Research Journal of Applied Sciences, Engineering and Technology 4(18): 3267-3273, 2012
ISSN: 2040-7467
© Maxwell Scientific Organization, 2012
Submitted: December 30, 2011 Accepted: January 25, 2012 Published: September 15, 2012
1
1
2
1
1
2
Abstract: In this study, the application of project scheduling for analysis and evaluation of mechanized greenhouse construction project was studied using Critical Path Method (CPM) with WinQsb software. This study was conducted in Khuzestan province of Iran. The results showed that the minimum completion time of this project, based on using CPM method, normal time and crash time is 201 and 137 days, respectively.
Normal cost and crash cost are 3102665000 and 3187740000 Rials, respectively. Also cost slope in CPM method is 1329300 Rials that it means cost of reducing one day of the project completion time is 1329300 Rials.
So results of CPM method showed that the cost of reducing the project completion time, to 180 days is 1600000
Rials.
Keywords: CPM method, mechanized greenhouse construction, project scheduling
INTRODUCTION
Careful planning is important before a greenhouse project is started. Building a greenhouse need to be expensive and time-consuming. Primary cost of greenhouse construction is high, so project scheduling is importance for management of these units construction.
Basic project scheduling: Schedule planning and control are major tasks of construction project management
(Yang, 2007). Traditional scheduling techniques, such as
Critical Path Method (CPM), have been widely applied for several decades (Foulds and Wilson, 2005). This model has been used extensively to calculate operation parameters, including: earliest starting time, latest starting time, earliest completion time, latest completion time, maximum available time and float time (Zargar, 2004).
However, schedule delays often occur in many of these construction projects. Effective project management techniques are important to ensure successful project performance; a poor strategy can easily turn expected profit into loss (Abdallah et al.
, 2009). The management of construction project involves planning of tasks from large numbers of disciplines which require different pieces of information at various times. This results in the production of a huge quantity of complex information, which must be managed efficiently. Network analysis provides a comprehensive practical system for planning and controlling large projects in construction and many other fields. Network is a graphical representation of a project. Network analysis provides a practical way to monitor the progress of the project till its accomplishment in the minimum time; it can also be used to assist in allocating resources and to minimize total cost (Chen and
Huang, 2007). The solution of network models is accomplished through a variety of network optimization algorithms. One of them is CPM.
Critical path method (CPM): CPM was developed by
Du Pont and the emphasis was on the trade-off between the cost of the project and its overall completion time
(e.g., for certain activities it may be possible to decrease their completion times by spending more money)
(Sabzehparvar, 2008). CPM models are extremely useful for the purpose of planning, analyzing, controlling the progress and the completion of large and complex projects
(Paul, 1978). The purpose of CPM is to identify critical activities on the critical path so that resources may be concentrated on these activities in order to reduce project length time (Burke, 2003). Besides, CPM has proved very valuable in evaluating project performance and identifying bottlenecks.
In this study, the application of project scheduling for analysis and evaluation of mechanized greenhouse construction project was studied using CPM methods with
WinQsb software. This study was conducted in Khuzestan province of Iran.
MATERIALS AND METHODS
Data were collected from variety sources such as reports and statistics of agricultural organization, opinions
Corresponding Author: Nasim Monjezi, Department of Agricultural Machinery,
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Res. J. Appl. Sci. Eng. Technol., 4(18): 3267-3273, 2012
Table 1: The activities list of project scheduling of mechanized greenhouse construction (classic CPM network)
Activity description
Immediate predecessor
----------------------------------
Activity code Immediate predecessor Normal Crash
Cost (1000 rials)
------------------------------------------
Crash Normal
Start
Land supply
Soil and water tests and analysis
Preparing of plans and maps
Getting greenhouse establishment license
S
1
2
3
4
Land excavation and leveling
Construct of wall and fencing
Raw material storage building
Greenhouse building
Office affairs building
5
6
7
Guarding building
Engine room building
Layout of lines and roads
Electrification (membership
fee, installation of transformers and cabling and wiring)
Power generator
Water supply (pump,
plumbing, etc.)
Gas supply (membership fee and gas pipe, etc.)
