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3 Examples and practice 154

3 Examples and practice 154

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Developing the (single-project) critical chain plan

155

Critical chain

1.1 (15)

1.2 (10)
3 (15)

2.1 (10)

2.2 (5)

PB-20

FB
40 days
60 days

Figure 6.3

With no resource contention, just add buffers.

1
Red

15 days

2.1
3
Blue

3

1.2

1.1

2
Green

10 days

5
15 days
Magenta

2.2
10 days

Figure 6.4
(colors).

4
Green

5 days

The same projects with specific resource assignments

We lay the network out, with all the tasks pushed as late as possible.
In this case, all we have to do is add a start-as-late-as-possible constraint
to task 2.1 (Figure 6.5).
Next, remove the resource conflict, working backward from the end
of the project.
Figure 6.6 illustrates the two ways we could resolve the green
resource contention. Note that each schedule shows a new dependency
for the resource constraint. Which resolution choice is better? You may
initially think that the lower choice is better, because it is a shorter
schedule. With the lower choice, the two chains are the same length, so
we could choose either one as the critical chain. Add the project buffer
and CCFB to each option and see what happens (Figure 6.7).

156

ID
1
2
3
5

Figure 6.5

1.2

10 days

2.1

10 days

2.2

5 days

3

S

Jan 16, '00
Jan 23, '00
M W F S T T

S

Jan 30, '00
Feb 6, '00
M W F S T T

S

Green
Blue

15 days

The first step pushes tasks to the late finish.

Green
Magenta

Critical Chain Project Management

4

Jan 2, '00
Jan 9, '00
Task name Duration S M W F S T T
15 days Red
1.1

2
3
4
5

Jan 2, '00
Jan 9, '00
Task name Duration S M W F S T T
15 days Red
1.1
10 days
1.2
2.1

10 days

2.2

5 days

3

15 days

1.1

15 days

1.2

10 days

2.1

10 days

S

Jan 16, '00
Jan 23, '00
M W F S T T

S

Jan 30, '00
Feb 6, '00
M W F S T T

Green
Blue
Green
Magenta

6
7
8
9
10
11

3

5 days

Green
Blue
Green

15 days

Alternative ways to resolve resource conflict.

Magenta

157

Figure 6.6

2.2

Red

S

Developing the (single-project) critical chain plan

ID
1

158

ID
1
2
3
4

6
7

Figure 6.7

1.1

'99
S

W

Jan 9, '00
S
T
M

Jan 23, '00
T
S

W

Feb 6, '00
S
T
M

F

Feb 20, '00
T
S

W

Mar 5, '00
S
T
M

Red
Green

1.2
2.1

F

Blue

FB
2.2
3

Green

Magenta

PB

The first choice results in a planned completion date of March 7, 2000.

Critical Chain Project Management

5

Task name

Developing the (single-project) critical chain plan

159

Figure 6.8 illustrates the critical chain plan for the first choice of
removing conflict for the green resource. The critical chain comprises
all the project tasks except task 2.1. The buffers are sized as 50% of the
feeding chains. (In a case like this, we recommend a modification of
that later for the feeding buffer.)
The two choices of critical chain from the first resource resolution
option both lead to the same overall length of schedule. Both also create
the situation in which the noncritical chain is longer than the critical
chain after the addition of the feeding buffer. That is all right; we just have
the extra lead time for the noncritical chain paths. That often happens
when a schedule starts with two or more paths of nearly equal length. If
you are not comfortable with this method, you may move the excess
feeding buffer (i.e., the amount that would push the non-critical chain
earlier than the critical chain) to just in front of the project buffer. When
you use buffer management, act as if all the feeding buffers were together
at the end of the feeding chain.
Any of those paths is suitable for the plan because the differences are
small compared to the project buffer. It often works out a little better to
resolve contention by moving the longer of the two or more tasks backward in time. That tends to keep the critical chain the longest chain, thereby
increasing the project buffer and adding to the immunity of your project.
Lay out the exercise as a critical chain plan, with all the appropriate
buffers. In Figure 6.9, the first line in each box represents the task
number. The second line represents the resource, by color. The third line
represents the (already reduced) task time, in days. (See the last question
in Section 6.10 for the approximate length of the schedule you should
have obtained. Note that a good enough schedule is within a small part of
the project buffer of the schedule given in the back of the book.)
6.3.2

