ABSTRACT

Sensitivity analysis on fatigue reliability and inspection is carried out for a typical structural member of bulk carrier. Fatigue properties of the member and probability of crack detection at the field inspection are obtained by the questionnaire asked to the naval engineers. Changing stress level(fatigue life) of the member, crack growth curve and inspection interval as parameters around a standard condition, failure probabilities of member during 20 years" service are calculated by the Markov chain model. The result of analysis can suggest the solutions for design requirements such as improvement of reliability level, reduction of structural weight and the simplification of inspection. In the latter part of the paper, effectiveness of combined inspection method and sampling inspection method are discussed through the sensitivity analysis assuming member sets having different number of initiated cracks. It is found that combined inspection has more advantage than sampling inspection, when the number of members having initiated crack is a few in the inspecting member set.

1. INTRODUCTION

In-service inspection on ship structure plays an important role for maintaining safety against fatigue damage. However, when we want to perform reasonable inspection, it is necessary to clarify the present reliability level of structural members as well as the desirable level. From this point of view, in the previous study, we conducted questionnaire about "Fatigue damage and inspection of bulk carrier" to naval engineers(Fujimoto et al, 1996, Kim et al, 1996 and SR226 Committee, 1996). In the questionnaire, six locations of bulk carrier reporting frequent damage occurrences were selected and the number of cracks initiated in the members, the fatigue characteristics of members, the probability of crack detection by field inspection, the target reliability level of members, etc., were asked.

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