| In today's society, most real-world systems exhibit multiple paths to failure. Yet only the likelihoods of failure associated with the occurrence of these failure paths have been analyzed. Thus, in order to effectively manage the risk associated with systems, both the likelihoods of failure and the consequences of multiple failure paths should be considered. Therefore, this research effort develops a methodological framework for evaluating risk from the perspective of compound failure modes. Compound failure modes are defined as two or more paths to failure with consequences that depend on the occurrence of combinations of failure paths. Furthermore, knowledge of the joint probability distribution of the occurrences of the failure paths and their consequences is important.; The methodological framework consists of the integration of the following four elements: (1) identification of compound failure modes, (2) quantification of the unreliabilities, (3) quantification of the risk, and (4) multiobjective tradeoff analysis of risk management options. A hierarchical holographic modeling (HHM) framework is used to identify compound failure modes. The unreliabilities associated with these failure modes occurring in combination are analyzed using fault tree models and time-to-failure models. Using risk of extreme events analysis and statistics of extremes, the unreliabilities from such models, along with the consequences, are evaluated to quantify the risk associated with the compound failure modes. Finally, a multiobjective tradeoff analysis, using multiple design options for the failure modes, is conducted through the surrogate worth tradeoff (SWT) method.; As a demonstration, the risk of compound failure modes in automated highway systems (AHS) is addressed. The many paths to failure in automated highways include: collision-avoidance, intelligent cruise control, lateral guidance, entry lanes, ice detection, and incident management Systems. The failure of any of these subsystems will cause the failure of the AHS. Different consequences are associated with each of these subsystem's failing. By analyzing the probabilities of failure and consequences associated with compound failure modes, a fuller perspective of the risk associated with the AHS failure modes is obtained. Cost versus risk tradeoff analyses are conducted to manage the risks associated with these failure modes. |
