REPLACEMENT DECISION OF CIVIL FACILITIES UNDER IMPERFECT MAINTENANCE

Abstract
Civil facilities require regular inspections and effective maintenance to ensure safe and uninterrupted operation throughout their service life. To analyze system reliability and optimize maintenance strategies, methods such as engineering reliability, Failure Mode Effects and Criticality Analysis (FMECA), and Fault Tree Analysis (FTA) are commonly used. Unlike manufacturing products, civil facilities experience failures rarely, making them rare events. For instance, a hydropower system in a Taiwanese reservoir reported only about 60 failures over 40 years, despite involving multiple subsystems like turbines, generators, and power transmission units. These low failure rates challenge traditional statistical methods, which often struggle with rare event modeling. Furthermore, facilities undergoing maintenance are typically not restored to a “like-new” state but to a “younger” one, reflecting imperfect maintenance. Over time, imperfect maintenance leads to gradual deterioration and rising costs. Since each facility operates under different environmental, material, and operational conditions, its reliability characteristics and degradation trends are unique. Moreover, along with imperfect maintenance progress, the facilities become more and more deteriorated and the maintenance costs increase incrementally. One of crucial decision after the long-term operation of the facilities is to determine maintenance or replacement in a cost-effective manner. As the occasion of the total maintenance cost over the replacement cost, the facilities should be replaced. Because the maintenance and replacement decision is a crucial and challenging task, many studies were conducted. As stated above, the civil facilities are under the process of continuous preventive maintenance and failure repair. However, their performance will generally accelerate to decline and the maintenance costs will increase along with time. Eventually, the economic service life of the civil facility under imperfect maintenance will be of importance to the maintenance management. How to make decision on the economic replacement time is the main focus of this paper. This study will adopt the concepts of replacement studies stated above, combined with the theories of reliability analysis, imperfect maintenance and engineering economics, to develop replacement decision model for the civil facilities under imperfect maintenance Keywords - Engineering Economics, Equivalent Uniform Annual Cost, Imperfect Maintenance, Reliability Analysis, Replacement and Maintenance, Weibull Distribution