Comparison of Two Simulation Software for Modeling a Construction ...

2011 Third International Conference on Computational Intelligence, Modelling & Simulation

Comparison of Two Simulation Software Systems for Modeling a Construction Process Amin Nikakhtar

Kuan Yew Wong

Faculty of Mechanical Engineering Universiti Teknologi Malaysia Skudai, Malaysia [email protected]

Faculty of Mechanical Engineering Universiti Teknologi Malaysia Skudai, Malaysia [email protected]

Mohammad Hossein Zarei

Ashkan Memari

Faculty of Mechanical Engineering Universiti Teknologi Malaysia Skudai, Malaysia [email protected]

Faculty of Mechanical Engineering Universiti Teknologi Malaysia Skudai, Malaysia [email protected] Examples of simulation software used in simulating construction processes are SDESA, MicroCYCLONE, STROBOSCOPE, etc. In addition to these packages, there are generic simulation packages with better graphical environments. ARENA 13 and WITNESS 2004 Manufacturing Edition are two simulation tools with powerful animation features. This paper is aimed at comparing the features of two simulation software, WITNESS 2004 Manufacturing Edition and ARENA 13. To do this, a construction process is simulated using ARENA 13 and WITNESS 2004 Manufacturing Edition. Also, the reports generated by both of the simulation software are compared in order to provide a valid comparison. The paper is presented as follows. First, the difficulties in construction industry which bring about the application of simulation in construction are discussed. Second, different simulation software and languages used for simulating a construction process are reviewed. Third, two simulation models are constructed for a case study, concrete pouring of beams and slabs, using ARENA 13 and WITNESS 2004 Manufacturing Edition. Fourth, these models are verified and validated. Finally, the reports are compared in order to highlight different features of each of the software.

Abstract— Construction process complexities lead to many difficulties imposed on construction planners and designers who are facing with different issues such as developing new methods or solving problems during a construction process. In order to solve these problems in construction industry, simulation can be an acceptable solution. In this regard, graphical methods have become a useful tool for process simulation. To do construction process simulation with a suitable graphical display, many simulation software are developed such as PROMODEL, SDESA, and etc. This paper aims at comparing two simulation tools (software), ARENA 13 and WITNESS 2004 Manufacturing Edition, for making a construction process simulation model. It shows that both software produce almost the same results and outputs for a given construction process. Also, the paper shows different kinds of features and reports provided by ARENA 13 and WITNESS 2004 Manufacturing Edition. Keywords-construction process simulation;simulation software;ARENA 13;WITNESS 2004 Manufactring Edition

I.

INTRODUCTION

The Designing of a construction process is becoming more complicated in construction industry. This complexity leads to many difficulties imposed on construction planners and designers who are faced with different issues such as developing new methods or solving problems during a construction process. Because of the existence of complex relationships in construction processes, describing a construction process is difficult [1]. In order to solve these problems in construction industry, simulation can be an acceptable solution which is applied for designing the construction operations and analyzing their behavior [2, 3]. With the advancement of graphical computer techniques, graphical methods have attracted attention to themselves for using them as useful tools for process simulation [4]. There are various simulation software that provide environments to implement any new principle. 978-0-7695-4562-2/11 $26.00 © 2011 IEEE DOI 10.1109/CIMSim.2011.42

II.

COMPUTER SIMULATION OF CONSTRUCTION PROCESSES

In daily construction practices, many decisions related to the construction processes are made by construction designers. In some cases, decisions are made with unforeseen outcomes. The reason for this is that visualizing all the processes of construction operations is difficult [1]. In addition, in real-life, it is preferable to test a construction process to examine its performance prior to implementation. From an economic perspective, it is not suitable to test the process physically since the physical 200

testing of a process is time consuming and very expensive [5]. In order to cope with the above mentioned issues and problems, simulation can be a useful tool. It is a convenient technique used to model actual construction operations. It provides an environment in which decision makers can better analyze and understand the problems by doing experiments in a low-cost environment [6]. III.