14
15
16
Membership fee for telephone 17
Fuel tank 18
Water reservoir
Heating establishments
19
20
21 Cooling establishments
(fan and pad)
Weighing machine
Fire equipment (2
22
23
8
9
10
11
12
13 capsules Fire)
Greenhouse electrical system(window and canopy electromotor )
24
Fogging and spraying nozzle systems
Thermometer and humidity gauge
CO
2
production system
Greenhouse canopy
24
26
27
28
Greenhouse monitoring panels 29
Greenhouse irrigation 30 equipment
Office equipment (desks,
chairs, files, phone, etc.)
Gardening tools (wheel-
31
Chemical fertilizer and farmyard manure supply
32 barrow, sprayer, etc.)
Pesticide and fungicide supply 33
34
35 Plastic pots and plastic boxes supply
Seed supply
Diesel fuel and gasoline
36
37 provide
Oil supply
Getting production and utilization license
End
38
39
E
-
S
1
1
2, 3
4
5
6
6
6
6
6
7, 8, 9, 10, 11
12
13
12
12
12
11
15
8
8
7
7, 9
13
8
8
8
8
20, 21, 24, 26
8
9
7
7
7
7
7
18
7
12, 18, 19, 20, 21
39
0
14
7
45
40
7
7
30
45
30
25
30
14
15
5
7
7
5
7
7
7
7
1
2
4
7
3
5
5
5
5
2
3
1
5
1
1
2
2
15
0
0
7
5
30
30
5
5
20
30
20
15
20
10
10
3
5
5
3
5
5
5
5
1
1
2
5
2
3
3
3
3
1
2
1
3
1
1
1
1
10
0
0
202500
1200
17500
1500
1200
59400
30000
1453000
3200
15000
30000
72000
70500
17000
65000
7400
2200
2700
64000
137000
106500
6000
200
42000
105500
3000
12500
217500
90300
44000
15000
11500
18900
11120
198000
17920
32500
1500
1500
0
0
200000
1000
16000
1000
1000
54000
28000
1418000
3000
14000
28000
66000
67500
17000
60000
6600
2000
2500
62500
135000
105000
6000
200
39600
105000
3000
12000
210000
88825
42500
15000
11500
18900
11120
198000
17920
32500
1500
1000
0
3268

Res. J. Appl. Sci. Eng. Technol., 4(18): 3267-3273, 2012 and comments of agricultural experts and advocators, contractors, consulting engineers and farmers. The collected data belonged to the 2010/11 year.
CPM is a vital tool for the planning and control of complex projects (Yao and Lin, 2000) . In this method, time of each activity is deterministic (Fahimifard and
Kehkha, 2009; Moder, 1988). These times are shown in
Table 1. All times are given in day. To identify the critical path, three parameters for each of its activities are determined:
C Earliest event time
C
Latest event time
C Slack time
Paths other than the critical path offer flexibility in scheduling because they take less time to complete less than the critical path. The program’s activities are either critical or non-critical. An activity is critical if a delay in its implementation delays project completion; while an activity is non-critical if the schedule shows that the difference between its latest completion date and its earliest start date is greater than the duration of the activity. In this latter case, the non-critical activity is considered as having slack or a degree of flexibility. The critical path is reached through two phases (Algarra and
Argilaga, 2005; Lu and AbouRizk, 2000):
Forward pass calculation: The first, which is prospective "forwards", runs from the first to the last node in the network and allows the operator to determine the earliest occurrence for each event, which is represented by
ES i
. The notation for the action (i, j) would be (Fig. 1): where, i represents the event that precedes the activity (i, j), j the event that follows the activity (i, j) and d ij
its duration.
If ES i
is the earliest occurrence of event i and ES j
is the earliest occurrence of event j, the calculations for the prospective phase are:
C Where, i = 1, the first node in the network is ES
C
For the remaining nodes in the network ES i
= 0 j
= max
[Es i
+ d ij
]
For all the arcs that begin at node i and terminate at node j. Thus, the procedure adopted in making the calculation ensures that when determining the earliest occurrence of event j, the earliest dates previously calculated for the events and directly preceding the j node are taken into account. These are known as early values.
The results of calculation are shown in Table 2.
