Seismic Retrofit Optimization Strategy for Concrete Bridges Based on System-Level Performance

Abstract This paper presents a case study for evaluating different retrofitting strategies for reinforced concrete (RC) bridge columns aimed at enhancing the bridge system-level seismic performance under various damage states. It further explores a reverse retrofit design approach in which optimal schemes are derived by linking component-level retrofit strategies to the overall structural fragility. The optimization strategy involves evaluating the bridge seismic performance through incremental dynamic analysis, establishing performance limits, analyzing various column retrofitting configurations for effectiveness, and conducting fragility analysis to assess the probability of exceeding prescribed damage thresholds in the retrofitted bridge. The methodology is illustrated with a prototype bridge and two different column retrofits addressing different deficiencies. For the evaluated bridge, the results show that the column retrofit methods significantly improve the seismic performance of the bridge structure, particularly under minor damage states. Under the conditions examined, retrofitting three of four columns was slightly less effective than retrofitting all columns, although enhancing concrete and reinforcement strength could further improve outcomes in the minor and moderate damage states. These outcomes could be used to evaluate the postearthquake repairability and long-term maintenance costs associated with different retrofit strategies. Additionally, the effects of retrofitting configurations on bridge fragility depend on specific drift limits and spectral acceleration, with optimal configurations leading to significant reductions in failure probability, providing essential insights for performance-based retrofit designs with economic efficiency in mind.