Keanu

Lecture 9

Project Scheduling

Lecturer: Dr. Khalegh Barati

Term 3, 2020

CVEN3101

ENGINEERING OPERATIONS AND CONTROL

Project Scheduling

Project scheduling is determination of the timing of the activities comprising

the project to enable project managers to execute the project in a timely

manner.

Project scheduling provides the listing of activities, deliverables, and

milestones within a project.

A project schedule usually includes the planned start and finish dates, and

the time assigned to each activity.

Effective project scheduling is a critical component of successful project

management.

2

Objectives of Project Scheduling

• Completing the project as early as possible by determining the earliest start

and finish of each activity

• Investigating the effect of possible delays of activities on project completion

time

• Determining critical activities in a project

• Tracking the progress of a project based on the network schedule and

taking corrective actions when necessary

• Smoothing out resource allocation over the duration of a project

• Finding the minimum extra cost required to complete the project by a certain

date by conducting cost-time trade off

• Evaluating the actual performance of a project against its scheduled

performance

3

Project Schedule Management Processes

PMBOK defines the following seven processes for project schedule (time)

management.

Plan Schedule Management

Plan schedule management is the process of establishing the policies,

procedures, and documentation for planning, developing, managing, executing,

and controlling the project schedule. The key benefit of this process is that it

provides guidance and direction on how the project schedule will be managed

throughout the project.

Define Activities

Define activities is the process of identifying and documenting the specific

actions to be performed to produce the project deliverables. The key benefit of

this process is to break down work packages into activities that provide a basis

for estimating, scheduling, executing, monitoring, and controlling the project

work.

4

Project Schedule Management Processes

Sequence Activities

Sequence Activities is the process of identifying and documenting relationships

among the project activities. The key benefit of this process is that it defines the

logical sequence of work to obtain the greatest efficiency given all project

constraints.

Estimate Activity Resources

Estimate activity resources is the process of estimating the type and quantities of

material, human resources, equipment, or supplies required to perform each

activity. The key benefit of this process is that it identifies the type, quantity, and

characteristics of resources required to complete the activity which allows more

accurate cost and duration estimates.

Estimate Activity Durations

Estimate activity durations is the process of estimating the number of work periods

needed to complete individual activities with estimated resources. The key benefit

of this process is that it provides the amount of time each activity will take to

complete, which is a major input into the develop schedule process.

5

Project Schedule Management Processes

Develop Schedule

Develop schedule is the process of analyzing activity sequences, durations,

resource requirements, and schedule constraints to create the project schedule

model. The key benefit of this process is that by entering schedule activities,

durations, resources, resource availabilities, and logical relationships into the

scheduling tool, it generates a schedule model with planned dates for

completing project activities.

Control Schedule

Control schedule is the process of monitoring the status of project activities to

update project progress and manage changes to the schedule baseline to

achieve the plan. The key benefit of this process is that it provides the means to

recognize deviation from the plan and take corrective and preventive actions

and thus minimize risk.

6

Network

• Network is a graphical representation of all the activities and work paths for a

project. Network looks like a chart with a series of boxes and arrows.

• Network clearly shows dependency relationships and determines activities that

must precede (precedent) or follow (succeeding) other activities.

• Network is a powerful tool for scheduling and controlling a project and its

activities.

• There are two types of activity-on-arrow (AOA) and activity-on-node (AON)

networks.

AOA AON

7

Network

Advantages

• Showing precedencies clearly

• Allowing visualization of activities’ relationships and dependencies

• Determining critical path and activities

• Clarifying the impact of changes on subsequent activities and the project

• Being easily adjustable if delays happen in some activities of the project

Disadvantages

• Focusing just on time and assuming that other resources (money, equipment,

HR) are unlimited

• Doesn’t readily depicting durations, dates, and progress

• Would be difficult to develop and use network for large projects

8

Dependency Relationships

Finish-to-Start (FS) B cannot start till A finishes e.g. A: Constructing wall; B: Painting wall

Start-to-Start (SS) B cannot start till A starts e.g. A: Pouring concrete; B: Levelling concrete

Finish-to-Finish (FF) B cannot finish till A finishes e.g. A: Electrical work; B: Plasterboard

Start-to-Finish (SF) B cannot finish till A starts (rare) e.g. A: Evening security shift; B: Morning security shift

9

Lead and Lag Times

• Lead time is the amount of time whereby a successor activity can be

advanced with respect to a predecessor activity. Actually, lead time is the

overlap between the first and second activities.

