Improving availability and cost performance for complex systems with preventive maintenance

This paper investigates improving system limiting availability and expected system cost rate for a complex system through age replacement preventive maintenance (PM). This study defines the complex system as a classic bridge reliability structure consisting of five independent subsystems. A competing risk model is used for each subsystem´s unique life distribution. This model includes two independent modes of failure for each subsystem. They assume the expected system failure repair time and PM action time are known or may be estimated. System-level age replacement PM models are developed for both system limiting availability and expected system cost rate. Often, both availability and cost performance are critical system characteristics. A methodology is presented that allows tradeoffs between availability and cost to be evaluated. The paper demonstrates the methodology for a specific example. The maintenance strategy assumes that failed subsystems are maintained according to their failure mode and working components are preventively maintained. This strategy applies whether failure maintenance or PM action is required. This strategy is selected, since, in terms of maintenance service, it lies between the extremes of pure system-level maintenance and independent subsystem-level maintenance. Limitations of the system-level maintenance strategy are identified