Computation of joint reliability importance of two gate events in a fault tree

Joint reliability importance (JRI) of two gate events (GEs) is investigated along with its properties in a fault tree (FT). Computation of JRI of two GEs involves complexity because statistical dependency between GEs exists as a result of replication of basic events (BEs). To avoid complexity in computing the JRI, the topological relationships of two GEs in a FT are identified and classified into three classes. The explicit formula for the JRI of the two GEs is derived. JRI for each class is shown to be computed by using a conventional FT algorithm. By illustrating min. cut set representation of the bridge network, it is also shown that the degree of relationship between two min. cut sets can be measured by the JRI of the corresponding two GEs.