A time-dependent system reliability and lifecycle optimization framework for RC structures subjected to bidirectional corner-rebar corrosion: Seismic fragility, energy-based functionality loss, and optimal maintenance

The spatial non-uniformity of chloride-induced corrosion in RC structures causes combined pitting and uniform corrosion, challenging traditional corrosion models that treat these modes separately. This study develops a time-dependent system reliability framework to assess pre-earthquake initial functionality and lifecycle seismic fragility of corroded RC structures. A corrosion model distinguishing corner (CR-PCUC) and non-corner (NCR-PCUC) reinforcement is embedded into a corrosion-dependent damage limit state (DLS) model. Time-dependent seismic fragility analysis is performed based on the degraded DLS. A novel energy-based functionality loss model linking hysteretic energy, corrosion level, and residual functionality is proposed to quantify system performance degradation over time. Chloride removal maintenance is incorporated to mitigate functionality loss and enhance resilience. A bi-objective lifecycle optimization framework minimizes maintenance cost and functionality loss under budget and weight constraints. Results show corner reinforcement corrosion is more severe than non-corner; DLS decreases with corrosion duration. Initial functionality drops from 1.0 to 0.35 (CR-PCUC) and 0.38 (NCR-PCUC); collapse fragility increases from 1.3% to 22.0% (CR-PCUC) and 18.8% (NCR-PCUC). The proposed framework demonstrates that larger maintenance budgets improve both resilience and functionality, providing a quantitative decision support tool for balancing pre-disaster resilience and lifecycle costs under uncertainty.