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

PDM

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 StartEF = Earliest FinishLS = Latest StartLF = Latest FinishTF = Total FloatFF = Free Float

Network analysisForward 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

Network analysisBackward 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

Activity

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

Development of a network

Level 1

Level 2

Level 3

Final

Activity FloatCritical 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