project management ch10
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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
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
FIGURE 10.9
Gantt Chart for Project Delta with Critical Path Highlighted
10-10 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
FIGURE 10.10
Gantt Chart with Resources Specified
10-11 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
FIGURE 10.11
Gantt Chart with Lag Relationships
10-12 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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 10.1 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
FIGURE 10.14 Time–Cost Trade-Offs for Crashing Activities
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall 10-16
FIGURE 10.15 Fully Crashed Project Activity Network
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall 10-17
FIGURE 10.16 Relationship Between Cost and Days Saved in a Crashed Project
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall 10-18
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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 10-19
FIGURE 10.18
Notation for Activity-on-Arrow (AOA) Networks
10-20 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
FIGURE 10.19
Sample Network Diagram Using AOA Approach
10-21 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
FIGURE 10.20A
Representing Activities with Two or More Immediate Successors(Wrong)
10-22 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
FIGURE 10.20B
Alternative Way to Represent Activities with Two or More
Immediate Successors (Wrong)
10-23 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
FIGURE 10.20C
Representing Activities with Two or More Immediate Successors Using
Dummy Activities (Better)
10-24 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
FIGURE 10.21
Partial Project Delta Network Using AOA Notation
10-25 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
FIGURE 10.22
Completed Project Delta AOA Network
10-26 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
FIGURE 10.23
Project Delta Forward Pass Using AOA Network
10-27 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
FIGURE 10.24
Project Delta Backward Pass Using AOA Network
10-28 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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
Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall
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