Deterioration Model for Establishing an Optimal Mix of Time-Based Maint. and Condition-Based Maint. for the Enclosure System

Buildings comprise hundreds of assets, such as roofs and boilers, each of which has different durability expectations and therefore requires a corresponding maintenance strategy to sustain their performance and function over their respective service lives. Maintenance strategies can be classed into those that are time-based (TbM) and those that are principally condition-based (CbM). Whereas the former group of maintenance activities is carried out on fixed intervals, consistently over the service life of an asset regardless of its age, the latter is dependent, in part, on the emergence of distress-metrics that are empirically measurable at different life stages. CbM contemplates age and exposure conditions, is variable in its intervals and conditional in its implementation. Many maintenance manuals have offered a rudimentary approach to enclosure assets that is heavily focused on TbM principles with minimal consideration of changes to the TbM ratios with the passage of time.

This paper argues that the ratio of TbM to CbM (that is, the maintenance mix) should be aligned to individual assets and also adjusted at different stages over their respective service lives. To this end, the paper advances a multivariate deterioration model to identify the key milestones along the life of an asset and offers principles for a maintenance mix to guard against the risks of under-maintenance and the lack of credibility that arises when owners perceive an overly conservative program of overmaintenance based upon simplistic considerations of fixed interval maintenance. The multivariate deterioration model reveals insights for a reliability-centred paradigm for maintenance of enclosure assets.

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