Risk-Based Optimal Life-Cycle Maintenance Strategy for Bridge Networks Considering Stochastic User Equilibrium

The risk-based approach is a powerful tool to assess the impact of hazards on bridge networks. The results of risk analysis of a bridge network can be integrated into an optimization process to obtain the optimal maintenance strategy for the network under investigation. In the process of risk analysis, the time-variant probability of failure profile of each bridge in the network can be obtained through reliability analysis, while network analysis needs to be carried out to determine the failure consequences of each bridge. The deterministic user equilibrium approach, which assumes that each driver has the perfect information on the traffic status and will adopt the path that maximizes his/her own benefit, is widely adopted to calculate traffic flows on each link in the network. Given that the assumption behind the deterministic user equilibrium can be highly unrealistic, this paper adopts a stochastic user equilibrium approach to analyze the traffic flow on each link, thereby producing a more accurate estimation of failure consequences associated with bridge failure. The failure consequences associated with both deterministic user equilibrium and stochastic user equilibrium are used in the optimization process to determine the influence of user equilibrium calculation on the optimal maintenance strategy for a bridge network subjected to corrosion. In addition, A709-50CR, a corrosion-resistant steel, is adopted as a material for the new girders to replace the corroded carbon steel girders. Comparison is made on the optimal maintenance strategies associated with using A709-50CR and carbon steel for replacement. The results show that the user equilibrium calculation has a profound influence on the optimization results. In addition, A709-50CR is economically beneficial at achieving low life-cycle risk compared with carbon steel.