Fatigue Life Estimation of Offshore Structures Under Variable Loads.

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This research project consists of two topics. In the first topic titled "Fatigue Test Using Multi-Notched Specimen and Its Reliablilty Analysis", a fatigue testing method using a multi-notched test specimen are presented for the purpose of estimating the distribution function of fatigue crack initiation life by a small number of fatigue tests. Emphasis is put on the effective use of the fatigue data provided by one test specimen and to decrease the number of specimens required in the fatigue tests. The experimental results indicate that two or three multi-notched specimens are enough to determine the distribution function of crack initiation life of practical level.In the second topic titled "Effect of In-Service Inspection on the Reliability Degradation of Structrues Due to Fatigue Damage", a general method for estimating the reliability of structural member through periodic in-service inspections is developed. Choosing a connecting component of TLP tendon, which has a possibility of failure before and after the fatigue crack initiation, reliability analysis of inspections are carried out. And the effects of fatigue properties of member, the failure rate of member, detectability of a crack by inspection and the shape of initiated crack on the structural reliabilities are discussed.