Three-dimensional nonlinear seismic performance evaluation of retrofit measures for typical steel girder bridges

Steel girder bridges are common bridges in North America which have exhibited considerable vulnerabilities in past earthquake events. This paper conducts nonlinear time history analysis using detailed three-dimensional models of typical multi-span simply supported and multi-span continuous steel girder bridges to evaluate the effectiveness of various retrofit strategies. Restrainer cables, steel jackets, shear keys, and elastomeric isolation bearings are assessed for their influence on the variability and peak longitudinal and transverse response of critical components in the bridges. The results indicate that different retrofit measures may be more effective for each class of bridges. For example, the restrainer cables are effective for the multi-span simply supported (MSSS) bridge, yet not the multi-span continuous (MSC) bridge; shear keys improve the transverse bearing response in the MSC bridge but are not effective in the MSSS bridge which exhibits less transverse vulnerability; and elastomeric bearings improve the response of the vulnerable columns in both the MSSS and MSC bridges yet lead to increased abutment demands in the MSC bridge. The study reveals that while a retrofit may have a positive influence on the targeted component, other critical components may be unaffected or negatively impacted. This lends support to vulnerability assessments that consider the impact of retrofit on system vulnerability reflecting the contribution of multiple components.