A methodology is proposed to analyze the structural redundancy of bridge systems under lateral loads. The paper compares the results obtained from a probabilistic approach to those of a simplified deterministic analysis. A non-linear finite element analysis based on a 3-D frame model is performed for an example bridge considered to be representative of the behavior of structures with integral column-superstructure connections. The analysis accounts for material non-linearity using realistic models for the stress-strain relationships of the different constituents. The quantification of the available redundancy levels is evaluated using reliability as well as deterministic criteria previously proposed in NCHRP 458.