Nonlinear Fragility Analysis of Three Different Concrete Bridge Mid-Column Structural Types

Reinforced concrete (RC) road bridges play a crucial role in transportation infrastructure and must endure varying degrees of damage during seismic events, including the risk of collapse. Their resilience is vital for post-earthquake recovery, enabling the movement of emergency services and goods. While some bridges may require repairs, many can still accommodate emergency vehicles. This study focuses on the seismic assessment of bridges, particularly those built under outdated regulations, guided by European standards such as EN 1998. This paper presents a comparative numerical analysis of three bridge models with identical superstructures but varying substructures, specifically the mid-columns. The analyzed prestressed concrete bridges span 88 meters and adhere to European standards. By employing nonlinear analysis methods, the study assesses how design variations influence seismic fragility and column responses. Key findings reveal that design choices significantly affect structural performance, highlighting the need for rigorous seismic evaluations. Fragility curves indicate that Model 1, despite strong initial resilience, exhibits increased vulnerability under severe conditions. In contrast, Models 2 and 3 demonstrate enhanced resilience, especially in extensive and complete damage states. This analysis emphasizes the importance of ductility in bridge design, with Model 2 proving particularly effective for regions prone to high seismic activity. Overall, the study underscores the necessity for continuous optimization of bridge designs to mitigate seismic risks and ensure safety and functionality during and after earthquakes.