Bacwarkward passing processing: The second, which is retrospective "backward", begins from the end node and works back to the network’s first node, allowing the operator to determine the latest occurrence for each event in the network, which is represented by LF i
. If LF i
is the
Fig.1: Notation given to events and activity latest occurrence of event i and LF j
is the latest occurrence of event j. The calculations for the retrospective phase are based on the ES n value found for i = n, or the terminal node in the network. From the terminal node one can then proceed towards the first node, using the following rules:
C LF n
= ES n
for the terminal node in the network
(Malcolm et al.
, 1959)
C
For the remaining nodes in the network:LF i
= min
[LF j
d ij
]
For all the arcs that begin at node i and terminate at node j. Thus, the procedure adopted in making the calculation ensures that when determining the latest occurrence of event i, all the j nodes coming after the i node are taken into account. These are known as last values. The results of calculation are shown in Table 2.
Having completed both phases of the calculation, the critical path activities can be easily identified. A project’s critical path is understood to mean that sequence of critical activities which connects the project’s start event to its end event cannot be delayed without delaying the project (Abdi et al.
, 2010). An activity (i, j) will belong to the critical path if it satisfies the following three conditions:
C ES
C
ES
C
ES j i
= LF j
= LF
!
ES i j i
= LF j
!
LF i
= d ij
This implies that there is no slack in the first or the last events of the activity (conditions 1 and 2) or in the activity itself (condition 3), which means the activity is critical.
Slack calculation: Difference between the latest time and the earliest time of an activity is the slack time for that activity. Slack is the amount of time an activity can be delayed without delaying the project completion
(Hajshirmohammadi, 2009). Slack times were calculated as:
(1) S = LS - ES = LF – EF
The results of calculation are shown in Table 2.
Minimum cost technique: In many programs, having access to all the resources required in order to optimize
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Res. J. Appl. Sci. Eng. Technol., 4(18): 3267-3273, 2012
Table 2: Computation results of project CPM network with normal and crash time
Activity code
Immediate predecess or
Crash time Normal time
--------------------------------------------------------------------------------------------------------------------------------
Earliest Latest Earliest Latest starts starts finishs finishs Slack
Earliest start Latest start Earliest Latest finish Slack finishs
14
15
16
17
18
19
20
9
10
11
12
13
4
5
6
7
8
2
3
S
1
-
S
1
1
2, 3
4
5
6
6
6
6
6
7, 8, 9, 10, 11
12
13
12
12
12
11
15
8
26
27
28
29
30
21
22
23
24
25
8
7
7, 9
13
8
8
8
8
20, 21, 24, 26
8
107
107
107
129
107
107
97
97
127
107
31
32
33
34
35
36
37
9
7
7
7
7
7
18
97
97
97
97
97
97
102
38
39
E
7
39
Project comple 137 tion time (day)
97
12, 18, 19, 20, 21 127
137
Total cost of project (rials)
3187740000
Project cost on 1937600000 critical path (rials)
Number of 2 critical path (s)
Critical path # 1 E-39-19-15-12-8-6-5-4-3-2-1-S
Critical path # 2 E-39-12-8-6-5-4-3-1-S
136
135
136
134
136
136
136
136
127
137
132
134
134
134
134
122
136
136
132
132
127
117
117
117
97
122
107
77
77
77
107
117
37
67
72
77
77
7
7
0
0
134
117
132
134
122
122
122
87
92
87
107
122
37
67
72
87
77
0
0
32
7
130
122
122
120
102
127
112
97
92
97
117
127
0
7
12
37
67
72
77
97
107
109
110
110
132
110
112
98
98
129
112
98
99
98
100
98
98
103
98
137
137
137
122
137
137
127
127
127
107
107
107
117
132
0
7
37
37
37
72
77
107
107
134
137
137
137
137
127
137
137
134
137
137
137
137
137
137
137
137
137
137
137
7
0
15
17
25
0
15
0
5
10
15
10
0
0
0
10
0
0
0
25
0
5
5
25
27
27
15
39
39
5
25
39
38
39
37
39
39
34
39
0
0
187
172
172
172
143
179
158
113
113
113
158
172
0
0
14
14
59
99
106
113
113
158
158
158
191
158
158
143
143
187
158
143
143
143
143
143
143
150
143
186
201
201
3102665000
1879500000
2
196
172