Automation as a new generation simulation environment. It uses the SIMAN processor and simulation language. It can be used for both commercial and academic purposes [13]. The fundamental elements of modeling in ARENA 13 are called modules that are built around SIMAN. In order to build a simulation model with ARENA 13, a modeler first selects the appropriate modules from a template panel and places them on the simulation environment. After that, these modules are connected to each other graphically in order to show the flow of transactions between them. Finally, the required and considered codes are written in each module [14]. On the other hand, WITNESS 2004 Manufacturing Edition is simulation software that is used for designing systems and demonstrating their operation in reality. WITNESS 2004 Manufacturing Edition can help people by predicting and solving problems related to production bottlenecks, overly-idle resources, etc [15]. In WITNESS 2004 Manufacturing Edition, models are built based on fundamental parts called elements or building blocks. Anything used for constructing a model in WITNESS 2004 Manufacturing Edition is an element. In order to build a simulation model first the required elements are defined then, displayed and detailed. In contrast to ARENA 13 that modules are connected to each other graphically, in WITNESS 2004 Manufacturing Edition, the connections can be defined as codes in each element. After defining the connections, finally, the required codes are written in each element.

CONSTRUCTION PROCESS SIMULATION SYSTEMS

Using simulation in construction processes has been broadly done in various situations. For instance, introducing lean construction concept into construction industry caused simulation to be applied in cases pertaining to work flow variability [7]. Also, Tommelin [8] evaluated the applicability of a production concept in a pipe-spool installation process with the aid of simulation. Today there are various simulation software developed for simulating different construction processes such as SDESA, PROMODEL, MicroCYCLONE, Extend, STROBOSCOPE, etc. In the next section a brief review of different features of the mentioned software is done. IV.

COMPUTER SIMULATION SOFTWARE

Simulation tools provide a realistic approach for doing analysis since they considered the randomness in activity duration and the influence of resource availability as a constraint to construction work flow [9]. Typical simulation software used in construction process simulation are SDESA, MicroCYCLONE, and STROBOSCOPE. SDESA is a simple platform based on activity modeling that makes construction simulation as easy as applying the current construction planning approaches such as critical path method (CPM). MicroCYCLONE is a simulation program developed specifically for modeling cyclic processes. It is based on CYCLONE modeling elements. CYCLONE, which stands for cyclic operation network, is the best known simulation language designed for simulating construction operations and activities [10]. Finally, STROBOSCOPE is a simulation language applied for construction activity simulation. It can also be used in domains other than construction industry [11]. It aims at modeling uncertainties related to activity duration, quantity, and resource assignment [12]. In addition to the above simulation software, there are computer simulation packages which have more attractive graphical environments. ARENA 13 and WITNESS 2004 Manufacturing Edition are two examples of this type. In the next section, a brief review of different features of these two software packages is done and after that the rest of the article is about doing a simulation study for a construction operation using theses two software. V.

VI.

CASE STUDY: A CONCRETE POURING OPERATION OF BEAMS AND SLABS

The case study is part of a concrete building construction located in the city of Mashhad, Iran. It consists of two floors and each floor, according to design specifications, needs 420 cubic meters of concrete to be completed. The concrete operations are divided into two main operations. The first one is concrete pouring of slabs and beams and the second is concrete pouring of walls and columns. In this paper, the authors aim at focusing on concrete pouring operation of beams and slabs which needs 301 cubic meters of concrete. The operation applies mobile pumping for concrete pouring. Concrete trucks that contain seven cubic meter of concrete are used for hauling concrete to the construction site. VII. PROCESS MAPPING AND DATA COLLECTION In the first step toward building the simulation model of a construction process, activities of the process and their sequences, labors and resources used, and flow of the work were determined based on the actual behavior. Interactions between resources, activities, and the flow of information in any construction process can be depicted by process mapping. Figure 1 illustrates the schematic process map of concrete pouring operations using operation process chart (OPC) symbols. More details of the process are considered in the simulated model.

OVERVIEW: ARENA 13 VS. WITNESS 2004 MANUFACTURING EDITION

ARENA 13 is simulation software developed by System Modeling Company and acquired by Rockwell

201

model reflects the actual behavior of the process [17]. In the next two sections, the verification and validation are done for both of the models constructed by ARENA 13 and WITNESS 2004 Manufacturing Edition.

