Maintenance Heavy Equipment Management Through Contract Models or Company it Self

—One important activity and cause high costs in the company is maintenance and in mining one of critical maintenance is heavy equipment. Issue of manpower, skill, expert and equipment population made company can’t handle the maintenance it self. Agreement to the contractor made with several contract models. This maintenance management either by company it self or by different contract models have their strong and weakness point. This research will analyze which maintenance management is better using Fuzzy AHP as a multicriteria decision making tool. Responden will selected to define the criteria and sub-criteria. The result of this research are to select maintenance management that will use as standard in the company.

contractors for the service and spare part with lump sum payments per month. Currently the heaviest equipment units at PT. Vale carries out maintenance with this type of contract.

B. SSA Contract
Maintenance contract will be carried out jointly between the contractor and PT. Vale. The contractor will perform maintenance for services while PT. Vale will contribute to the spare parts needed by maintenance.

C. On Call Contract
Maintenance contract will be carried out jointly between the contractor and PT. Vale where contractor maintenance activities are categorized into several activities / work packages.
The choice of maintenance strategy requires a method for assessing from many of the criteria that arise from maintenance problems. One method for multi-criteria decision making is the Analytic Hierarchy Process. AHP method is often used in previous studies related to suppliers/contractors to determine supplier performance, determine supplier selection. Previous studies have used AHP to determine the type of contract awarded, previous research on grocery stores (S. M. Tazim Ahmed & Chitra Karmaker, Journal of Supply Chain Management Systems). In this study using fuzzy AHP, which is a method of combining fuzzy and AHP which is better at solving problems. In contrast to this study, where previously the research was for contracts for providers of foodstuffs to be sold, whereas this study was for heavy equipment maintenance service contracts.
The objective of this research is: (1) Knowing the criteria for determining system maintenance. (2) Determine the maintenance system that should be the standard to use in the company.

A. AHP
The AHP developed by Professor Thomas Saaty in 1980 made it possible to arrange decisions hierarchically (to reduce their complexity) and show the relationship between goals (or criteria) and possible alternatives. Perhaps the greatest advantage of this method is that it allows the inclusion of intangible objects such as experience, subjective preferences and intuition, in a logical and structured manner. the greatest advantage of this method is that it allows the inclusion of intangible objects such as experience, subjective preferences and intuition, in a logical and structured manner. This research use AHP for 3 following steps.

Maintenance Heavy Equipment Management Through Contract Models or Company it Self
Andi Afiyuddin and Adithya Sudiarno Department of Industrial and Systems Engineering, Institut Teknologi Sepuluh Nopember, Surabaya E-mail: a.afiyuddin@gmail.com P

1) Construct Hierarchy
Creating hierarchical forms of various elements as principle objectives, goals that are influenced by these criteria or criteria that are influenced by sub-criteria and are nothing but different substitutes available for the problem ( Figure 1).

2) Pair-Wise Comparison (Determining Weights)
The comparison matrix between factors is the nxn dimension box matrix. The matrix component on the diagonal of this matrix takes 1 value. When i = j, the component on the diagonal of the comparison matrix takes 1 value; because the related factor has compared with itself in this situation. Comparing factors is done according to their importance to each other and reciprocally. One-by-one and reciprocally comparing the importance scale of factors, using a comparison scale in Table 2.

3) Consistency in Factor Comparisons was Calculated
AHP suggests a process for measuring the consistency of this comparison. Finally, by obtaining a Consistency Ratio (CR), there has been an opportunity to test the consistency of priority vectors and also the consistency of pair comparisons between criteria. The essence of CR calculation is based on comparison of the number of criteria and coefficients, called the Main Value (ƛ) by the AHP. In principle, from doubling the comparison matrix A and priority vector W, column vector D is obtained for calculation ƛ After ƛ is calculated, the Consistency Index (CI) can be calculated according to the following formula. (2) And finally calculate the value of the ratio consistency with the formula. = Consistency is acceptable if the CR value <0,100.
B. Fuzzy AHP AHP combined with fuzzy logic known as Fuzzy AHP is a popular method for dealing with uncertainty and helps decision makers in complex problems with various conflicting criteria (Kubler et al., 2016). The Fuzzy AHP model (FAHP) is based on fuzzy set theory, where the membership of a given element is determined by the membership function. The value of the fuzzy decision variable is explained by the membership function which is between zero and one.
Chang (1996) defines AHP intensity values into triangular fuzzy scales. The fuzzy triangle scale used by Chang can be seen in Table 3. Fuzzy AHP step in research as following:

1) Calculate the Average Value of Fuzzy Geometric
The initial step is to determine the geometric mean of Fuzzy numbers with the formula:

2) Calculate the Value of Fuzzy Weights
Calculate the value of Fuzzy weights with the formula:

3) Perform the Fuzzy Element Defuzzification Process
Perform the fuzzy element defuzzification process using the Center of area (COA) method.

4) Normalization of Mi Values
Normalization of Mi values by calculation: This normalized priority weight calculation procedure must be applied to the evaluation of specific alternatives for each criterion (alternative preference matrix).

2) Pair-Wise Comparison
Pair-wise comaparison using questionnaire to 5 respondent. Result of from the questionnaire shown in the example responden 1 Table 4. After find the example responden in Table 4, next step is to find the Consistenncy Ratio. Consistency ratio for responden 1 shown in Table 5.

B. Fuzzy AHP
Data from respondents is converted into triangular fuzzy numbers (TFN) using scale in Table 3 mention before. Matrix Fuzzy number matrix of 5 respondents were converted using the geometric mean method, and got the results in Table 6. Following process fuzzy step mention in section II, result of criteria weighting shown in Table 7.
After result in Table 7, process continue to find score of alternative fo each criteria, the result shown in Table 8.
From the Table 8 shows that the MARC alternative has the greatest value compared to the three other alternatives that is equal to 0.3490. The second alternative is SSA worth 0.2003 and the alternative with the smallest weight is the on call alternative.

IV. CONCLUSION
Fuzzy AHP is a method for dealing with uncertainty and helps decision makers in complex problems with various conflicting criteria. Fuzzy AHP is better method to reduce subjective comparing to AHP. Research shows that the method can be used to choose strategy maintenance in company and as the result is MARC alternative is the best strategy of maintenance that company should use with high score in quality aspect.