Reliability Improvement Allocation Method Considering Common Cause Failures

In this article, common cause failure, which has contributed more and more failures of complex systems, is integrated to the reliability allocation process. Factors that are used to weight the components are proposed as failure severity, improvement effort, coupling strength, and fragility. Failure severity in the context of common cause failure (CCF) is calculated based on the component's expected marginal contribution to different common cause component groups. The alpha factor model is employed to generalize the reliability improvement effort for CCF. Mathematical formulation for calculating the coupling strength is developed to explore how the CCF affects the factors. A reliability improvement rate is developed to achieve a valid reliability improvement for each component. This kind of allocation considers the component reachability for a given reliability improvement target. Application frameworks of the proposed method to series and parallel systems are constructed. Two illustrative examples are presented to demonstrate that the proposed approach is more effective for proportionally assigning the system reliability requirements in the context of CCF.