Project Management Ch11 Project Scheduling Critical Chain

Chapter 11

Critical Chain Project Scheduling

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

Chapter 11 Learning Objectives

After completing this chapter, students will be able to:

Understand the differences between common cause and special cause variation in organizations.

Recognize the three ways in which project teams inflate the amount of safety for all project tasks.

Understand the four ways in which additional project task safety can be wasted.

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Chapter 11 Learning Objectives

After completing this chapter, students will be able to:

Distinguish between critical path and critical chain project scheduling techniques.

Understand how critical chain methodology resolves project resource conflicts.

Apply critical chain project management to project priorities.

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Theory of Constraints & Critical Chain Project Scheduling

A constraint limits any system’s output.

The Goal – Goldratt

TOC Methodology

1. Identify the constraint

2. Exploit the constraint

3. Subordinate the system

4. Elevate the constraint

5. Repeat the process

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FIGURE 11.2 Five Key Steps in Theory of Constraint Methodology

11-05 Copyright © 2012 Pearson Education, Inc. Publishing as Prentice Hall


Variation Common Cause

Inherent in the system

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Special Cause

Due to a special circumstance

Managers should

• Understand the difference between the two types

• Not adjust the process if variation is common cause

• Not include special cause variation in risk simulation

• Not aggregate discrete project risks


CCPM and the Causes of Project Delay

How safety is added to project activities

1. Individual activities overestimated

2. Project manager safety margin

3. Anticipating expected cuts from management

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time

25%

50%

80% 90%

Gaussian (lognormal)

Distribution


Wasting Extra Safety Margin 1. The Student Syndrome

a. Immediate deadlines

b. Padded estimates

c. High demand

2. Failure to pass along positive variation a. Other tasks

b. Overestimation penalty

c. Perfectionism

3. Multitasking

4. Path Merging 11-08

FIGURE 11.6

Student Syndrome Model


Effects of Multitasking on Activity Durations

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FIGURE 11.7


FIGURE 11.8

Effect of Merging Multiple Activity Paths



Critical Chain Solutions

Central Limit Theorem

Activity durations estimated at 50% level

Buffer reapplied at project level

– Goldratt rule of thumb (50%)

– Newbold formula

Feeder buffers for non-critical paths

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n


CCPM Changes Due dates & milestones eliminated

Realistic estimates – 50% level not 90%

“No blame” culture

Subcontractor deliveries & work scheduled ES

Non critical activities scheduled LS

Factor the effects of resource contention

Critical chain usually not the critical path

Solve resource conflicts with minimal disruption

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Critical Chain Solutions

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Bob

Feeder

Buffer

Feeder

Buffer

Feeder

Buffer

Project

Buffer Bob

Bob


Critical Chain Project Portfolios

Drum – system-wide constraint that sets the beat for the firm’s throughput

–company policy

–one person

–a department/work unit

–a resource

• Capacity constraint buffer – safety margin between projects

• Drum buffer – extra safety before the

constraint

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Applying CCPM to Project Portfolios

1. Identify the drum

2. Exploit the drum

a. Prepare a schedule for each project

b. Determine priority for the drum

c. Create the drum schedule

3. Subordinate the project schedules (next slide)

4. Elevate the capacity of the drum

5. Go back to step 2

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Subordinating Project Schedules

Schedule projects based on drum

Designate critical chain

Insert capacity constraint buffers

Resolve any conflicts

Insert drum buffers so the constraint is not starved

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CCPM Critiques

No milestones used

Not significantly different from PERT

Unproven at the portfolio level

Anecdotal support only

Incomplete solution

Overestimation of activity duration padding

Cultural changes unattainable 11-18


Summary

Understand the differences between common cause and special cause variation in organizations.

Recognize the three ways in which project teams inflate the amount of safety for all project tasks.

Understand the four ways in which additional project task safety can be wasted.

Distinguish between critical path and critical chain project scheduling techniques.

Understand how critical chain methodology resolves project resource conflicts.

Apply critical chain project management to project priorities.

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