194
196
179
179
179
128
133
128
158
177
0
0
52
14
59
99
106
128
113
193
196
196
196
196
179
200
199
192
194
199
198
200
196
200
200
199
199
186
201
E-39-19-15-12-8-6-5-4-3-1-S
E-39-12-8-6-5-4-3-1-S
0
14
21
59
99
106
113
143
158
143
138
143
172
187
192
179
179
201
179
201
177
150
201
186
186 186
165 186
158
158
158
172
192
0
14
59
59
99
106
113
158
158
145
146
144
148
144
144
145
145
201
201
161
163
163
196
163
165 186
144 201
145 201
191
165
196
201
196
201
201
201
201
201
201
201
201
201
201
201
201
201
201
9
0
22
24
36
0
21
0
5
15
20
15
0
0
0
15
0
0
0
38
0
35
38
38
5
38
21
57
56
5
36
56
55
57
53
57
57
56
56
0
0 the plan is unthinkable. On the contrary and given the objectives of many programs, a schedule of program actions has to be chosen that ensures the minimization of costs. CPM is the best known minimum cost technique and was originally designed to consider the minimization of project costs under a series of initial hypotheses. The difficult part of the technique is to determine the activity or combination of activities whose duration should be reduced by one unit, so that total costs can be minimum for this duration. To be able to do this, the cost slope must first be known, that is the absolute value of the slope of the cost-duration function of each activity, which is made operative using the following formula (Algarra and
Argilaga, 2005; Chizari and Amirnejad, 1998): cos t slope

C f

C n
D n

D f
(2) where, C f
is the crash cost,C normal time and D f n
is the normal cost,D n
is the
is the crash time. The results are shown in Table 4. Consequently, the smaller increment in
3270

Res. J. Appl. Sci. Eng. Technol., 4(18): 3267-3273, 2012
Fig. 2: Mechanized greenhouse construction project CPM network model costs will lead to a one time unit reduction in the duration of the activity or combination of activities with the lower cost slope, which reduces the duration of the program by one time unit. The technique can be applied until it is impossible to reduce the overall duration anymore because of the existence of a critical path with all its activities with a record duration.
time. In addition, the Table 2 shows that the minimum project completion times using normal time and crash time are 201 and 137 days, respectively. In addition to total cost of project using normal time and crash time are
3102665000 and 3187740000 Rials.
RESULTS AND DISCUSSION
Using the data contained within Table 1, mechanized greenhouse construction project CPM network has been drawn in the shape of an arrow network (Fig. 2). Critical path, events and activities are known and represented in the network with lines (Fig. 2). Critical paths are represented in the network with red thick lines (Fig. 2).
CPM analysis: For the project with deterministic activity times, crashing analysis is a process of reducing the activity time to meet the desired completion time. The results of crashing analysis for project scheduling (normal time, crash time, suggested time, additional cost, suggested cost and total cost of reducing the project completion time to 180 days) by using of WinQsb software, have been shown in Table 3. The Table 3 shows that, the cost of reducing the project completion time to
180 days is 1600000 Rials.
Minimum project completion time (using normal time and crash time): The results of activity analysis for project scheduling (minimum project completion time, critical activities, earliest and latest start time, earliest and latest finish time and slack time) of mechanized greenhouse construction project, by using WinQsb software and based on using normal time and crash time, have been shown in Table 2.
The Table 2 shows that, there are 2 critical paths and the activities 1, 3, 4, 5, 6, 8, 12, 15, 19 and 39, respectively are critical. In this means that, delays in their commencement will delay the overall project completion
Cost slop: Normal time, crash time, normal cost and crash cost for each activity are shown in Table 1. For cost slope calculation, difference of crash and normal cost and difference of crash and normal time are shown in Table 4.
