AbstractCompared to linear analysis approaches, nonlinear analysis of bridge models under large seismic demands has enabled more realistic prediction of global and local responses. However, the sensitivity to modeling assumptions, element and material formulations, software-dependent implementations, and parameter selection may lead to variable results between nonlinear analysis software packages. While previous work has led to a better understanding of how to model nonlinear static response of bridge components and systems, seismic loads and the corresponding material hysteresis introduce additional sources of variability in the nonlinear response. Two ordinary standard bridges in California were analyzed using simplified steel and concrete constitutive models in concentrated plasticity elements for the columns and nonlinear gap-link springs for the abutments. The models were implemented in SAP2000 and OpenSees and calibrated to achieve common material, section, and element-level nonlinear static responses. Subsequently, the models were extended to seismic excitation with common unloading-reloading rules for the material models as well as common definitions for damping and mass. Analysis results showed consistent drift, base shear, and moment-curvature response histories between the software packages. However, the nonlinear seismic response sensitivity for alternative column hinge formulations and abutment models should be investigated in future studies.