Energy-based fragility assessment of reinforced concrete bridges considering cumulative seismic demand under mainshock-aftershock sequences

Abstract

Bridges in high-intensity seismic zones are particularly vulnerable to sequential seismic events, yet conventional performance assessments often consider only mainshock (MS) effects, overlooking the influence of aftershocks. To address this limitation, this study systematically investigates the seismic energy distribution in I-girder multi-span reinforced concrete (RC) bridges subjected to both mainshock-only and mainshock-aftershock (MSAS) sequences. A dataset comprising 269 real MSAS seismic records is employed to evaluate cumulative seismic energy demands and dissipation mechanisms across key bridge components, enabling a more comprehensive assessment of structural performance. Results indicate that aftershocks significantly increase total energy accumulation, with MSAS sequences causing greater hysteretic and damping energy dissipation than MS-only cases. Bearings are identified as the primary energy-dissipating components, critically influencing overall seismic response. Unlike deformation-based parameters, energy-based metrics consistently increase with aftershock inclusion, making them more reliable for quantifying seismic demand. To facilitate energy-based fragility analysis for components and bridge systems, equivalent energy-based limit states are established through statistical correlations with traditional deformation-based parameters. The resulting fragility functions demonstrate that energy-based demand parameters effectively capture cumulative structural behavior throughout the seismic sequence. These findings enhance understanding of seismic energy quantification, enable the translation of classical deformation-based metrics into energy-based parameters, and support more unified and resilient performance evaluation strategies for bridges in regions exposed to sequential seismic hazards.