This report describes a methodology for demand estimate through the improvement of load distribution factors in reinforced concrete flat-slab and T-beam bridges. The proposed distribution factors are supported on three-dimensional (3D) Finite Element (FE) analysis tools. The Conventional Load Rating (CLR) method currently in use by INDOT relies on a two-dimensional (2D) analysis based on beam theory. This approach may overestimate bridge demand as the result of neglecting the presence of parapets and sidewalks present in these bridges. The 3D behavior of a bridge and its response could be better modeled through a 3D computational model by including the participation of all elements. This research aims to investigate the potential effect of railings, parapets, sidewalks, and end-diaphragms on demand evaluation for purposes of rating reinforced concrete flat-slab and T-beam bridges using 3D finite element analysis.

The project goal is to improve the current lateral load distribution factor by addressing the limitations resulting from the 2D analysis and ignoring the contribution of non-structural components. Through a parametric study of the slab and T-beam bridges in Indiana, the impact of selected parameters on demand estimates was estimated, and modifications to the current load distribution factors in AASHTO were proposed.

Report Number



reinforced concrete bridge, live load distribution factor, finite element analysis, non-structural elements, modification factor

SPR Number


Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, IN

Date of this Version