Next Generation Fragility Functions for Seismically Designed Highway Bridges in Moderate Seismic Zones

Despite the potential of high-consequence events, rarity of earthquake occurrences in moderate seismic zones and a misconstrued perception of risk has often led to a delayed onset of seismic detailing practices for highway bridges. While substantial literature exists on the development of seismic fragility curves for nonseismically designed highway bridges in these regions, additional efforts are required for vulnerability assessment of bridges with improved seismic detailing. Risk evaluation and preparedness of the transportation infrastructure to withstand damaging earthquakes requires seismic fragility estimation of bridges from both preseismic and postseismic design eras. Unlike past literature advocating traditional fragility curves for seismic vulnerability assessment, this study proposes parameterized fragility functions that offer multiple unique advantages. While incorporating the key aspects of seismic design detailing, these functions are conditioned on ground motion intensity as well as field measurable bridge-specific structural parameters. As a test bed, this study chooses the moderate seismic zone of central and southeastern US to develop parameterized fragility models for four prevalent seismically designed bridge classes using modern gradient-based least-square boosting algorithms. A statistical screening procedure helps prune a wide array of bridge parameters to the most critical ones that affect seismic response and fragility. Predicted fragility estimates using surrogate models show satisfactory match with benchmark Monte Carlo simulations rendering confidence in vulnerability predictions. Lastly, fragility comparisons between bridges with seismic and nonseismic detailing highlight the benefits of modern seismic design practices. The proposed fragility models are aimed to equip asset managers with tools for prompt fragility estimation and decision making.