Two alternative imperfect multiaction maintenance models

Systems such as civil structures (e.g. building and bridges) and man–machine–software (e.g. large servers and control systems) can be categorised into certain operational states with respect to the structural conditions. Different operational states result in different abilities to perform the given missions and different system failure rates. To improve the current operational states, a preventive maintenance (PM) action involving implementation of a recovery procedure for a system's hardware, software and operational environment (e.g. temperature and pressure) is needed. The above problem is captured in a multiaction maintenance model with imperfect maintenance caused by the number of PMs. The alternative imperfect multiaction maintenance models are proposed in this paper. One considers that the behavior with respect to the transition of states is not in order and the transition rate is independent of the number of PMs. The other supposes that the behavior of the state transition is in order and the transition rate depends upon the number of PMs. Based on such alternative models, the optimal PM periods and the optimal number of PMs before replacing/restructuring the overall system are obtained, which minimize the cost rate function over an infinite horizon.