GE 404 (Engineering Management), Slides of Engineering management

Download GE 404 (Engineering Management) and more Slides Engineering management in PDF only on Docsity!

LECTURE # 6

Precedence Diagramming and Time Scaled

Network

ENGINEERING MANAGEMENT

(GE 404 )

بسم هللا الرحمن الرحيم

Objectives of the Present lecture

 To explain how to draw Precedence network

diagrams

 To discuss how to calculate Early/Late

Start/Finish Times in Precedence Network

diagrams.

 To discuss steps involved in drawing the Time-

scaled network diagrams

Activity Relationships

 Finish-to-Start (FS)

 In a finish-to-start relationship, the start of an activity depends on the completion of its

preceding activity.

 Example: Footing excavation must be completed prior to placing concrete for the footing

 Start-to-Start (SS)

 In a start-to-start relationship, an activity can not start before its preceding activity starts

 Example: Project management activities can not start before the Project work starts

 Finish-to-Finish (FF)

 In a finish-to-finish relationship, the two activities are related by the fact that they must be

completed at the same time

 Example: In a simple task of setting a flagpole, the backfilling task and the positioning the

pole task will be finished at the same time.

 Start-to-Finish (SF)

 In start-to-finish relationship, the finish of an activity depends on the start of its preceding

activity (A rare relationship)

 Example: In a Hospital emergency, the previous shift can not finish before the new shift starts

 Say you’re building a new gas pipeline. You would first finish construction and implementation of the new pipeline before you would

begin shutting down and breaking down the old pipeline.

Lag

 The amount of time that exists between the early finish of an

activity and the early start of a specified succeeding activity

 Calculate lags for each link by determining the difference

between the ES of each activity following a link line and the EF

of the activity that precedes it

 Limitations and Disadvantages of Lag:

 Lag would complicate the scheduling process

 Lags are not extensively used except where the time effects

are substantial for special project type

Start-to-Start Activity Precedence Relationships with

Lag Values

j i ij

ES  ES  SS

j j j

EF  ES  D

i j ij

LS  LS  SS

i i i j ij i

LF  LS  D  LS  SS  D

Activity i

Activity j

Activity k

SS

ij

SS

jk

ij ij jk jk

Note:lag  SS and lag  SS

Finish-to-Finish Activity Precedence Relationships

with Lag Values

j i ij j j j

ES  EF  FF  D  EF  D

j i ij

EF  EF  FF

i j ij i i i

LS  LF  FF  D  LF  D

i j ij

LF  LF  FF

Activity i

Activity j

Activity k

FF

ij

FF

jk

ij ij jk jk

Note:lag  FF and lag  FF

Note on SF

ij

 Activity j cannot finish till i

starts (rare)

 SF

ij

is equal to the minimum

number of time units that

must transpire from the start

of the predecessor i to the

completion of the successor

j.

Example

 For the shown diagram

calculate total lag if

SFij

i

j

SFij

ij ij ij

SF SF SF

The finish of j must lag 10

units after the start of i

4 and 6

' ''

ij ij

SF SF

Summary

Finish-to-Start Relationships with Lag Values FS ij

:

j i ij

ES  EF  FS

Start-to-Start Relationships with Lag Values SS ij :

j i ij

ES  ES  SS

Finish-to-Finish Relationships with Lag Values FF ij :

j i ij j

ES  EF  FF  D

Start-to-Finish Relationships with Lag Values SF ij

:

j i ij j

ES  ES S F  D

i j ij

LF  LS  FS

i j ij i

LF  LS  SS  D

i j ij

LF  LF  FF

i j ij i

LF  LF  SF  D

Composite Start-to-Start and Finish-to-Finish (ZZ ij

)Activity

Precedence Relationships with Lag Values

ZZ

ij

is a combination of two constraints, i.e., a start-to-start and

finish-to-finish relationship. It is written with the SS

ij

time units

first, followed by the FF

ij

time units.

Example: ZZ ij

= 5 , 6

The start of activity j must lag 5 units after the start of activity i & The finish of

activity j must lag 6 units after the finish of activity i

Representation

ES Duration EF

Activity (i)

LS Total Float LF

ES Duration EF

Activity (j)

LS Total Float LF

Constraints with lag/lead Durations

ij ( ij ij )

ij

ij

ij

ij

ZZ SS FF

SF

FS

FF

SS



Problem- 1

For the given precedence diagram, complete the forward and backward pass calculations.

Assume the project starts at T= 0 , and no splitting on activities is allowed. Also assume that

the project latest allowable completion time (project duration) is scheduled for 30 working

days.

FS 0

SS 3

FF 4

SS 6

SF 12

FS 0

A

Develop

system spec.

( D= 8 )

C

Collect

system data

( D= 4 )

D

Test & debug

program

( D= 6 )

E

Run

program

( D= 6 )

F

Document

program

( D= 12 )

B

Write comp.

program

( D= 12 )

ES D EF

Activity ID

LS TF LF

Solution

Step- 1 : Network diagram

A

B

D

C

END

E

F

ES D EF

Activity ID

LS TF LF

Activity D

15 6 21

D

D

D

ES

D

EF

BD

FS

B

EF

Initial Time Max(B) D

ES

Activity E

InitialTime 0

E

D

E

ES

E

EF

CE

FS

C

OR EF

DE

FS

D

EF

Max C D E

ES

Activity F

InitialTime 0

( )

F F F

C CF

D DF F F

EF ES D

OR EF FS

ES Max D ES SF D

j j j

i ij j

i ij j

i ij

i ij

j i

EF ES D

ES SF D

EF FF D

ES SS

EF FS

ES Maxall

[ 2 ]

InitialTime

[ 1 ] ( )

Contd.

A

B

D

C

END

E

F

0 8 3 15

9 13

15 21

21 27

15 27

27 27

FS 0

SS 3

FF 4 SS 6

SF 12

FS 0