Evaluation of Seismic Risk Mitigation Techniques for RC Bridge Superstructure Vulnerable to Pounding

Observations from previous earthquakes worldwide have shown that existing bridges designed using outdated seismic standards are vulnerable to various damage modes, such as pounding and bearing displacement, highlighting the necessity of retrofitting. This study evaluates the effectiveness of different retrofit measures to upgrade the reinforced concrete bridge superstructure, namely steel dampers and rubber bumpers, aiming to reduce seismic demands and control movement. The numerical modeling approach of the selected retrofit systems is verified by comparing the hysteretic behavior with previous experimental results. The validated retrofit strategies are subsequently implemented on the three-dimensional model of a multi-span adjacent reference bridge commonly found in a medium seismicity region. Preliminary assessments performed on the existing and un-retrofitted bridge models indicated that the bridge superstructure's fundamental natural period of vibration is shortened due to the adopted retrofit measures. Fragility relationships are derived under various seismic scenarios to evaluate the seismic performance of the retrofit techniques through incremental dynamic analyses. The probabilistic assessment results indicate that the steel dampers effectively reduce bearing displacement demands, and rubber bumpers adequately decrease pounding force between adjacent bridges. This study thus helps select effective retrofit systems for upgrading the seismic performance of bridges vulnerable to different damage modes and mitigating their seismic risk.