• Lag time is the amount of time whereby a successor activity is required to be

delayed with respect to a predecessor activity. Actually, lag time is the delay

between the first and second activities.

Activity A

Activity B Activity B

Activity A

Activity B

Activity A

FS with lead FS with lagFS

10

Activity-on-Arrow (AOA) Network

In this method, arrows are used to represent activities, and nodes represent

event such as starting and ending points of activities and project.

The tail of the arrow represents the start of the activity and the head represents

the finish.

2

4

51

3 6

7

A

C F

E B

D

H

G

11

Dummy Activity

Dummy activity is used to identify precedence relationships correctly and to

eliminate possible confusion of two or more activities having the same starting

and ending nodes.

Dummy activities have no resources (time, labour, machinery, etc), and their

purpose is to preserve logic of the network.

Dummy activities can be only used for AOA networks.

Dummy activity is used when:

• There is a situation that there are two parallel activities with the same starting and ending nodes.

• There is a situation that precedencies can not be correctly indicated in the network.

12

Dummy Activity

When do we need to use dummy activity?

1 2 1

2

3

1

2

1

A

EC

D B

A

B

A

B

B

A

E

D

C

d

d

1) Concurrent

activities

2) When activity C

is not the precedent

of activity D.

1

1

4

3

2 B

A D

C

A

E

F

D

B

C

E

F

3) A precedes D. A

and B precede E.

B and C precede F.

A does not

precede F.

d

d d

13

Example

Draw AOA network for a project with the following activities.

Activity A B C D E F G H I J

Predecessor - A B A A B, D, E C, F G G H, I

1

4

2 5 6

8

7 9 10

3

A

B

D

E

C

F G H

D1

J

I D2 D3

Solution:

14

Activity-on-Node (AON) Network

In this network, nodes are used to represent activities, while arrows represent

the precedence and dependency relationships.

A

C F

H

B E

GD

I

15

Example

16

Draw AON network for a project with the following activities.

Activity A B C D E F G H I J

Predecessor - - - A C A B, D, E F G G

Solution:

A

BSTART

C

FINISHI

H

J

F

E

G

D

Videos

https://www.youtube.com/watch?v=gEBMPP0SOnU

https://www.youtube.com/watch?v=wVVuHgcr3Mk

AOA Network

https://www.youtube.com/watch?v=s9XPSVj9KVM

Networks Introduction

https://www.youtube.com/watch?v=YXg0jI3Nbww

https://www.youtube.com/watch?v=pcfDYDZYoDA

Project Schedule Management

17

https://www.youtube.com/watch?v=Wt2W4jzj8is

Dummy Activity

Network Analysis

Identification of the critical path and calculation of project duration involve

determining the following four times for each activity:

✓ Early Start (ES)

✓ Early Finish (EF)

✓ Late Start (LS)

✓ Late Finish (LF)

18

Network Analysis

Early Start (ES)

The earliest time that an activity can start after completion of the preceding

activities. It is calculated by taking the project start date as zero and adding each

activity’s duration following the precedencies up to the activity.

Early Finish (EF)

The earliest time that an activity can be completed if it is started at its early start

time and is completed using its estimated duration. It is calculated by adding the

activity’s duration to its early start time.

Late Start (LS)

The latest time that an activity can be started without delaying the project. It is

calculated by subtracting the activity’s duration from the late finish.

Late Finish (LF)

The latest time an activity can be completed without delaying the scheduled

project completion time. It is calculated by working backward through the logic,

starting at the schedule’s end date and subtracting in turn each activity’s duration.

19

Network Analysis

ES(START) always = 0, EF(START) always = 0

ES(A) = max(EF of all precedent activities)

EF(A) = ES(A) + DUR(A)

ES(FINISH) = LS(FINISH) = EF(FINISH) = LF(FINISH) = Project duration

LF(A) = min(LS of all succeeding activities)

LS(A) = LF(A) - DUR(A)

LS(START) always = 0, LF(START) always = 0

20

Forward Pass

Forward pass analysis is conducted to determine ES and EF times of activities.

An activity can start as soon as the last of its precedent activities is finished.

➢ Evaluate the activity which has no immediate predecessors.

• The earliest start for such an activity is zero ES = 0.

• The earliest finish for such activity is EF = Activity duration.

➢ Evaluate the ES of the activities that the EF of all their immediate precedent

activities have been determined.

