System redundancy of bridges is studied by comparing load-carrying capacities between a bridge system and individual girders. Nonlinear 3D FE models of existing composite simple I-girder bridges and a non-composite continuous I-girder bridge, which were designed according to a previous design code, were developed to investigate the effect of bridge types on the system redundancy. A simple method is proposed to quantify system redundancy as a system factor for load rating. The proposed system factor facilitates accounting for the system redundancy into evaluating load-carrying capacity for existing bridges by using conventional linear elastic structural analyses.
