Optimization of life-cycle maintenance of deteriorating bridges with respect to expected annual system failure rate and expected cumulative cost

Civil infrastructure systems are subjected to progressive deterioration resulting from multiple mechanical and environmental stressors. This deterioration process is developed under uncertainties related to load effects, structural resistance, and inspection outcomes, among others. In this context, life-cycle optimization techniques provide a rational approach to manage these systems considering uncertainties as well as several budgetary and safety constraints. This paper proposes a novel optimization procedure for life-cycle inspection and maintenance planning of aging structures. In this procedure, the structural system effects are accounted for by modeling the structure as a series, parallel, or a series-parallel system whose components are subjected to time-dependent deterioration phenomena. Different possible repair options are considered depending on the damage state and the outcomes of each inspection. For each component, essential or preventive maintenance aiming at reducing the system failure rate, are performed when inspection results indicate that the prescribed threshold damage levels have been reached or violated. Otherwise, no repair is performed. Optimum inspection and maintenance plans are formulated by minimizing both the expected system failure rate and expected cumulative inspection and maintenance cost over the lifecycle of the structure. The proposed approach is applied to an existing bridge.