• ES = Max EF of all its immediate precedent activities.

• EF = ES + Activity duration.

➢ Repeat this process until all activities have been evaluated.

• EF of the FINISH activity is the earliest finish time of the project.

➢ If there is a START activity in the network, it must be noted that:

• ES(START) always = 0, EF(START) always = 0.

21

Example

Conducting forward pass analysis, calculate the ES and EF of all activities of

the following project.

22

ES EF

name(duration)

LS LF

Solution:

In network analysis, each activity is shown as box below.

Activity A B C D E F G H I J

Predecessor - - A B B E(SS) D, E(5) F C G

Duration 3 5 5 4 6 2 4 5 2 3

Example

0 0 START(0) LS LF

3 8 C(5)

LS LF

20 23 J(3)

LS LF

5 9 D(4)

LS LF

5 7 F(2)

LS LF

5 11 E(6)

LS LF

16 20 G(4)

LS LF

0 3 A(3)

LS LF

0 5 B(5)

LS LF

23 23 FINISH(0) LS LF

7 12 H(5)

LS LF

8 10 I(2)

LS LF

5

23

We start forward pass analysis from START to FINISH.

Backward Pass

Backward pass analysis is to determine the LF and LS times for each activity. An

activity can finish at the earliest start time of its succeeding activities.

➢ Evaluate all activities that immediately precede the finish activity.

• The latest finish for such activities is LF = project completion time.

• The latest start for such activities is LS = LF - activity duration.

➢ Evaluate the LF of the activities that LS of all their immediate succeeding

activities have been determined.

• LF = Min LS of all its immediate succeeding activities.

• LS = LF - Activity duration.

➢ Repeat this process backward until all activities have been evaluated.

➢ For START and FINISH activities:

• LF(FINISH) = LS(FINISH) = ES(FINISH) = EF(FINISH) = project duration

• LS(START) always = 0, LF(START) always = 0

24

Example

Conducting backward pass analysis, calculate the LS and LF of all activities in

the previous example.

25

0 0 START(0) 0 0

3 8 C(5)

16 21

20 23 J(3)

20 23

5 9 D(4)

12 16

5 7 F(2)

16 18

5 11 E(6)

5 11

16 20 G(4)

16 20

0 3 A(3)

13 16

0 5 B(5) 0 5

23 23 FINISH(0) 23 23

7 12 H(5)

18 23

8 10 I(2)

21 23

5

Solution:

We start backward pass analysis from FINISH to START.

Critical Path

• The critical path can be defined as the set or sequence of activities which will

take the longest time to complete.

• The duration of the critical path is the sum of the activities’ times along the path.

• The duration of the critical path represents the minimum time required to

complete a project.

• Critical activities (activities on the critical path) need significant attention.

• The ES and LS of a critical activity are the same. Also, the EF and LF of a

critical activity are the same.

• It is possible to have more than one critical path in a network.

• A delay of a certain amount in a critical activity causes the entire project to be

delayed by the same amount.

26

Example

For the network depicted in the previous example,

A) Determine the critical path and critical activities.

B) Determine project duration.

C) How many days can activity D and F be increased to become a critical

activity?

27

Example

Solution:

28

0 0 START(0) 0 0

3 8 C(5)

16 21

20 23 J(3)

20 23

5 9 D(4)

12 16

5 7 F(2)

16 18

5 11 E(6)

5 11

16 20 G(4)

16 20

0 3 A(3)

13 16

0 5 B(5) 0 5

23 23 FINISH(0) 23 23

7 12 H(5)

18 23

8 10 I(2)

21 23

5

Activities B, E, G, and J are critical, and B-E-G-J is the critical path.

Project duration is 23 days.

Activity D must be increased by at least 7 days to become a critical activity.

Activity F must be increased by at least 11 days to become a critical activity.

Dangling Activity

Dangling activities (also known as dangles) are loosely-tied activities in project

schedules. They are activities with either open start dates or open end dates.

All activities, except the START activity of a network, need to have a precedent

activity; otherwise, they will have open start date.

All activities, except the FINISH activity of a network, need to have a succeeding

activity; otherwise, they will have open end date.

A project network that contains dangling activities has deficiencies because its

logic is incomplete. This flaw makes the schedule unreliable and inaccurate

because the schedule has not been fully developed, and some activity

dependencies (i.e. logical ties) have not been properly identified.

