1. MAINTENANCE STRATEGY SELECTION BASED ON HYBRID AHP-GP MODEL SUZANA SAVIĆ GORAN JANAĆKOVIĆ MIOMIR STANKOVIĆ University of Niš, Faculty of Occupational Safety in Niš

2. CONTENT INTRODUCTION MAINTENANCE STRATEGIES AHP-GP MODEL FOR MAINTENANCE STRATEGY SELECTION CONCLUSION

3. INTRODUCTION In the last several years, multi-criteria decision making has been recommended as a method of selecting the strategy, policy and method of maintaining technical systems. In this paper, an integral approach based on the method of Analytical Hierarchy Process and Goal Programming is used for maintenance strategy selection. Reliability, availability, safety and costs are used as decision making criteria, while corrective, preventive and proactive maintenance strategies are used as alternatives.

4. MAINTENANCE STRATEGIES The highest level of system maintenance refers to maintenance strategy. The basic maintenance strategies are: Corrective maintenance strategy Preventive maintenance strategy Proactive maintenance strategy

5. AHP-GP MODEL FOR MAINTENANCE STRATEGY SELECTION The methodology involves the following basic steps: 1. Application of AHP methodology 2. Application of the GP based on AHP results 3. Selection of the appropriate maintenance strategy.

6. AHP methodology The AHP method involves the following steps: The overall goal (objective) is identified and clearly defined; The criteria, sub-criteria and alternatives which contribute to the overall goal are identified; The hierarchical structure is formed; Pairwise comparison is made; The priority weights vector is estimated by using the eigenvalue method; The consistency of the judgments is checked; The global priority vector is calculated.

7. AHP methodology Hierarchy scheme for maintenance strategy selection

8. AHP methodology Scale of AHP pairwise comparison LevelImportanceExplanation 1Equal The equal contribution of two factors to the objective 3Moderate Experience and judgment slightly favor one factor over another one 5Strong Experience and judgment strongly favor one criterion over another one 7Very strong A factor is favored very strongly over another; its dominance demonstrated in practise 9Extreme The evidence favoring one factor over another is of the highest possible of affirmation

9. AHP methodology Pairwise comparisons at each level are presented in the square matrix form: a ij are the judgments or the relative importance of alternative i over alternative j, and a ij =1 for i=j and a ij =1/a ji for i≠j

10. AHP methodology Relative weights determination Eigenvector of criteria: Eigenvectors of alternatives for every single criterion (or local scores):

11. AHP methodology Checking result consistency consistency index consistency ratio random index If CR≤0,1 result is consistency. n12345678 RI000,520,891,111,251,351,40

12. AHP methodology Global priority determination

13. Goal Programming General model of goal programming objective function: limits:

14. Goal Programming The goal programming model of maintenance strategy selection

15. Goal Programming

16. Selection of maintenance strategy To solve the problem of goal programming, a modified simplex procedure is used. The results of applying this procedure are the following: values of real variables (x 1, x 2 and x 3 ); values od priority factors (P 1 and P 2 ); deviation from the defined target values ( and, k=1,…, r); and realized target values ​​. Based on the normalised values of real variables (x 1 is the corrective maintenance strategy, x 2 is the preventive maintenance strategy, x 3 is the proactive maintenance strategy), the optimal strategy of maintaining the technical system is chosen.

17. CONCLUSION Using the AHP method, global and local scores are determined They are used as coefficients of the appropriate goals and sub-goals of GP methods They are also used to define the target values of criteria The result of applying the hybrid AHP-GP model is the selection of maintenance strategy (corrective, preventive or proactive).

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