リスク評価に基づく船体縦曲げ最終強度の目標安全性の検討

概要

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In this study, the target reliability level of ships ultimate hull girder strength is investigated by employing risk assessment. The risk can be defined as "Risk = Failure probability x Consequence." In the present case, the failure probability corresponds to the probability of hull girder collapse in bending while the consequence to a monetary loss accompanied by the failure. First, a risk model for the hull girder collapse and the limit state function are set up. Uncertainty models for the various parameters in the limit state function for the hull girder collapse are investigated. Among them are the yielding stress, plate thickness, corrosion, wave randomness, nonlinearity of wave loads, and so on. A series of reliability analysis is performed to obtain the relation between the safety level and deck plate thickness as a risk control option. Then, the target reliability level is investigated through Cost Benefit Analysis (CBA). It is shown that the obtained target reliability level is close to the reliability level of the existing ships whose design complies with the current Common Structural Rules. Finally, a sensitivity study is conducted to investigate into the impact of the risk model parameters to the target safety levels. It is discussed how different views may affect the target safety levels.