At last, cost slope is calculated for each activity by formula No. 2 and it is presented in Table 4. For example, according to Table 1 normal cost and crash cost, normal time and crash time of activity No. 2 are 1000000 and
1200000 Rials, 7 and 5 days, respectively that difference of crash and normal cost and difference of crash and normal time are 200000 Rials and 2 days, respectively. As a result, cost slope is calculated 100000 that it means cost
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Res. J. Appl. Sci. Eng. Technol., 4(18): 3267-3273, 2012
Table 3: Crashing analysis for project completion in 180 day
Activity code
S
9
10
11
12
13
14
15
7
8
5
6
3
4
1
2
24
25
26
27
28
29
30
20
21
22
23
16
17
18
19
35
36
37
38
31
32
33
34
39
E
Overall project -
15
0
2
2
1
1
1
5
2
3
5
5
5
3
5
4
7
1
2
7
7
7
7
7
5
Normal time
0
30
25
30
14
15
5
7
7
7
30
45
14
7
45
40
1
1
1
1
1
3
1
5
10
0
-
3
3
3
2
3
2
5
1
1
5
5
5
5
5
3
Crash time
0
20
15
20
10
10
3
5
5
5
20
30
7
5
30
30
2
2
1
1
1
5
2
3
15
0
180
5
5
5
3
5
4
7
1
2
7
7
7
7
7
5
Suggested time
0
30
25
30
14
15
5
7
7
7
30
45
14
7
34
30
0
0
0
0
0
0
0
0
0
0
1600
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Additional cost
(Thousand Rials)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1100
500
15000
11500
18900
11120
198000
17920
32500
1500
1000
0
3102665
6600
6600
2500
62500
135000
105000
6000
200
39600
105000
3000
12000
210000
88825
42500
Normal cost
(1000 Rials)
0
200000
1000
16000
1000
1000
54000
28000
1418000
3000
14000
28000
66000
37500
17000
60000
15000
11500
18900
11120
198000
17920
32500
1500
1000
0
3104265
6600
6600
2500
62500
135000
105000
6000
200
39600
105000
3000
12000
210000
88825
42500
Suggested cost cost (1000 Rials)
0
200000
1000
17100
1500
1000
54000
28000
1418000
3000
14000
28000
66000
67500
17000
60000
9
10
11
12
7
8
5
6
2
3
S
1
4
13
14
Table 4: Computation results of quantity time reduction (day) and cost of one unit time reduction (1000 Rials) for each of activities
Difference of Difference of crash and normal crash and normal
Activity code time (C f
!
C n
) time (D n
!
D f
) Cost slope Activity code
Difference of Difference of crash and normal crash and normal time (C f
!
C n
) time (D n
!
D f
)
0
2500
200
1500
500
200
5400
2000
35000
200
1000
2000
6000
3000
0
5
2
10
10
10
4
5
2
10
15
0
7
2
15
10
0
357.14
100
100
50
100
2700
200
2333.33
20
100
200
1500
600
0
24
25
26
27
20
21
22
23
15
16
17
18
19
27
28
5000
800
200
200
1500
0
0
2000
1500
2400
500
0
500
500
7500
1
1
2
2
0
1
2
2
1
2
2
2
2
2
2
Cost slope
2500
400
100
100
750
0
0
1000
750
1200
250
0
250
250
3750
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Res. J. Appl. Sci. Eng. Technol., 4(18): 3267-3273, 2012
Table 4: (Continue)
29
30
31
32
33
34
Difference of Difference of crash and normal crash and normal
Activity code time (C f
!
C n
) time (D n
!
D f
)
0
0
0
0
1475
1500
1
1
2
2
0
2
Cost slope
0
0
0
0
737.50
750
Activity code
35
36
37
38
39
E
Difference of Difference of crash and normal crash and normal time (C f
!
C n
) time (D n
!
D f
)
0
0
0
0
500
0
1
1
0
0
5
0
Cost slope
0
0
0
0
100
0 of reducing one day of activity No. 2 time is 100000
Rials.
CONCLUSION
Schedule planning and control are major tasks of construction project management. In this paper, the application of project scheduling for analysis and evaluation of mechanized greenhouse construction project was studied using CPM methods with WinQsb software.
Critical activities and paths were determined. The results showed that minimum completion time of this project, base on using normal time and crash time CPM method is
201 and 137 days, respectively. Also results of CPM method showed that the cost of reducing the project completion time of this project, to 180 days is 1600000
Rials.
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