Civil Engineering Reference
In-Depth Information
Example 11.2
Draw the network for the following project.
Duration (Days)
Activity
IPA
Optimistic (
To
)
Most Likely (
Tm
)
Pessimistic (
Tp
)
A
-
4
5
6
B
A
10
12
14
C
A
7
9
16
D
B
14
17
22
E
B, C
10
15
30
F
C
4
7
13
G
D
12
20
40
H
D, E
10
12
15
I
F, H
8
9
10
Compare the three paths: ABDHI, ABDG, and ABEHI. Calculate the
expected duration and standard deviation for each path. Considering all three
paths, what is the duration of the project with at least a 95% confidence?
Solution
With regular CPM calculations (using most likely durations), the critical path is
ABDHI with 55 days, followed by paths ABDG and ABEHI at 54 and 53 days,
respectively (Figure 11.10). Now, let's do PERT calculations.
Duration
Variance
(
V
e
=σ
e
)
Activity Optimistic
(
To
)
Most
Likely (
Tm
)
Pessimistic
(
Tp
)
Expected
Duration (
Te
)
Standard
Deviation (
σ
e
)
A
4
5
6
5
.
00
0.33
0
.
11
B
10
12
14
12
.
00
0.67
0
.
44
C
13
9
16
9
.
83
1.50
2
.
25
D
20
17
22
17
.
33
1.33
1
.
78
E
10
15
30
16
.
67
3.33
11
.
11
F
4
7
13
7
.
50
1.50
2
.
25
G
12
20
40
22
.
00
4.67
21
.
78
H
10
12
15
12
.
17
0.83
0
.
69
I
8
9
10
9
.
00
0.33
0
.
11
With regard to path ABDHI,
T
E
=
5
.
00
+
12
.
00
+
17
.
33
+
12
.
17
+
9
.
00
=
55
.
50 days
V
E
=
0
.
11
+
0
.
44
+
1
.
78
+
0
.
69
+
0
.
11
=
3
.
14
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