A simulation model of a construction process needs random durations for each activity. Therefore, after developing the process map of the construction process, data related to the duration of each activity were gathered. Having collected the data sets, a probability distribution should be fitted to each data set in order to reflect the randomness of the process. For doing data collection, the “stop watch” method was used in order to gather activity duration data. In this method, first of all the activities were recorded by a camera and after that the duration of each activity was recorded using a chronometer. It should be noted that recording should be done in a way that do not affect the performance of workforces. For fitting a probability distribution to a sample data, various computer packages can be used. EasyFit, which was used in this study, is one commercial package that fits a wide variety of distributions to sample observations. Using EasyFit, many continuous distribution functions (such as Exponential, Beta, Gamma, Uniform, etc.) were tested against the collected data, and the most promising one according to the goodness-of-fit tests is selected. Actually, the goodness-of-fit tests (the chi-square, Anderson Darling and the Kolmogorov–Smirnov tests) were used to validate the assumed distribution functions.

Figure 2. Simulated model of concrete pouring process by WITNESS 2004

Next member

Construction Site Entrance

Concrete hauling

Spreading

Yes Vibrating Is pump busy? (Queue)

NO

Slump Testing

Concrete pumping

Concrete truck finished?

NO

Next member

Yes

Figure 3. Simulated model of concrete pouring process by ARENA 13

Finishing

Waiting

X. VIII. MODEL DEVELOPMENT

Having defined the best probability distributions, it is time to construct the simulation model of the considered construction process. The process map, distribution’s parameters, and actual behaviors were used to accurately model the conventional concrete pouring operations via ARENA 13 and WITNESS 2004 Manufacturing Edition. Figures 2 and 3 illustrate the models constructed by WITNESS 2004 Manufacturing Edition and ARENA 13, respectively. IX.

MODEL VERIFICATION

Verification, more specifically, includes inspection of the logic of the model, performing simulation test runs, tracing the entities in sample path trajectories, and evaluating the consistency of statistics of the model [19]. In order to verify the models built in ARENA 13 and WITNESS 2004 Manufacturing Edition, transactions were checked to see if they go where they are supposed to go and if they do what they are supposed to do under every condition. For instance, performance verification of labor 2 in both models is explained in detail through the precise tracing of the activities’ behavior in the model. To do so, the labor 2’s performance results are compared with the total throughput in a random run of the model. For ARENA 13, results of a test run in Table I demonstrate that labor 2 has been busy in 46.44% of the total process duration which is 186.11 minutes. It means that the time that labor 2 spends on pumping a cubic meter of concrete in the entire concrete pouring process is equal to 86.43 minutes (46.44%*186.11). On the other hand, according to collected data and fitted distribution for pumping, labor 2

Figure 1. General process mapping of concrete operations

VERIFICATION AND VALIDATION OF THE MODEL

A process of modeling will be successful when the simulated model accurately reflects the present workflow process. Therefore, before any experimentation is done, it is essential to verify and validate the model [16, 17, and 18]. Model verification ensures that the model behaves as expected and it does not have any logical error. On the other hand, model validation ensures that the simulated

202

estimate of m number of runs; α= level of confidence; ε= allowable percentage of error; and t , / = critical value of the two-tailed t-distribution at a level of significance, given m-1 degrees of freedom. The mean and standard deviation estimate are determined for an initial m number of runs of five. Then at a level of confidence of 95% and allowable percentage of error of 5%, t , . is equal to 2.776. Equation (1) represents that the number of simulation runs to achieve the desired level of accuracy is 4 replicates or greater. Table III shows the calculation of X m and S m . It should be noted that the data gathered for estimating the mean and standard deviation are the cycle time of the construction process achieved by running the model. After determining the number of simulation runs, validation was done for the simulation model constructed by both ARENA 13 and WITNESS 2004 Manufacturing Edition. As mentioned before, the actual cycle time was compared with the results of the five simulation runs. Table IV shows the data for validation. It shows that the averages of five simulation runs are 197.82 and 199 for ARENA 13 and WITNESS 2004 Manufacturing Edition model, respectively. As can be seen in Table IV, the percentage variations in simulation prediction are 3.88 and 3.40 for ARENA 13 and WITNESS 2004 Manufacturing Edition respectively, which is considered acceptable.

