Project Management Ch10

Chapter 10
Project Scheduling: Lagging,
Crashing, and Activity
Networks
10-01

Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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.
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
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
10-04
0 A 6
Spec Design
6
6 B 11
Design Check
5
15 C 22
Blueprinting
7
Lag 4

Finish to Finish Lag
Two activities share a similar completion point
– The mechanical inspection cannot happen until
wiring, plumbing, and HVAC installation are
complete
10-05
10 A 16
Plumbing
6
16 B 21
HVAC
5
21 C 22
Inspection
1
15 D 21
Wiring
6
Lag 3

Start to Start Lag
10-06
31 A 33
Plumbing
6
33 B 36
HVAC
5
36 C 37
Inspection
1
30 D 36
Wiring
6
Lag 3

Start to Finish Lag
• Least common type of lag
relationship
• Successor’s finish dependent on
predecessor’s start
10-07
22 A 28
Plumbing
6
28 B 33
HVAC
5
33 C 34
Inspection
1
30 D 36
Wiring
6 Lag 3

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
10-08

FIGURE 10.8
Completed Gantt Chart for Project
Delta
10-9

FIGURE 10.9
Gantt Chart for Project Delta with
Critical Path Highlighted
10-10

FIGURE 10.10
Gantt Chart with Resources
Specified
10-11

FIGURE 10.11
Gantt Chart with Lag Relationships
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
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
10-14

Project Activities and Costs
10-15
Normal Crashed
Activity Duration Cost Duration Cost
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 $22,450 $37,500
Table 10.1Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall

FIGURE 10.14 Time–Cost Trade-Offs for Crashing Activities
10-16

FIGURE 10.15 Fully Crashed Project Activity Network
10-17

FIGURE 10.16 Relationship Between Cost and Days Saved in a Crashed Project
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
10-19

FIGURE 10.18
Notation for Activity-on-Arrow (AOA)
Networks
10-20

FIGURE 10.19
Sample Network Diagram Using AOA
Approach
10-21

FIGURE 10.20A
Representing Activities with Two or
More Immediate Successors(Wrong)
10-22

FIGURE 10.20B
Alternative Way to Represent
Activities with Two or More
Immediate Successors (Wrong)
10-23

FIGURE 10.20C
Representing Activities with Two or
More Immediate Successors Using
Dummy Activities (Better)
10-24

FIGURE 10.21
Partial Project Delta Network Using
AOA Notation
10-25

FIGURE 10.22
Completed Project Delta AOA
Network
10-26

FIGURE 10.23
Project Delta Forward Pass Using
AOA Network
10-27

FIGURE 10.24
Project Delta Backward Pass Using
AOA Network
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
10-29

Summary
1. Apply lag relationships to project activities.
2. Construct and comprehend Gantt charts.
3. Recognize alternative means to accelerate projects, including
their benefits and drawbacks.
4. Understand the trade-offs required in the decision to crash
project activities.
5. Develop activity networks using Activity-on-Arrow
techniques.
6. Understand the differences in AON and AOA and recognize
the advantages and disadvantages of each technique.
10-30

10-31

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