Lifetime reliability-based optimization of post-tensioned box-girder bridges

This paper presents a lifetime reliability-based approach for the optimization of post-tensioned concrete box-girder bridges under corrosion attack. The proposed approach is illustrated by determining the optimal life-cycle cost and CO2 emissions of several initial designs of post-tensioned box-girder bridges with different objectives, i.e. the lowest initial costs, the longest corrosion initiation time, or the maximum safety. The study was conducted in two steps. Firstly, the Pareto set presents initial designs considering the cross-section geometry, the concrete strength, the reinforcing steel and the prestressing steel. Secondly, the maintenance optimization was conducted with the proposed method, aimed at minimizing the economic, environmental and societal impacts of the bridge while satisfying the reliability target during its life-span. Effective maintenance is able to extend the service life of the bridge with the minimum cost and CO2 emissions. It is indicated that a durability-conscious initial design is particularly beneficial for life-cycle performance. Besides, the emphasis on the initial design can also have an effect on the life-cycle performance of bridges. It is found that designs with longer corrosion initiation time are associated with lower life-cycle cost, especially when using concrete of higher strength. Findings from the current paper also indicate that optimal maintenance strategies are more likely to be those with fewer maintenance actions that repair all deteriorating structures simultaneously.