Optimization of reinforcement strategies for dangerous dams considering time-average system failure probability and benefit-cost ratio using a life quality index

Lifetime-oriented multi-objective optimization for structural reinforcement based on series-system reliability and benefit-cost analysis has already been proposed. It is still needed, however, to incorporate the life quality index (LQI) in the lifetime reinforcement optimization process of complex massive infrastructure engineering with correlated series-parallel failure modes (e.g., dams). An improved technique combining overall system failure probability with benefit-cost analysis based on the LQI is developed. An approach to obtain time-average system failure probability with correlated series-parallel failure modes is proposed to measure the structural performance. Then, the concept for benefit-cost ratio based on LQI including failure consequence and life quality objective is introduced. As an application of the methodology, the optimal reinforcement strategy for an existing earth dam is shown. Three types of reinforcement strategies, that is, preventive reinforcement, essential reinforcement and that lies between them, are selected. The results show that the preventive reinforcement strategy is the most beneficial for a dam, whose failure loss involving human life is tremendous. The advantage of the proposed approach is its ability to harmonize overall structural safety with reinforcement cost and can be extended to optimization of reinforcement strategies for other massive infrastructure engineering projects.