Large example

Figure 6.10 presents the task network for the large example. The top line
of each box is the identifier for the task; the color relates to a specific
resource; and the number at the bottom of each box represents the task
duration, in days. The task durations have already been cut by 50%. Lay
out the critical chain plan for this project.
The first step is to lay out the late-finish sequence of tasks. To do that,
you have to convert the network plan to tasks that give the planned
duration. Figure 6.11 shows the project laid out with Microsoft Project 98

160

Jan 2, '00
Jan 9, '00
ID Task name Duration S M W F S T T
1 1.1
15 days
Red
2 1.2
10 days
3

2.1

10 days

4

2.2

5 days

5

FB

8 days

6

3

15 days

7

PB

22 days

9

1.1

15 days

10

FB

8 days

Jan 16, '00
Jan 23, '00
Jan 30, '00
Feb 6, '00
S M W F S T T S M W F S T T

Feb 13, '00 Feb 20, '00 Feb 27, '00 Mar 5, '00
S M W F S T T S M W F S T T

S

M

Green

Blue
Green
Magenta

8

1.2

10 days

2.1

10 days

13

2.2

14

3

15 days

15

PB

22 days

5 days

Green
Blue
Green
Magenta

Figure 6.8 The second resource resolution choice leads to the same lead time for the two choices of critical
chain and completion on March 10, 2000.

Critical Chain Project Management

11
12

Red

Developing the (single-project) critical chain plan
A-2
Red
15

A-4
Green
10

C-2
Blue
15

C-4
Green
5

E-2
Blue
15

E-4
Green
5

G-2
Red
15

G-4
Blue
15

Figure 6.9

A-1
Magenta
5

161

B-6
Magenta
10

Project
complete

F-6
Magenta
5

Small exercise.

A-2
Black
10

A-3
Green
15

A-4
Red
10

B-2
Magenta
10

B-3
Blue
10

B-4
Red
5

C-3
Blue
15

C-4
Green
10

D-3
Blue
20

D-4
Green
5

Figure 6.10

A-5
Magenta
20

A-6
Red
15

C-5
Red
15

C-6
Magenta
5

Project
complete

Large example. (Task times already reduced.)

using the as-late-as-possible constraint. The calendar is set to work
through the weekends.
Work from the end of the project forward in time to remove the
resource contention. The first conflict is between two tasks using red, A-6
and C-5. Because the A path is the critical path, it usually makes sense to
give it the resource first, which means moving the A path forward in
time, and the B path along with it, as illustrated on the following page.
Figure 6.12 shows the plan with the contention removed.

162

ID
1

Task
name
A-1

August
September
October
Duration Predec. 4 7 10 13 16 19 22 25 28 31 3 6 9 12 15 18 21 24 27 30 3 6 9 12 15 18 21 24 27 30
5 days
Mag

A-2

10 days 1

A-3

15 days 2

4

A-4

10 days 3

5

A-5

20 days 4,9

6

A-6

15 days 5

7

B-2

10 days

8

B-3

10 days 7

9

B-4

5 days 8

10

C-3

15 days

11

C-4

10 days 10

12

C-5

15 days 11,15

13

C-6

14

D-3

15

D-4

5 days 14

16

Comp.

0 days 6,13

Figure 6.11

Black
Green
Red
Magenta
Red
Magenta
Blue
Red
Blue
Green
Red

5 days 12
20 days

Mag
Blue

Large example time-scaled logic illustrates resource contention.