29

Dangling Activity

Dangling Start Activity

It is an activity with open start which is not dominated by the precedency

relationships. In other words, it is not linked with (FS) or (SS) relationships with

any precedent activity.

Dangling Finish Activity

It is an activity with open end which is not dominated by the succeeding

relationships. In other words, it is not linked with (FS) or (FF) relationships any

succeeding activity.

30

Activity B

Activity A

Activity C

Activity BActivity A

Activity C

FF

SS

FS

FS

Dangling Activity

Problem Start and finish dates of a project cannot be clearly identified in a network with

dangling activities.

Progress monitoring and delays controlling would be difficult in projects with

dangling activities.

Every project activity except the START and FINISH ones must have at least

one precedent and one succeeding activity.

Any project schedule must start with only one starting activity and only one

finishing activity to ensure that proper logical ties can be built into the network.

Solution Dangling start activities must be tied with START activity.

Dangling finish activities must be tied with FINISH activity.

31

Float

• Float (slack) is the amount of time that an activity in a project can be delayed

without causing any delay to its succeeding activities or the project

completion date.

• Another way to look at float is as a measure of criticality of an activity. The

more float an activity has, the less critical the activity is.

• There are different types of float can be measured for each activity including

total float and free float.

1 4

3

2

2 days

4 days

1 day

10 days

32

Float

Total float

Total float is the amount of time which an activity can be delayed without

delaying the project completion date. Knowing total float of an activity, a project

manager knows that the time can be used without changing the status of any

non-critical activity to become critical. Activities with zero total float are critical,

and their path shows critical path.

TF = LS – ES or TF = LF - EF

Free Float

Free float is the amount of time which an activity can be delayed without

delaying the early start of its succeeding activity.

FF = smallest ES (of succeeding activities) – EF (of current activity) – (lag/lead)

33

Example

For the network below,

a) Determine dangling activities.

b) Modify the network and calculate project duration.

c) Calculate TF and FF for each activity.

34

START(0)

F(3)

H(7)

G(6)

D(4)

E(7)

A(5)

B(8)

C(3)

I(5)

K(5)

J(2) FINISH(0)

-2

3

1

2

-4

Example

a) G and I are dangling start activity. C is dangling finish activity.

0 0 START(0) 0 0

3 6 F(3)

18 21

15 22 H(7)

15 22

7 13 G(6)

15 21

9 13 D(4)

11 15

8 15 E(7)

8 15

0 5 A(5)

6 11

0 8 B(8)

0 8

2 5 C(3)

20 23

0 5 I(5)

15 20

18 23 K(5)

18 23

13 15 J(2)

21 23

23 23 FINISH(0) 23 23

-2

3

1

2

-4

b) Project duration is 23 days, and B-E-H-K is the critical path.

35

Example

Activity Duration ES LS EF LF TF FF

START 0 0 0 0 0 0 0

A 5 0 6 5 11 6 0

B 8 0 0 8 8 0 0

C 3 2 20 5 23 18 18

D 4 9 11 13 15 2 0

E 7 8 8 15 15 0 0

F 3 3 18 6 21 15 7

G 6 7 15 13 21 8 0

H 7 15 15 22 22 0 0

I 5 0 15 5 20 15 15

J 2 13 21 15 23 8 8

K 5 18 18 23 23 0 0

FINISH 0 23 23 23 23 0 0

c)

TF = LS – ES or TF = LF – EF

FF = smallest ES (of succeeding activities) – EF (of current activity) – (lag/lead)

36

Videos

https://www.youtube.com/watch?v=XLWTPTpud1g

https://www.youtube.com/watch?v=r63YGghDfPA

https://www.youtube.com/watch?v=bChK4u34RD8

Introduction to Floats and Their Applications

https://www.youtube.com/watch?v=4oDLMs11Exs

https://www.youtube.com/watch?v=-TDh-5n90vk

CPM Analysis

37

Summary

Project Scheduling

• Plan Schedule Management

• Define Activities

• Sequence Activities

• Estimate Activity Resources

• Estimate Activity Durations

• Develop Schedule

• Control Schedule

Network

• Dependency Relationships

• Lead and Lag

• Dummy Activity

AOA

AON

38

Network Analysis

• Early Start (ES)

• Late Start (LS)

• Early Finish (EF)

• Late Finish (LF)

Forward Pass Analysis

Backward Pass Analysis

Critical Path

Dangling Activity

Float

• Total Float

• Free Float