Bayesian Reliability Analysis and Inspection of Ship Structural Members : An Application to the Fatigue Failures of Hold Frames

A Bayesian reliability analysis on fatigue strength of ship structural members is made to determine an appropriate inspection interval based on the results of periodical inspections which maintains the reliability of ship structure at a certain level equal to that initially expected at design stage. A general formulation is proposed for the case where the history of inspection and repair is given under the following assumptions that (1) fatigue life of the structural member considered follows a two-parameter Weibull distribution, (2) its scale parameter is unknown and (3) the uncertainty of inspection is introduced in terms of the average detectability which is determined from the probability distribution of fatigue crack size and the detectability of certain size of a crack. From the results of numerical analysis of inspection records on fatigue crack damages of hold frames of a ship, it is found that the estimated number of cracked members was close to that detected by the successive periodical inspections. It is thus concluded that, by performing similar analysis on other structural members of ships, the present method would be useful for determining appropriate inspection interval based on the evaluation of the safety of ship structure.