Phase III maintenance strategies

The map below displays, for all countries for which data is available, the phase III maintenance strategies utilised. A table view of the same data is available at the bottom of this page

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Phase III: Assessment and prediction by advanced analysis (Structural Health Monitoring (SHM) and Modelling)

For problems with substantial consequences, an advanced analysis for performance assessment and performance prediction should be planned to carefully check the proposal for the pending decision that results from phase I and II. In assessing an existing structure, such an analysis acts to a certain extent as a substitute for the codes of practice, which for new structures constitute the rules to follow in a well-balanced and safe design. In this phase, extended surveys such as continuous monitoring or SHM are usually necessary for the in-depth analyses with regard to phases I and II for the determination of the analysis input variables. The following maintenance strategies are generally used in this phase III:

  • Corrective Maintenance (is rarely in this phase III)
  • Preventive-Condition based Maintenance (is generally applied in this phase III)
  • Preventive-Predictive Maintenance (is increasingly in use in this phase III)

Corrective maintenance strategies

A corrective maintenance strategy is also referred to as reactive maintenance, failure-based maintenance, or as a strategy of ‘run to failure’. The measures and interventions are aimed at arresting currently active processes which are causing deterioration or damage. Typically, remedial interventions involve some form of treatment or the taking of measures after damage has become apparent, presumably involving visual indications (e.g. cracking or spalling of concrete). Such actions may be required immediately (e.g. emergency repair) or may be deferred to a suitable moment later in time (when acceptable). A corrective maintenance strategy means the asset or component is used to its maximal potential (i.e. the full life time is used) and maintenance is done only when failure demands it. This can be reviewed as a default strategy, but may not be appropriate if failure is associated with unacceptable consequences or non-optimal expenditure of means (e.g. budget).

Preventive maintenance strategies

Contrary to corrective maintenance, preventive maintenance strategies aim at taking (maintenance) action prior to failure occurring, thus avoiding the consequences of that failure. For infrastructure assets, a preventive approach to maintenance is desirable as it enables early identification of issues affecting the condition of the objects, potentially enabling early preventative action being taken to minimize the negative effect on the performance of the infrastructure and, consequently, the overall cost of ownership. A preventive maintenance should be applied to objects and components thereof where it is necessary or desirable that the performance be kept above a specified minimum performance requirement. Logically, this requires knowledge on the probability of failure over time and/or use in order to determine when such (maintenance) actions are required. This is where a further distinction in maintenance strategies can be observed (fib MC2020, 2022).

Predetermined maintenance strategies

In so-called predetermined maintenance strategies, an a priori estimate is made within what timeframe or after what use failure becomes likely. Accordingly, activities set for predetermined maintenance are carried out in accordance with established intervals of time or number of units of use but without previous condition investigation. Intervals of times or number of units of use may be established from knowledge of the failure mechanisms of the item. Such estimates are based on databased, experience, etc. Based on this, a suitable moment for maintenance is picked (maximal use time within accepted risk levels). Maintenance interventions are thus planned accordingly.

Condition-based maintenance strategies

Condition-based maintenance strategies rely on (condition) information being obtained during use of the asset with the aim to better estimate when failure might occur, and when maintenance is required. In practice, a difference may be observed in how the information obtained during the use of the assets is used. For example, the observed condition can be compared to a set of e.g. criteria, thresholds, or limits. These criteria are determined based on the likely progression of condition or performance over time. If the observed condition is within acceptable bounds, no maintenance is performed. If the condition is not within acceptable bounds, this means maintenance is required and should be planned accordingly.

This may be referred to as non-predictive condition-based maintenance, as making a case specific prediction is not being made. Predictive condition-based maintenance would then refer to a strategy where information obtained through the life cycle is used to make or update a prediction of the future condition or performance. Appropriate moments for maintenance actions are based on that prediction. The predictive condition-based maintenance is an expansion of the non-predictive condition-based maintenance. The predictive condition-based maintenance entails prescribed criteria related to one (or more) condition thresholds to enable decisions about interventions based on a forecast derived from repeated analysis or known characteristics and evaluation of the significant parameters of the degradation of the item. One of the main differences between non-predictive and predictive condition-based maintenance lies in the data being analysed. While the predictive maintenance strategy relies on combination of condition monitoring and/or inspection and/or testing and analyses the past and actual condition data to estimate future condition development, the non-predictive maintenance strategy relies on historical experience, averages, and life expectancy statistics to predict when maintenance activities will be required.

Predictive condition-based maintenance strategies

The predictive condition-based maintenance strategy therefore looks for physical evidence that a failure is occurring or is about to occur. It is important to realize that this maintenance strategy is aimed at intervening before the failure occurs, on the premise that this is more economical and should have less of an impact on availability. The predictive maintenance approaches need to be underpinned by sound reliability principles and understanding of the phenomena. Furthermore, it should be mentioned that ‘condition’ may be interpreted broadly in this sense as it may include various type of information including condition, performance, properties of the asset, use, etc.

Table view of phase III maintenance strategies utilised

The table below displays, for all countries for which data is available, the phase III maintenance strategies utilised.