Developmental Study on Structural Reliability Assessment Systems of Marine Structures

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1. At first, applicabilities of the program package developed for reliability assessment of marine structures are investigated through numerical examples for two typical semi-submersibles, which are modeled as spatial frames and subjected to quasi-static extreme loads based on ultimate strength analysis. Results obtained in this study are summarized as follows :(1) The underlying theory and the system's overview are provided. (2) The applicability of the system is demonstrated through the numerical examples for structures under beam and oblique seas (3) Effects of some design alterations on system reliability are also discussed by introducing importance factors as reliability measures under a damaged condition.2. Next, methods are presented for the probabilistic analysis on the ultimate strength and the natural frequencies of composite and slender offshore structures for deep water, which are treated as a simple tower model by replacing its tower frameworks and platform with the beam-columns with equivalent stiffness and strength, respectively. A method is also presented for reliability assessment of aged marine structures considering increase of extreme wave loads due to marine growth and corrosion, and deterioration of rigidity and resistance due to corrosion. Further, the effect of uncertainty on the natural frequencies is discussed by using a probabilistic sensitivity analysis method. Finally, the applicability of the proposed methods is demonstrated through the numerical example for a 450m guyed tower.