Green

10/19

Critical Chain Project Management

2
3

i

Task
name
A-1
A-2
A-3
A-4
A-5
A-6
B-2
B-3
B-4
C-3
C-4
C-5
C-6
D-3
D-4
Comp.

Resolving the initial (A6-C5) red-resource contention.

163

Figure 6.12

August
September
October
November
Duration Prede. 4 7 10 13 16 19 22 25 28 31 3 6 9 12 15 18 21 24 27 30 3 6 9 12 15 18 21 24 27 30 2 5 8 11 14
5 days
Mag
10 days 1
Black
15 days 2
Green
10 days 3
Red
20 days 4,9
Magenta
15 days 5
Red
10 days
Magenta
10 days 7
Blue
5 days 8
Red
15 days
Blue
10 days 10
Green
15 days 11,15,6
Red
5 days 12
Mag
20 days
Blue
5 days 14
Green
11/10
0 days 6,13

Developing the (single-project) critical chain plan

ID
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

164

Critical Chain Project Management

The next conflict is green (C4 and D4), followed by blue (C3 and D3).
Because those paths and tasks will not be on the critical chain, and both
are the same length, the order is somewhat arbitrary. You then have to
remove the red conflict (A-4 and B-4), and so on. This first round of
conflict removal leads to the project plan shown in Figure 6.13.
You can now select the critical chain and size the project buffer. The
critical chain comprises tasks A-1, A-2, A-3, A-4, B-4, A-5, A-6, C-5, and
C-6, which add up to 100 days. We should set the project buffer size as
50 days, for an overall planned lead time of 150 days for the project.
Next, you have to add the CCFBs. The tasks that feed the critical chain
are B-4, C-4, and D-4. Working backward, we can add the feeding buffer
for D-4 (22 days). That creates some new conflicts. C-4 requires a 22-day
feeding buffer also. We have to do D-4 before we do C-4, so if D-4 is late, it
will show up in the buffer from C-4.
The final step is to add the resource buffers. (We could have added
them immediately after identifying the critical chain but did not, simply
to keep the chart clearer until we were done.) The final plan (Figure 6.14)
shows the resource buffers as boxed Rs. The buffer goes with the task
immediately above it.
This completes the feasible and immune plan.
6.3.3

Large exercise

Lay out the exercise in Figure 6.15 as a critical chain plan, with all the
appropriate buffers. As in the small exercise, the first line in each box
represents the task number. The second line represents the resource, by
color. The third line represents the (already reduced) task time, in days.
(See the last questions in Section 6.10 for the approximate length of the
schedule you should have obtained.) Note that a good enough schedule
is within a small part of the project buffer of the schedule given in
Section 6.10. You can find a picture of the completed plan on Advancedprojects.com.

6.4

Buffer and threshold sizing

Buffer sizing determines the overall duration of your project and the
degree of overall contingency included in the plan. The buffer thresholds
for action determine the frequency with which you will act. We usually

Task
name
A-1
A-2
A-3
A-4
A-5
A-6
B-2
B-3
B-4
C-3
C-4
C-5
C-6
D-3
D-4
Comp.

Resolving other resource contentions.

165

Figure 6.13

August
September
October
November
Duration Pred. 4 7 10 13 16 19 22 25 28 31 3 6 9 12 15 18 21 24 27 30 3 6 9 12 15 18 21 24 27 30 2 5 8 11 14 17 20 23 26 29
5 days
Mag
10 days 1
Black
15 days 2
Green
10 days 3
Red
20 days 4,9
Magenta
15 days 5
Red
10 days
Magenta
10 days 7
Blue
5 days 8,4
Red
15 days 8
Blue
10 days 10
Green
15 days 11,15,6
Red
5 days 12
Mag
20 days
Blue
5 days 14
Green
11/15
0 days 13

Developing the (single-project) critical chain plan

ID
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16