9-1

ELC 347 project management

Day 19

Agenda

• Integrative Project – IP part 4 not graded yet– Part 5 Due Nov 22 (page 318) – Any of the first five sections can be resubmitted for rescoring prior to finals

week. The recorded score will the average of the original score and the score on the resubmitted section.

• Assignment 7 posted, Due Nov 18 • Exam 2 Nov 22

– Chap 6-10

• Today will discuss Project Scheduling: Lagging, crashing and Activity networks

6-2

Schedule for rest of semester

• Today

– Chap 10

• Nov 18

– Group work

– Assignment 7 due

• Nov 22

– Quiz 2• Chaps 5-10

– IP part 5 Due

• Nov 29

– Chap 11

• Dec 2

– Chap 12

• Dec 6

– Group Work

– Assignment 8 due

• Dec 9

– Chap 13 & 14

– IP Part 6 due

• Dec 13 @ 1 PM

– Quiz 3• Chaps 11 - 15

– IP Project’s due

6-3 © 2007 Prentice-Hall, Inc

Project Scheduling: Lagging, Crashing and Activity

NetworksChapter 10

© 2007 Pearson Education

Lags in Precedence Relationships

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

Four logical relationships between tasks

1. Finish to Start

2. Finish to Finish

3. Start to Start

4. Start to Finish

Finish to Start Lag

• 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

Finish to Finish Lag

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

Start to Start Lag

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

Start to Finish Lag• Least common type of lag relations

hip

• Successor’s finish dependent on predecessor’s start

22 A 28Plumbing

6

28 B 33HVAC

5

33 C 34Inspection

1

30 D 36Wiring

6

Lag 3

fssf.mpp

Gantt Charts

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

Benefits of Gantt charts

1. Easy to create and comprehend

2. Identify the schedule baseline network

3. Allow for updating and control

4. Identify resource needs

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

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

gantt.mpp

Gantt Chart With Resources in MS Project

Crashing Projects

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

CRASHING PROJECTS – UNDER WHAT CONDITIONS?

• The initial schedule may be too optimistic.  • Market needs change and the project is in

demand earlier than anticipated. • The project has slipped considerably behind

schedule. • The contractual situation provides even more

incentive to avoid schedule slippage.

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Managerial Considerations

• 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

Project costs

Pre Normal Crashed Crash/day Days Gained

activity Duration Cost Duration Cost

A 5 1000 3 1500 250 2

B A 7 700 6 1000 300 1

C A 3 2500 2 4000 1500 1

D A 5 1500 5 1500 - 0

E C,D 9 3750 6 9000 1750 3

F B 4 1600 3 2500 900 1

G D 6 2400 4 3000 300 2

H E,F,G 9 900 5 15000 2000 4

Total 22450 37500

Other costs

• Previous examples only includes direct costs• What about

– Indirect costs (overhead)• $ per day overhead

– Late penalties• $ per day late

What is the lowest 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

crash.mpp, crash.xls

Activity on Arrow Networks

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

Project delta

Activity Pre Duration

A 5

B A 5

C A 6

D B,C 13

E B 6

F D 4

G C 9

H E,F,G 2

Two Succesors

AOA Network

Forward Pass

Backwards pass

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 3 -- F 4 D

B 5 A G 2 C

C 7 A H 5 E,F,G

D 3 B,C

E 5 B

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Controversies in the Use of Networks

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