4E1 Lecture 3 2015

4E1 Project Management Lecture 3

Project Management - Lecture 3

Leo Harmon

4E1 Management for Engineers

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Objective of Lecture From WBS to Network

Differences between them Network to Gantt Worked examples from Gray Larson Concept of Critical Path Concepts of Float/Slack and lag Additional learning material

Chapter 6 Gray & Larson

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WBS to Network WBS

Independently specified - task, resources, costs No analysis of sequence

Network Sequence of tasks Interdependency & scheduling

Maximise the overlap in the people that do WBS and Network Planning Common understanding of WBS terminology

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Network Rules Flow is Left to Right An activity cannot begin until the preceding tasks

are completed Arrows indicate precedence and flow (can cross

over each other) Each activity should have a unique ID Looping is NOT ALLOWED Conditional statements are NOT ALLOWED Project should have a common start and end

node4

4E1 Project Management Lecture 3 5


In Class Exercise 1 From the Following WBS draw network

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Solution to Task 1

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Project NetworksProject networks have some specific characteristics:

Arrows/links represent a task or activity

and its duration - hence “Activity on Arrow” (AOA)

conventionally run left-right One and only one

starting node completion node link between each pair of

nodes (why?)

• At least one path from start to completion

• No circuits or loops• May be

• multiple paths from start to completion

• special activities, and thus links, with zero duration

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Project Network Features Critical path

If all tasks on a path from start to completion have zero slack, the path is on the critical path

Time delay risk of the project! Sub-critical activities

Activities with a small free float are sub-critical activities

Slack Typical task has earliest start

and latest completion times Slack = LC - ES

Free float Activities that can start late or

finish early have free float

Interfering float An activity that can only be

delayed in its float at the expense of some other activity’s float has an interfering float

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Why Critical Path? Minimise

Total project time

Total project cost

Cost for a given time

Time for a given cost

Idle resources

CPA methods used as:

planning tools

control tools

Many software packages can calculate the path

May be > 1 critical path

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Critical Path Method (CPM)

To find the critical path three steps are required Requires care and thought Easy to make a mistake

1.Forward pass

Traverse network from start, calculating earliest possible completion time of each task.

This will give you a total time for the project.

2.Backward pass

Working backwards from end, calculate latest completion time needed to complete each activity’s preceding task.

3.Identify critical path

Nodes where the forward earliest completion time equals the backward latest completion lie on the critical path.

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Forward Pass How soon can an activity

start? Earliest Start (ES)

How soon can an activity Finish? Earliest finish (EF)

Goal: Project Completion Time

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ES ID EF

Description

Duration

4E1 Project Management Lecture 3 13

ES A EF

Description

Duration

Task A: Project Kick off 1Task B: Dig Foundations 5Task C: Order concrete 1Task D: Pour Concrete 1

ES B EF

Description

Duration

ES C EF

Description

Duration

ES D EF

Description

Duration


Durations

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0 A 1

Kickoff

1


1 B 6

Dig foundations

5

1 C 2

Order Concrete

1

6 D 7

Pour Concrete

1

ES A EF

Description

Duration


Exercise 2 Complete Forward Pass

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Solution to Forward Pass

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Backward Pass How Late can an activity

start? Latest Start (LS)

How Late can an activity Finish? Latest finish (LF)

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ES ID EF

Description

LS Duration LF


Backward Pass

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0 A 1

Kickoff

0 1 1


1 B 6

Dig foundations

1 5 6

1 C 2

Order Concrete

5 1 6

6 D 7

Pour Concrete

6 1 7

ES A EF

SL Description

LS Duration LF


Exercise 3 Complete Backward Pass

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Solution to Backward Pass

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Slack/Float and the Critical Path How Long can an activity

be delayed? Slack or Float (SL) LS-ES=SL or LF-EF=SL

Critical Path are those tasks with zero Slack

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ES ID EF

SL Description

LS Duration LF


Slack

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0 A 1

0 Kickoff

0 1 1


1 B 6

0 Dig foundations

1 5 6

1 C 2

4 Order Concrete

5 1 6

6 D 7

0 Pour Concrete

6 1 7

ES A EF

SL Description

LS Duration LF


Calculate Slack and Identify CP on Koll case

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Solution to Koll

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Complications

Complications can arise when computing the critical path: Different precedence

relations Multiple projects Resource constraints

Resource sharing Availability constraints

Politics

Tradeoffs•Overtime•Additional resources•Extension of duration•Cost

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Critical Path Put best people on CP Put most effort into Risk Assessment on CP When short of time - focus on the CP and

Practice MBWA Know where you can lend resources safely Know where extra effort will pay big dividends

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Different Precedence Relations

Four important types:

Finish to start Start to start

Finish to finish Start to finish

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Lag Delay between the end of task and start of the

next Transport Approvals and signoff Etc.

Add to the ES or subtract from EF of successor task depending on the precedence relation

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Example using Lag

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Critical Path Probably the most important tool in project

management Sensitivity Analysis Multiple Critical Paths

… then assign resources

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Documents

4E1 Lecture 3 2015