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This report investigates a new methodology for load rating of older reinforced concrete flat-slab and T-beam bridges in Indiana, using the tools of 3D finite element analysis. The Conventional Load Rating (CLR) method currently in use by INDOT relies on a simplified 2D analysis based on beam theory that may underestimate bridge capacity. Since the actual behavior of a bridge structure is 3D in nature, a 3D computational model is better suited to estimate bridge response for load rating. 3D finite elements models are capable of reflecting actual bridge dimensions, cross sections, and connection configurations. More importantly, with three-dimensional models, the load distribution in the transverse direction of the deck can be explicitly represented, and therefore optimized for maximum impact on load rating. Using 3D models, it is also possible to account for support continuity, variable cross sections, skew factor, edge railings, and other parameters that impact bridge behavior. It is therefore expected that load rating using 3D analysis can result in a more accurate assessment of bridge load carrying capacity compared to CLR by improving demand estimates. A sample of ten representative bridges (five of each type) is selected for this study. The representative bridges were identified based on the statistical distribution of older flat slab and T-beam RC bridges in Indiana. Load rating analysis results for the sample bridges using 3D analysis were compared to ratings obtained using CLR to identify factors contributing to bridge capacity that are not accurately represented with current rating standards. The results show significantly improved rating factors using 3D FE models. A sensitivity study was conducted to assess the impact of select parameters on load rating results and identify potential improvements to current load rating procedures using CLR. |