averagely pumps one cubic meter of concrete in 0.93 minutes. Therefore labor 2 pumps the concrete 92.93 times (86.37/0.93) in the examined test run. The difference between the above total seized number and the number produced by ARENA 13 is 2.12% which is considered acceptable for the model. For WITNESS 2004 Manufacturing Edition, the procedure is the same as for ARENA 13. As can be seen from the results of WITNESS 2004 Manufacturing Edition in Table II, labor 2 has been busy in 44.68% of the total process duration which is 190.51 minutes. Therefore, the time labor 2 spends on pumping is 85.119 minutes (44.68*190.51). Given that the average time labor 2 spends on pumping one cubic meter of concrete is 0.93 minutes, labor 2 pumps the concrete 91.52 times. The calculated number of jobs is equal to the number calculated by WITNESS 2004 Manufacturing Edition, shown in Table II. Similarly, all the transactions, modules, linkages and resources were carefully examined and subsequently, necessary modifications were done to solve the probable problems and verify the model. TABLE I.

RESOURCE RESULTS OF THE MODEL FOR LABOR 2 IN ARENA 13

Usage Instantaneous Utilization Scheduled Utilization Number Scheduled Total Number Seized Number Busy

TABLE II.

Labor2 Average 0.464 0.464 1.000 91.000 0.464

Minimum 0 1.000 0

Maximum 1.000 1.000 1.000

TABLE III.

CALCULATION OF MEAN AND STANDARD DEVIATION ESTIMATE FOR DETERMINING THE NUMBER OF SIMULATION RUNS

RESOURCE RESULTS OF THE MODEL FOR LABOR 2 IN WITNESS 2004 MANUFACTURING EDITION Name %Busy %Idle Quantity No. Of Jobs Started No. Of Jobs Ended No. Of Jobs Now Avg Job Time

XI.

Simulation Cycle Time (Minutes)

Labor2 44.68 55.32 1 91 91 0 1.03

Replication

1

204.51

2

200.76

3

196.09

4

201.61

5

186.11

̄

197.816 7.209

MODEL VALIDATION

Once the examiner is convinced with the verification stage, validation activities can get under way. Model validation is a critical step to construct a credible simulation model. The standard approach of validation is to compare the collected actual data to the simulated model outputs. One of the appropriate factors to show how actual process and simulated process are alike is cycle time [19]. In order to do validation, first the number of simulation runs to produce the desired level of accuracy should be determined. To do so, Ahmed [20] proposed the following formula, given the m initial replications: ,

X

/

TABLE IV.

(1)

Where N m = number of simulation runs to achieve the desired level of accuracy; X m = the mean estimate of an initial m number of runs; S m = the standard deviation

203

Replication

Simulated Cycle Time (Minutes)ARENA 13

1 2 3 4 5 Average Variation (%)

204.51 200.76 196.09 201.61 186.11 197.82 3.88

VALIDATION DATA Simulated Cycle Time (Minutes)WITNESS 2004 Manufacturing Edition 198.27 206.57 190.51 189.78 208.84 198.79 3.40

Actual Cycle Time (Minutes)

205.8

A significant feature of ARENA 13 is the ability to categorize the activities into different types such as valueadded, non value-added, waiting, transfer, and others. This is very useful in determining the different time spent on different types of processes. This can help a manager to improve the system by minimizing non value-adding processes. However, this is not provided by WITNESS 2004 Manufacturing Edition. Tables VIII and IX show the process reports of the case study provided by WITNESS 2004 Manufacturing Edition and ARENA 13, respectively.

