Life-Cycle Seismic Loss Assessment of Aging Infrastructure Subjected to Multiple Mainshock-Aftershock Sequences and Long-Term Environmental Exposure

Probabilistic risk assessments provide a valuable basis for managing the safety and functionality of infrastructure exposed to extreme hazards, where the economic loss is increasingly recognized as a critical performance metric. In seismically active regions, infrastructure systems are frequently subjected to mainshock-aftershock sequences, while long-term environmental exposure further exacerbates their vulnerability to seismic events. However, existing frameworks have limited capability to estimate the economic loss of aging infrastructure under multi-hazard conditions. This study proposes a life-cycle seismic loss assessment framework for aging infrastructure under coupled mainshock-aftershock and environmental deterioration effects. In this framework, a hierarchical Markov process is employed to describe the structural state evolution induced by multiple stochastic seismic sequences and long-term aging effects. Furthermore, time- and state-dependent fragility surfaces are developed to capture the evolving structural capacity under multiple hazard mechanisms, explicitly representing the coupled effects of sequential seismic loading and long-term environmental deterioration. Finally, a new generalized recovery model is formulated to provide a unified and flexible representation of recovery processes under various resource constraints and repair strategies, enabling a more realistic characterization of partial performance restoration due to incomplete repair actions. A case study on an aging containment structure is conducted to demonstrate the applicability of the proposed Markovian framework. The results show that the consideration of multi-hazard-induced damage accumulation and incomplete repairs substantially increases the expected seismic loss, highlighting the necessity of incorporating multi-mechanism damage evolution when evaluating the long-term seismic risk of aging infrastructure.