116906.attach

Report
Project Scheduling: Lagging,
Crashing, and Activity
Networks
10-01
Chapter 10 Learning Objectives
After completing this chapter, students will be able to:
 Apply lag relationships to project activities.
 Construct and comprehend Gantt charts.
 Recognize alternative means to accelerate projects,
including their benefits and drawbacks.
 Understand the trade-offs required in the decision to crash
project activities.
 Develop activity networks using Activity-on-Arrow
techniques.
 Understand the differences in AON and AOA and
recognize the advantages and disadvantages of each
technique.
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
10-02
Lags in Precedence Relationships
The logical relationship between the start and
finish of one activity and the start and finish of
another activity.
Four logical relationships between tasks
1. Finish to Start
2. Finish to Finish
3. Start to Start
4. Start to Finish
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10-03
Finish to Start Lag
Most common type of sequencing
Shown on the line joining the modes
 Added during forward pass
 Subtracted during backward pass
0
A
6
Spec Design
6
6
B
11
Design Check
5
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Lag 4
15
C
22
Blueprinting
7
10-04
Finish to Finish Lag
Two activities share a similar completion point
 The mechanical inspection cannot happen until wiring,
plumbing, and HVAC installation are complete
15
D
Wiring
6
21
10
A
16
Plumbing
6
Lag 3
16
B
HVAC
5
21
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21
C
22
Inspection
1
10-05
Start to Start Lag
30
D
Wiring
6
36
Lag 3
31
A
33
Plumbing
6
33
B
HVAC
5
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36
36
C
37
Inspection
1
10-06
Start to Finish Lag
Least common type of lag relationship
Successor’s finish dependent on
predecessor’s start
30
D
Wiring
6
36
22
A
28
Plumbing
6
Lag 3
28
B
HVAC
5
33
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33
C
34
Inspection
1
10-07
Gantt Charts
 Establish a time-phased network
 Can be used as a tracking tool
Benefits of Gantt charts
1. Easy to create and comprehend
2. Identify the schedule baseline network
3. Allow for updating and control
4. Identify resource needs
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10-08
Completed Gantt Chart for Project Delta
FIGURE 10.8
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10-9
Gantt Chart for Project Delta with
Critical Path Highlighted
FIGURE 10.9
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10-10
Gantt Chart with Resources Specified
FIGURE 10.10
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10-11
Gantt Chart with Lag Relationships
FIGURE 10.11
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10-12
Crashing
The process of accelerating a project
Principal methods for crashing
Improving existing resources’ productivity
Changing work methods
Compromise quality and/or reduce project scope
Institute fast-tracking
Work overtime
Increasing the quantity of resources
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10-13
Managerial Considerations
 Determine activity fixed and variable costs
 The crash point is the fully expedited activity
 Optimize time-cost tradeoffs
 Shorten activities on the critical path
 Cease crashing when
 the target completion time is reached
 the crashing cost exceeds the penalty cost
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10-14
Project Activities and Costs
Normal
Crashed
Activity
Duration
A
5 days
$ 1,000
3 days
$ 1,500
B
7 days
700
6 days
1,000
C
3 days
2,500
2 days
4,000
D
5 days
1,500
5 days
1,500
E
9 days
3,750
6 days
9,000
F
4 days
1,600
3 days
2,500
G
6 days
2,400
4 days
3,000
H
8 days
9,000
5 days
15,000
Total costs 
Cost
$22,450
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Duration
Cost
$37,500
Table 10.1
10-15
FIGURE 10.14 Time–Cost Trade-Offs for Crashing Activities
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10-16
FIGURE 10.15 Fully Crashed Project Activity Network
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10-17
FIGURE 10.16 Relationship Between Cost and Days Saved in a Crashed Project
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10-18
Activity on Arrow Networks
 Activities represented by arrows
 Widely used in construction
 Event nodes easy to flag
 Forward and backward pass logic similar to AON
 Two activities may not begin and end at common
nodes
 Dummy activities may be required
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10-19
Notation for Activity-on-Arrow (AOA)
Networks
FIGURE 10.18
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10-20
Sample Network Diagram Using AOA
Approach
FIGURE 10.19
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10-21
Representing Activities with Two or More
Immediate Successors(Wrong)
FIGURE 10.20A
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10-22
Alternative Way to Represent Activities
with Two or More Immediate Successors
(Wrong)
FIGURE 10.20B
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10-23
Representing Activities with Two or More
Immediate Successors Using Dummy
Activities (Better)
FIGURE 10.20C
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10-24
Partial Project Delta Network Using AOA
Notation
FIGURE 10.21
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10-25
Completed Project Delta AOA Network
FIGURE 10.22
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10-26
Project Delta Forward Pass Using AOA
Network
FIGURE 10.23
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10-27
Project Delta Backward Pass Using AOA
Network
FIGURE 10.24
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10-28
Controversies in the Use of Networks
Networks can be too complex
Poor network construction creates problems
Networks may be used inappropriately
When employing subcontractors
 The master network must be available to them
 All sub-networks must use common methods
Positive bias exists in PERT networks
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
10-29
Summary
1.
2.
3.
4.
5.
6.
Apply lag relationships to project activities.
Construct and comprehend Gantt charts.
Recognize alternative means to accelerate projects,
including their benefits and drawbacks.
Understand the trade-offs required in the decision to
crash project activities.
Develop activity networks using Activity-on-Arrow
techniques.
Understand the differences in AON and AOA and
recognize the advantages and disadvantages of each
technique.
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
10-30
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
10-31

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