Executing the Project

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Chapter10.ProjectSchedulingLaggingCrashingandActivityNetworks1.pptx

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Project Management: Achieving Competitive Advantage

Fifth Edition

Chapter 10

Project Scheduling: Lagging, Crashing, and Activity Networks

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Learning Objectives

10.1 Apply lag relationships to project activities.

10.2 Construct and comprehend Gantt charts.

10.3 Recognize alternative means to accelerate projects, including their benefits and drawbacks.

10.4 Develop activity networks using Activity-on-Arrow techniques.

10.5 Understand some of the important controversies in the use of project networks.

P M B o K Core Concepts (1 of 2)

Project Management Body of Knowledge (P M B o K) covered in this chapter includes:

Plan Schedule Management (P M B o K 6.1)

Define Activities (P M B o K 6.2)

Sequence Activities (P M B o K 6.3)

Precedence Diagramming Method (P M B o K 6.3.2.1)

Leads and Lags (P M B o K 6.3.2.3)

P M B o K Core Concepts (2 of 2)

Estimate Activity Resources (P M B o K 6.4)

Estimate Activity Durations (P M B o K 6.5)

Develop Schedule (P M B o K 6.6)

Schedule Compression (P M B o K 6.6.2.7)

Control Schedule (P M B o K 6.7)

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:

Finish to Start

Finish to Finish

Start to Start

Start to Finish

Finish to Start Lag

Most common type of sequencing

Shown on the line joining the modes

Added during forward pass

Subtracted during backward pass

Figure 10.2 Network Incorporating Finish to Start Lag of 4 Days

This lag is not the same as activity slack.

Finish to Finish

Two activities share a similar completion point (wiring and H V A C).

The under construction cannot happen until wiring, plumbing, and H V A C installation are complete.

Figure 10.3 Finish to Finish Network Relationship

Finish to Finish Lag

It may be appropriate for two or more activities to conclude at the same time. For example, a contractor building an office complex cannot begin interior wall construction until all wiring, plumbing, and H V A C have been installed; she may include lag to ensure the completion of all preceding activities all occur at the same time.

Figure 10.4 Finish to Finish Relationship with Lag Incorporated

Start to Start Lag

Figure 10.5 Start to Start Network Relationship

Logic must be maintained by both forward and backward pass.

Start to Finish Lag

Figure 10.6 Start to Finish Network Relationship

Least common type of lag relationship

Successor’s finish dependent on predecessor’s start

Gantt Charts

Establish a time-phased network

Can be used as a tracking tool

Benefits of Gantt charts

Easy to comprehend

Identify the schedule baseline network

Allow for updating and control

Identify resource needs

Easy to create

Figure 10.8 Completed Gantt Chart for Project Delta

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

Primary 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

Crash Process

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

Figure 10.14 Time/Cost Trade-Offs for Crashing Activities

Table 10.1 Project Activities and Costs

Activity	Predecessors	Normal Duration	Normal Cost	Crashed Duration	Crashed Cost
A	–	5 days	$ 1,000	3 days	$ 1,500
B	A	7 days	700	6 days	1,000
C	A	3 days	2,500	2 days	4,000
D	A	5 days	1,500	5 days	1,500
E	C, D	9 days	3,500	6 days	9,000
F	B	4 days	1,600	3 days	2,500
G	D	6 days	2,400	4 days	3,000
H	E, F, G	8 days	9,000	5 days	15,000
Total costs =	blank	blank	$22,450	blank	$37,500

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 A O N

Two activities may not begin and end at common nodes

Dummy activities may be required

Figure 10.18 Notation for Activity-On-Arrow (A O A) Networks

Figure 10.19 Sample Network Diagram Using A O A 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 A O A Notation

Figure 10.22 Completed Project Delta A O A Network

Figure 10.23 Project Delta Forward Pass Using A O A Network

Figure 10.24 Project Delta Backward Pass Using A O A Network

Controversies in the Use of Networks

Networks can be too complex.

Poor network construction creates problems.

Networks may be used inappropriately.

Networks pose special dangers because contractors may create their own networks.

Positive bias exists in P E R T networks.

Summary

Apply lag relationships to project activities.

Construct and comprehend Gantt charts.

Recognize alternative means to accelerate projects, including their benefits and drawbacks.

Develop activity networks using Activity-on-Arrow techniques.

Understand some of the important controversies in the use of project networks.