical results obtained from different theories show that the proposed equations are conservative and reasonably accurate. In addition, they are easy to use and provide a rational approach for strength evaluation and load rating of existing bridges.