MAINTENANCE STRATEGY SELECTION BASED ON HYBRID AHP-GP MODEL

SUZANA SAVIĆGORAN JANAĆKOVIĆMIOMIR STANKOVIĆ

University of Niš, Faculty of Occupational Safety in Niš

CONTENT

INTRODUCTION MAINTENANCE STRATEGIES AHP-GP MODEL FOR MAINTENANCE

STRATEGY SELECTION CONCLUSION

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.

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

Start

Divide the system into manageable subsystems (n)

Consider subsystem si i=1,2,3,…,n

Identify the element present in the subsystem si: ej=1,2,3,…,m

Consider the element ej: j=1,2,3,…,m

Develop hierarchical structure of maintenance selection criteria

Perform AHP analysis by means of pairwise comparison

Define objective function and problem constraints using goal programming

based on AHP scores (global and local)

Select the appropriate maintenance strategy

Any element left ?

Compare the proposed maintenance strategy with the existing strategy

Any subsystemleft?

End

No

No

Yes

Yes

AHP-GP MODEL FOR MAINTENANCE STRATEGY SELECTION

The methodology involves the following basic steps:1. Application of AHP methodology2. Application of the GP based on AHP results3. Selection of the appropriate maintenance strategy.

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.

AHP methodology

Hierarchy scheme for maintenance strategy selection

Reliability Availability Safety Costs

Corrective Preventive Proactive

Maintenance strategyGoal level

Criteria level

Alternative level

AHP methodology

Scale of AHP pairwise comparison

Level Importance Explanation

1 Equal The equal contribution of two factors to the objective

3 ModerateExperience and judgment slightly favor one factor over another one

5 StrongExperience and judgment strongly favor one criterion over another one

7 Very strongA factor is favored very strongly over another; its dominance demonstrated in practise

9 ExtremeThe evidence favoring one factor over another is of the highest possible of affirmation

AHP methodology

Pairwise comparisons at each level are presented in the square matrix form:

aij are the judgments or the relative importance of

alternative i over alternative j, and

aij=1 for i=j and aij=1/aji for i≠j

nnnn

n

n

aaa

aaa

aaa

A

...

............

...

...

21

22221

11211

AHP methodology

Relative weights determination Eigenvector of criteria:

Eigenvectors of alternatives for every single criterion (or local scores):

),,,( CSAR wwwww

),,( 3,2,1, RRRR SSSS

),,( 3,2,1, AAAA SSSS

),,( 3,2,1, SSSS SSSS

),,( 3,2,1, CCCC SSSS

AHP methodology

Checking result consistency

consistency index

consistency ratio

random index

If CR≤0,1 result is consistency.

1max

n

nCI

RI

CICR

n 1 2 3 4 5 6 7 8

RI 0 0 0,52 0,89 1,11 1,25 1,35 1,40

AHP methodology

Global priority determination

),,( 3,2,1, AHPAHPAHPAHP SSSS

1,1,1,1,1, CCSSAARRAHP SwSwSwSwS

2,2,2,2,2, CCSSAARRAHP SwSwSwSwS

3,3,3,3,3, CCSSAARRAHP SwSwSwSwS

Reliability Availability Safety Costs

Corrective Preventive Proactive

Maintenance strategyGoal level

Criteria level

Alternative level

Goal Programming

General model of goal programming

objective function:

limits:

1

(min) ( )r

k k k kk

Z w P d d

, , 0

CX d d F

AX d d B

X d d

Goal Programming

The goal programming model of maintenance strategy selection

3,2,1,

3,2,1,

3,2,1,

3,2,1,

3,2,1,

CCC

SSS

AAA

RRR

AHPAHPAHP

SSS

SSS

SSS

SSS

SSS

C),,( 321 xxxX

(1, , , , )R A S CF T T T T

)()((min) 21 CCSSAARRAHP dwdwdwdwPdPZ

Goal Programming

133,22,11, AHPAHPAHPAHPAHP ddxSxSxS

RRRRRR TddxSxSxS 33,22,11,

AAAAAA TddxSxSxS 33,22,11,

SSSSSS TddxSxSxS 33,22,11,

CCCCCC TddxSxSxS 33,22,11,

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 (x1, x2 and x3); values od priority factors (P1 and P2); deviation from the defined target values ( and ,

k=1,…, r); and realized target values .

Based on the normalised values of real variables (x1 is the corrective maintenance strategy, x2 is the preventive maintenance strategy, x3 is the proactive maintenance strategy), the optimal strategy of maintaining the technical system is chosen.

kd

kd

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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