Structural reliability of offshore platforms considering fatigue damage and different failure scenarios

Abstract

Structural systems will normally fail as a consequence of a chain of different components failure es. In this paper, fatigue reliability of fixed offshore platforms is investigated by analyzing different failure scenarios. In order to evaluate the occurrence probability of a special scenario, it is divided into a finite number of sub-scenarios. All combinations of time sequences are generated for a given sequence of failures, using a specially developed program.In order to calculate the occurrence probability of each scenario, a massive reliability analysis should be done for each of corresponding sub-scenarios. A large number of sub-scenarios should be analyzed, therefore implementing time consuming traditional methods for evaluating fatigue reliability may be unrealistic, and a simplified and accurate method is required. Herein, an “Artificial transfer function” is used to calculate the cumulative fatigue degradation in components. The preciseness of the proposed method is evaluated using a numerical model, and then, it is used to calculate the occurrence probability of each sub-scenario. Based on the calculated values, probability of occurrence is obtained for each scenario, and finally, the failure probability of entire system is calculated. The proposed method can be used in inspection planning and evaluating the life extension of existing offshore platforms.