A new approach for robustness assessment of fixed offshore structures under imprecise marine corrosion

This paper presents a new approach for the robustness assessment of fixed offshore platforms under limited information. The effects of marine corrosion on the robustness of aging offshore structures is investigated. Due to scarce and imprecise information associated with the corrosion process, the amount of damage caused by the deterioration to the structural members cannot be specified precisely. Therefore, fuzzy variables are utilized to cater for the subjective character of the assessment of deterioration, which leads to an uncertain damage modeling. In this study, robustness refers to a high degree of independence between the uncertainty of the damage due to imprecise marine corrosion and the associated uncertainty in the structural safety. Robustness assessment based on an entropy measure is taken as the basis. While existing entropy-based robustness measures can provide a global view of structural robustness, the proposed methodology aims to scrutinize the structural robustness at various membership levels with respect to various degree of imprecision in uncertain damage. It is shown that this utilization of alpha-level discretization in the computation of an entropy-based robustness measure leads to improvements including a better correspondence with the intuitive understanding of uncertainty and robustness. The usefulness of the proposed method is demonstrated by way of investigations on fixed offshore platforms with different brace configurations.