© 2007 Pearson Education

The logical relationship between the start and finish of one activity and the start and finish of another activity.

Four logical relationships between tasks1. Finish to Start2. Finish to Finish3. Start to Start4. Start to Finish

Most common type of sequencing Shown on the line joining the modes

› Added during forward pass› Subtracted during backward pass

0 A 6Spec Design

6

6 B 11Design Check

5

15 C 22Blueprinting

7

Lag 4

This lag is not

the same as

activity slack

Two activities share a similar completion point› The mechanical inspection cannot happen

until wiring, plumbing, and HVAC installation are complete

10 A 16Plumbing

6

16 B 21HVAC

5

21 C 22Inspection

1

15 D 21Wiring

6

31 A 33Plumbing

6

33 B 36HVAC

5

36 C 37Inspection

1

30 D 36Wiring

6

Lag 3

Logic must be maintained by both forward and backward pass

Least common type of lag relationship

Successor’s finish dependent on predecessor’s start

22 A 28Plumbing

6

28 B 33HVAC

5

33 C 34Inspection

1

30 D 36Wiring

6Lag 3

Establish a time-phased network Can be used as a tracking tool

Benefits of Gantt charts1. Easy to create and comprehend2. Identify the schedule baseline network3. Allow for updating and control4. Identify resource needs

Create a Gantt chart based on the activities listed in the table.

Exercise:-

Task Time Pred Task Time Pred

Z 8 -- U 3 W

Y 5 Z T 6 V

X 8 Z S 7 U,T

W 4 Y,X R 9 S

V 5 W

Accelerating a project by committing more resources than initially planned

Principal methods for crashing Improving existing resources’

productivity Changing work methods Increasing the quantity of resources

Determine activity fixed and variable

costs

The crash point is the fully expedited

activity

Optimize time-cost tradeoffs

Shorten activities on the critical path

Cease crashing when› the target completion time is reached› the crash cost exceeds the penalty cost

What is the lowest additional cost to complete this project in 53 weeks? Times are in weeks and costs in dollars.Activity Pred Normal

TimeMin

TimeNormal

CostCrash Cost

A -- 14 9 500 1500

B A 5 2 1000 1600

C A 10 8 2000 2900

D B, C 8 5 1000 2500

E D 6 5 1600 1900

F D 9 6 1500 3000

G E, F 7 4 600 1800

H G 15 11 1600 3600

Activities represented by arrows Widely used in construction Event nodes easy to flag Forward and backward pass logic similar

to AON Two activities may not begin and end at

common nodes Dummy activities may be required

1. Use AOA to sketch the network that represents the project as described in the table.

2. Calculate early and late start and finish times for all activities.

Activity Time Pred Activity Time Pred

A 4 -- F 4 D

B 2 A G 15 C

C 10 A H 7 E,F,G

D 3 B,C K 11 G

E 15 B

Networks can be too complex

Poor network construction creates

problems

Networks may be used inappropriately

When employing subcontractors› The master network must be available to them› All sub-networks must use common methods

Positive bias exists in PERT networks