Seismic retrofit of steel bridges requires more advanced analysis techniques to determine capacities and predict inelastic performance parameters. Normal engineering analysis practice assumes linear-elastic behavior for structural members, which fails to reliably account for re-distribution of forces due to member non-linear behavior and dissipation of energy due to material yielding. The performance criteria for the 1958 Carquinez Strait Bridges is “no-collapse” which implies that structural members may yield, exhibiting both material and geometric nonlinear behavior, provided that sufficient reserve strength and ductility remains to prevent the structure from collapsing. With increasing construction costs and tighter budgets, a key component in removing overconservatism in the final retrofit design and effecting a cost-efficient, yet sound design solution, is to take a more rigorous approach to the structural analysis. Advances in technology for computer hardware and software permitted the 1958 Carquinez Strait Bridge seismic retrofit project team to perform a non-linear dynamic analysis for the main span structure in order to better characterize the behavior of the bridge and quantify the damage the structure might sustain during a large seismic event. This paper discusses the non-linear pushover analysis, which was a key component of the non-linear dynamic analysis and of the overall retrofit design effort for the bridge. The development of the material properties for the steel members is discussed and results of the as-built, prototype retrofit and final retrofit pushover analyses for one of the bridge towers is used to examine the procedures and rationale implemented to perform a performance based analysis and design