Optimum maintenance of deteriorated steel bridges using corrosion resistant steel based on system reliability and life-cycle cost

Corrosion is a major deterioration mechanism of carbon steel bridges. Multiple maintenance actions have been proposed to meet the safety requirements for bridges subjected to corrosion, including preventive maintenance, such as repainting, and essential maintenance, such as girder replacement. Recently, corrosion-resistant steel has been adopted for bridge construction. However, a comprehensive comparison of different maintenance strategies is still an under-investigated research area, especially for the cost-effectiveness of using corrosion resistant steel to conduct essential maintenance. In this paper, a new type of corrosion-resistant steel, A709-50CR, is considered for girder replacement. Reliability- and risk-based bi-objective optimizations are conducted on a multi-girder carbon steel bridge to determine when and which carbon steel girders should be replaced under different target performance indicators. The objectives are to minimize the life-cycle failure probability/risk and the total life-cycle cost, including initial construction cost and life-cycle maintenance cost. Sensitivity analysis is performed on multiple factors associated with system reliability calculations, such as system models adopted and correlations among resistances of girders. The economic benefits of building an A709-50CR bridge and applying frequent repainting actions on a carbon steel bridge to avoid girder replacement are also investigated. The comparison of different construction and maintenance strategies for multi-girder steel bridges sheds light on their effectiveness.