Project Management Ch10

Chapter 10

Project Scheduling: Lagging, Crashing, and Activity

Networks

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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.

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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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Finish to Start Lag

• Most common type of sequencing

• Shown on the line joining the modes – Added during forward pass

– Subtracted during backward pass

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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

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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

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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

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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 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall

FIGURE 10.9

Gantt Chart for Project Delta with Critical Path Highlighted


FIGURE 10.10

Gantt Chart with Resources Specified


FIGURE 10.11

Gantt Chart with Lag Relationships



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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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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Project Activities and Costs

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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


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



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


FIGURE 10.19

Sample Network Diagram Using AOA Approach


FIGURE 10.20A

Representing Activities with Two or More Immediate Successors(Wrong)


FIGURE 10.20B

Alternative Way to Represent Activities with Two or More

Immediate Successors (Wrong)


FIGURE 10.20C

Representing Activities with Two or More Immediate Successors Using

Dummy Activities (Better)


FIGURE 10.21

Partial Project Delta Network Using AOA Notation


FIGURE 10.22

Completed Project Delta AOA Network


FIGURE 10.23

Project Delta Forward Pass Using AOA Network


FIGURE 10.24

Project Delta Backward Pass Using AOA Network



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

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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

Project Management Ch10

Education

Transcript of Project Management Ch10