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Network planning

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Network planning

Learning objectives

After these lectures you should be able to:

Produce and analyse activities networks

Calculate earliest and latest start and finishing times

for activities

Calculate activity floats and determine the critical

path(s) through a network

- Update networks as new information becomes available

Footings/1 wk Brickwork/3 wks Roof/ 2 wks

Landscape/1 wk Fence/1 wk

A

ES EF

t

LS LF

TF FF

A = Activity description, i.e. ‘Brickwork’

t = Duration (usually in work days)

ES = Earliest Start

EF = Earliest Finish

LS = Latest Start

LF = Latest Finish

TF = Total Float

FF = Free Float

Forward pass

0 1 1 4 4 6 6 8

A/1 B/3 D/2 F/2

1 1.5 1.5 2

C/0.5 D/0.5

ES EF NOTE: ES for the first activity is ‘0’, not ‘1’!

Name/Duration

Backward pass

0 1 1 4 4 6 6 8

A/1 B/3 D/2 F/2

0 1 1 4 4 6 6 8

1 1.5 1.5 2

C/0.5 D/0.5

5 5.5 5.5 6

ES EF NOTE: The backward pass starts with the same

Name/Duration LF value as the last EF for the final activity

LS LF

Draw an PDM network for this project. Then do a forward and backward pass.

Activity Duration Depends on

A 5 None

B 5 A

C 12 A

D 3 C

E 6 B and 2/3 of C

F 8 B and 2/3 of C

G 14 A

H 5 D, E, F and G

Solution 13 21

F/8

13 21

0 5 5 10 13 19

A/5 B/5 E/6

0 5 8 13 15 21

5 13 13 17 17 20 21 26

C1/8 C2/4 D/3 H/5

5 13 14 18 18 21 21 26

5 19

G/14

7 21

Level 1

Level 2

Level 3

Final

Critical activities: Have no float and are therefore fixed in time.

ES = LS and EF = LF

Total Float (TF): The amount of time that an activity can be delayed,

without that affecting the project completion time.

TF = LF – EF = LS – ES

Free Float (FF): The amount of time an activity can be delayed, without

that affecting the start of any following activity.

FF = ES(any following activity) – EF

13 21

F/8

13 21

0 5 5 10 13 19

A/5 B/5 E/6

0 5 8 13 15 21

5 13 13 17 17 20 21 26

C1/8 C2/4 D/3 H/5

5 13 14 18 18 21 21 26

5 19

G/14

7 21

Determine the Critical Paths(s) and all activity floats!

Activity TF FF Critical?

A 0 0 Yes

B 3 3

C1 0 0 Yes

C2 1 0

D 1 1

E 2 2

F 0 0 Yes

G 2 2

H 0 0 Yes

Critical Path = A - C1 - F - H

13 21

F/8

13 21

0 5 5 10 13 19

A/5 B/5 E/6

0 5 8 13 15 21

5 13 13 17 17 20 21 26

C1/8 C2/4 D/3 H/5

5 13 14 18 18 21 21 26

5 19

G/14

7 21

Critical Path (A – C1 – F – H) highlighted in network

Tutorial: Critical Path Method (CPM)

Carry out a critical path analysis for the following project in order to determine the total completion time for the project and the critical activities. Illustrate the critical path(s) in the CPM network. Calculate and list the Total and Free floats for all activities.

Activity Duration Depends on activity

A 3 weeks -

B 2 -

C 5 A

D 6 A and B

E 4 Half of D

F 4 C

G 5 D

H 8 C and E

I 9 D

J 6 I and H

K 18 B

L 4 K