XII. REPORTS ANALYSIS After verifying and validating the simulation model, it is time to get the results produced by the software. ARENA 13 and WITNESS 2004 Manufacturing Edition provide simulation reports that can be helpful for evaluating the simulated system. These reports include report of the part (entity) performance, labor performance, machine performance, etc. This section aims at presenting some typical reports generated by ARENA 13 and WITNESS 2004 Manufacturing Edition in order to show different features of the software. As an instance, the queue (buffer) report generated by ARENA 13 is shown in Table V. Also, WITNESS 2004 Manufacturing Edition generates this report as shown in Table VI. As can be seen in both tables, the results produced by ARENA 13 and WITNESS 2004 Manufacturing edition are very near to each other. As an instance, in ARENA 13, the average amount of time that an entity, one cubic meter of concrete, waits in the queue of Finishing is 0.31 minutes while in WITNESS 2004 Manufacturing Edition this time is 0.39 minutes. This minor difference shows that these two simulation packages generate the same output for a verified and valid model. An attractive feature of the reports generated by WITNESS 2004 Manufacturing Edition is the charts generated by each report. For example, figure 4 represents a labor report produced by WITNESS 2004 Manufacturing Edition in which the bar chart of the report table is also presented. However, ARENA 13 does not have this feature for generating the chart of each report. The labor report produced by ARENA 13 is shown in Table VII in order to compare it with the labor report of WITNESS 2004 Manufacturing Edition.

Figure 4.

Labor report generated by WITNESS 2004 Manufacturing Edition

TABLE VII. TABLE V.

QUEUE REPORT GENERATED BY ARENA 13

Queue Detail Summary Time Name Waiting Time (Minute) Spreading 2.53 Vibrating 0.08 Finishing 0.31 Other Name Number Waiting Spreading 1.12 Vibrating 0.04 Finishing 0.14

Name Labor1 Labor2 Labor3 Labor4 Labor5 Labor6 Labor7

Inst Util 0.18 0.46 0.38 0.38 0.36 0.36 0.43

TABLE VIII. TABLE VI.

QUEUE REPORT GENERATED BY WITNESS 2004 MANUFACTURING EDITION

Name Total In Total out Now In Max Min Avg Size Avg Time (Minute)

Vibrating Queue 91 91 0 1 0 0.05 0.12

Finishing Queue 91 91 0 2 0 0.17 0.39

Spreading Queue 91 91 0 7 0 1.07 2.45

204

LABOR REPORT GENERATED BY ARENA 13 Resource Detail Summary Usage Num Num Num Busy Sched Seized 0.18 1.00 13.00 0.46 1.00 91.00 0.38 1.00 91.00 0.38 1.00 91.00 0.36 1.00 91.00 0.36 1.00 91.00 0.43 1.00 91.00

Sched Util 0.18 0.46 0.38 0.38 0.36 0.36 0.43

PROCESSES REPORT GENERATED BY WITNESS 2004 MANUFACTURING EDITION

Name

%Idle

%Busy

No. Of Operations

Pumping

55.32

44.68

91

Spreading

64.35

35.65

91

Vibrating

66.41

33.59

91

Finishing

58.64

41.36

91

Ready to Pump

82.52

17.48

13

TABLE IX.

PROCESSES REPORT GENERATED BY ARENA 13

[5]

Process Detail Summary Time per Entity Value Added Time (Minute) 1.28 0.97 1.04 1.04 2.86 2.86 3.38 0.85 0.88 0.80 Accumulated Time Value Added Wait Time Time (Minute) (Minute) 88.56 27.77 94.98 0.00 37.22 0.00 77.66 229.92 72.90 7.54 Others Number In Number Out 91.00 91.00 91.00 91.00 13.00 13.00 91.00 91.00 91.00 91.00 Total Time (Minute)

Finishing Pumping Ready to Pump Spreading Vibrating

Finishing Pumping Ready to Pump Spreading Vibrating

Finishing Pumping Ready to Pump Spreading Vibrating

[6]

Wait Time (Minute) 0.31 0.00 0.00 2.53 0.08

[7]

[8]

[9]

[10]

[11]

[12] [13] [14]

XIII. CONCLUSION

[15]

Simulation software provides a realistic approach for analysis by means of graphical methods and visualization. In this study, two simulation packages, ARENA 13 and WITNESS 2004 Manufacturing Edition were used for developing a construction process model in order to compare them with each other. The results generated by both packages are fairly valid and realistic. It was shown that the outputs produced by ARENA 13 and WITNESS 2004 Manufacturing Edition are almost the same. Also, different features of the software were compared with each other. WITNESS 2004 Manufacturing Edition can present bar charts for each report while ARENA 13 does not have this feature. On another aspect, ARENA 13 is able to classify the activities under one or more specific groups but WITNESS 2004 Manufacturing Edition does not offer this feature.

[16]

[17]

[18]

[19] [20]

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