AbstractAs the concept and methods of maintenance of infrastructure systems are receiving increasing attention, the optimal maintenance strategy for a group of structures is a promising research topic. Among the factors affecting the decision-making of optimal maintenance strategy for civil infrastructure systems, the target service life and user cost estimation approach are significant. Currently, user cost estimation at the project level is widely adopted, whereas the user cost estimation at the network level is in the development stage. This paper investigates the impact of several factors on the risk-informed optimal maintenance strategy for a bridge network under corrosion, including target service life, user cost estimation approach, and correlation among bridge safety margins. The novelty of this paper consists of considering the effects of these factors on the optimal maintenance strategy of bridge networks. These effects, which are crucial for adopting the optimal maintenance strategy, were not investigated in a detailed manner previously. Two different maintenance strategies are considered for the maintenance of corroded steel girders. The former is to conduct replacement with new carbon steel girders, and the latter is to use A709-50CR steel, where CR stands for corrosion resistant, a new type of steel with a chromium content similar to that of martensitic stainless steel, in replacement actions. Using an existing bridge network under a low life-cycle risk threshold, it is shown that replacement based on A709-50CR girders results in a reduced life-cycle network maintenance cost than replacement based on carbon steel girders. Also, the project-level approach to estimate user cost can lead to a substantial increase in the life-cycle network maintenance cost compared with the network-level approach.