Abstract
Probabilistic methods have been used in offshore structures for individual components and whole structures based on the ultimate strength of the structural components. A new method for the assessment of system failure using individual member probability of failure using the fault tree method has been developed and demonstrated using a typical offshore platform jacket. The logical sequences of the component failure have been assessed using the importance of member for local strength, attached joint requirement and the load path required to continue the load distribution in case the other members fail. The proposed method has been used to verify the probability of failure for an existing jacket designed using the Allowable Stress Design (ASD) method and the corresponding Reserve Strength Ratio (RSR) has been computed. The critical failure path has been generated and the probability of failure of the members involved in the established failure paths and corresponding RSR is evaluated by First Order Reliability Method (FORM). The system reliability analysis is then used to identify the combined probability of failure of the individual failure paths, which in turn results in the dominant failure path that leads to the collapse of the structure. Finally, the system failure is assessed using simple bound formula.
