Presenting a Model Based on Fuzzy Application to Optimize the Time of IBS Projects in Gas Refineries

Nowadays, the construction industry has started to embrace IBS as a method of attaining better construction quality and productivity and reducing risks related to occupational safety and health. The built of prefabricated component in factories reduces many problems related to lack of purposing uncertainty in scheduling calculation and time management of projects. In the case of using IBS method for managing time in projects, former studies such as Allan Tay’s research, indicates that this method can save up at least 29% of overall completion period versus the conventional method. But beside mentioned advantages of this technical method, the projects could be optimized more and more in scheduling calculations. This issue is critical in gas refineries, since special parameters such as risk of spreading poison H2S gas and mandatory of performing projects in short time period events such as maintenance overhauls demands to perform projects in optimum time. Custom scheduling calculation of project planning uses the Critical Path Method (CPM) as a tool for Planning Project’s activities. The researches of this paper’s authors indicated that Fuzzy Critical Path Method (FCPM) is the best technique to manage the uncertainty in project scheduling and can save up the construction project’s time versus the custom methods. This paper aims to present a model based on fuzzy application in CPM calculations to optimize the time of Industrial Building System.


Introduction
IBS can be defined as a construction system which components are manufactured in a factory, on or off-site, Positioned and assemble in to structures with minimal additional site work [1].The typical classifications is shown in Fig. 1, [2].Former studies indicate that IBS can save up about 29% of overall completion time versus the conventional method [3].
Beside mentioned advantages of these technical methods, the projects could be optimized more and more in scheduling calculations.The researches of this paper's authors indicated that Fuzzy Critical Path Method (FCPM) is the best technique to manage the uncertainty in project scheduling and can save up the construction project's time versus the custom methods.approach.In this method, fuzzy function defines the time of project activities to manage their uncertainties.For understanding the main concepts of FCPM, consider the project network indicated in Fig. 3.This project network is a part of a small one-story Industrial building System project that contained of excavation, concreting and installing the building structures.The resistance system against the earthquake is A.D.A.S bracing.As it could be seen from Fig. 2, 10 of whole 11 activity times have triangular fuzzy type format and only the remaining one is in trapezoidal form.In order to determine the project time According to CPM calculation, it is necessary to rank the fuzzy numbers and select the maximum.For ranking the fuzzy numbers brings from CPM calculations, 5 methods available.The result shows in Fig. 3 [4].

Figure 3. Project total time calculated based on different fuzzy ranking methods
In FCPM calculations, as the results indicate, selecting the fuzzy ranking method for each project scheduling has main influence on determination of project total time and critical path.Also suitable fuzzy ranking method, compatible to project nature should be considered by project management team.The scheduling calculation of this paper's authors indicated that Fuzzy Critical Path Method (FCPM) can save up project total time versus the custom project management methods.

Presenting a fuzzy base model to optimize the time of (IBS) projects
For implementing a model based on Fuzzy technique In order to optimize the time of (IBS) Projects various membership functions and linguistic variables have been defined by judgment of experts.Linguistic variables, such as Site Organization, weather, Labor Skills and Quality of equipment, need to be translated in to mathematical measures.The value of these considered variables can be classified in to 5 types: Very Poor, Poor, Medium, High and Very High.These are not clearly defined but are meaningful classifications.As described in the example of section 2 (the project network indicated in Fig. 2) project network calculation is a very time consuming process.So we need to use software tools for the optimizer model.The research of this paper indicated that, fuzzy toolbox of MATLAB is the best tools for our goal.Output is a crisp result which is obtained after undergoing the process of: Pre-Processing (1), Fuzzification (2), Rule base (3), Inference Engine (4) and Defuzzification (5) [5]- [12].The output can be decided by user to obtain required result after the whole inference process, which can be desired result of whole designed fuzzy system.In the first step the scenario of analysis is designed.

The result of implementation of proposed model in a gas refinery
Corresponding author of this paper has implemented the Recommended model to manage the project of a specific Gas Refinery in east-north of Iran in statistical society of 30 selected projects among all of industrialized projects (Selected according the Cochran formula).Table 2 indicates the configuration of selected projects.The members of expert team in this research were Chosen from contractors, consultant and supervisors of owner and the time of research took about two years between 2014 up to 2016.Table 3 indicates the identification of research expert team and the result of analysis is shown in Fig. 6.
The result of analysis indicates the implementation of the recommended model, lead to reducing the total time of selected project (as a minimum 7% of project total time) versus the custom methods.The rate of this reduction estimated by Corresponding Author, and the result is according to Fig. 6.

Conclusions
In the field of using new technical method in construction industry such as IBS, many studies indicate that these new technical methods can save up at least 29% of overall completion period versus the conventional method.So when these new technical methods are merged by intelligent project planning approaches, the results can improve more and more.Custom scheduling calculation of project planning uses the Critical Path Method (CPM) as a tool for measuring activities time progress.
Whereas CPM has the main weak point which is related to lack of purposing uncertainty in scheduling calculation.The research of this paper's authors indicated that Fuzzy Critical Path Method (FCPM) that added Fuzzy approach to CPM is the best technique to manage the uncertainty in project scheduling and it can save up as a minimum 7% of project total time versus the custom project management methods.
So when this project planning approach is merged with new technical method in construction industry such

Figure 1 .
Figure 1.Industrialized building system types (Box-Frame, Beam-Panel system and panel systems)

Figure 4 .
Figure 4. Categorization of membership functions So in first step the entire project activities will be converted to any of categories mentioned above.The values of membership function may also change with respect to activity and the results obtained from the simulation of different graphs are thus interpreted and modified as per requirements of duration change.Second step is the schedule calculations and analysis.As described in the example of section 2 (the project network indicated in Fig.2) project network calculation is a very time consuming process.So we need to use software tools for the optimizer model.The research of this paper indicated that, fuzzy toolbox of MATLAB is the best tools for our goal.

Figure 5 .
Figure 5. Pictorial view of fuzzy inference system in MATLAB

Table 1 .
Building system classification according to relative weight of component 2 Fuzzy critical path method (FCPM)FCPM is an extension of Critical Path Method by fuzzy

Table 2 .
Configuration of Selected Projects for Research Calculation and Analysis

Table 3 .
The identification of expert team of research Figure 6.Research Results (Project ID -rate of Reduction in Total Time)