IMPROVED LIVE LOAD DISTRIBUTION FACTORS FOR USE IN LOAD RATING OF SLAB AND T-BEAM REINFORCED CONCRETE BRIDGES

This study aimed to investigate potential improvements in load estimation in the standard load rating procedure of reinforced concrete slab and girder bridges. Three-Dimensional (3D) Finite Element (FE) models were used to conduct refined analyses of bridges using full-scale models that account for non-structural elements in superstructure modeling. The rating results obtained from FE analysis for a small sample of bridges indicated that Conventional Load Rating (CLR) methodology could lead to conservative rating factors mainly due to demand overestimation. A parametric study associated with demand assessment showed a substantial impact of geometric features on bridge moment and shear values. The study showed that edge-elements such as railings and end-diaphragms significantly changed the distribution of loads over the bridge width due to the edge-stiffening effect.

Effects from the presence of edge components are not reflected in the methodology outlined in American Association of State Highway and Transportation Officials (AASHTO) specifications and may be a source of overestimation or underestimation of demands on bridges. Potential improvements to current live load Distribution Factor (DF) formulations were identified based on statistical studies where bridge responses subjected to standard truck load configurations obtained from FE analysis were compared to the current procedure’s corresponding results. Modification Factors (MF) to live load DF were proposed to incorporate secondary elements’ effect in demand estimates. Updated DFs could result in more accurate rating factors when used in the CLR of existing slab and T-beam bridges. This would benefit a great population of bridges conservatively rated as structurally deficient. The proposed modifications could prevent unnecessary rerouting, weight posting, bridge closure, and replacement.