1. CONSTRUCTION MANAGEMENT AND ADMINISTRATION
UNIT-II

2. Unit II: list of topics Large scale production
Economies of large scale production
Stages of Construction planning and scheduling
Work Breakdown Structure
Bar charts, limitations of bar charts
Network techniques in construction management
CPM and PERT
Network Problems

3. Network techniques in construction management
Network techniques are effective tools for
Planning
Scheduling and
controlling construction jobs
Network techniques provide a rational approach
Application of these techniques essential to meet higher productivities with constraint on resources such as time, capital, skilled man power, equipment e.t.c.,
The two commonly used network techniques are
Critical Path Method (CPM)
Programme Evaluation and Review Technique (PERT)

4. CPM PERT Developed by US Du Pont Corporation & Remington Rand in 1956
Activity oriented
Single time estimate
Deterministic approach
activities are shown as a network of precedence relationships using activity-on-node network construction
CPM is used for repetitive types of projects where the time estimates for various activities are either known or can be determined accurately
CPM places emphasis upon optimising allocation of resources and minimizing overall project cost
Developed by US Navy during while working on Polaris Missile program
Event oriented
Three time estimates
To , Tl, Tp ,
Probabilistic approach
activities are shown as a network of precedence relationships using activity-on-arrow network construction
PERT is used for pioneering type (R&D) projects and where prior data about activity times is not available
PERT lays emphasis on reducing project completion time without cost constraint

5. Program Evaluation & Review Technique
Three time estimates used in PERT are
Optimistic Time Estimate (To): shortest possible time under ideal conditions
Most likely Time Estimate (Tm): time for completing activity under normal conditions
Pessimistic Time Estimate (Tp): Maximum time required to complete activity under extremely adverse conditions in which everything goes wrong
Expected Time Estimate (Te) = (To + 4Tm + Tp )/6
Estimation Trend assumed to follow Beta Distribution curve
To < Tm < Tp
Std.Deviation of activity =(Tp-To)/6
Higher the SD greater the uncertainty
Variance of activity =(SD)2
Variance reflects the spread of a value over a normal distribution

6. Three time estimates and Expected time
S.No
Activity To Tl Tp Te 1
Driving precast piles for a bridge abutment 22 30 50 2
Erecting roof trusses for factory shed 11 14 17 3
Concreting foundation for turbo-generator
5 1/4 6 4
Fabricating sheet metal AC ducts for an auditorium 12 16 5 SD
4.67
1.00
0.50
0.83 V
21.78
1.00
0.25
0.69 32 14 5
15.5

7. Immediate predecessor
Activity
Immediate predecessor
Opt.Time
Most likely Time
Pessimistic Time a - 10 22 b 20 c 4 16 d 2 14 32 e
b,c 8 f g h 12 I
g,h 6 38 j
d,e
Expected Time 20 10 15 14 4 11 18 8
Std.Dev 2 5
Variance 4 25 5 28

8. Terminology used in Network Techniques
Activity (ij): a specific task, operation, job or function which consumes time & resources and has a definite beginning and end
Event: An instantaneous point in time marking the beginning or end of one or more activities. It consumes no time or resources
Network / Flow diagram: the diagrammatic representation of a work plan showing the activities, step by step, leading to the established goal. It depicts the interdependence among the various activities
Duration (tij): Estimated time required to complete an activity
Dummy activity: activity with zero duration and no resource consumption
SUCCESSOR
PRECEEDING
ACTIVITY
EVENT

9. Basic Rules for developing Network
No activity can commence until all preceding activities have been completed
A dummy activity is introduced in the network either to show dependency or to avoid duplicate numbering of activities
Build Wall 1 3 4
Plaster wall
CC Pier 1 3 4
Erect Beams 2
PreCast Beams

10. Basic Rules for developing Network
Event numbers must not be duplicated
3logics considered to place an activity in the network
Preceding activity
Succeeding activity
Simultaneously occurring activity
No activity should lead back to a previous event (no looping)
Only one start and only one finish
No dangling activity

11. Network elements Sequential Activities Diverging Activities
Converging Activities
Parallel Activities
Build Wall 1 3 4
Plaster wall
CC Pier 1 3 2
PreCast Beams
CC Pier 1 3
Erect Beams 2
PreCast Beams C D A B

12. Situations in network diagramB C
A must finish before either B or C can start A B C
both A and B must finish before C can start D C B A
both A and B must finish before either of C or D can start A C B D
Dummy
A must finish before B can start
both A and C must finish before D can start

13. Examples Of The Use Of Dummy Activity
Examples Of The Use Of Dummy Activity
---Dummy
Network concurrent activities 1 2 3 a
WRONG!!! b
Dummy
RIGHT  1 2
Activity c not required for e a b c d e
WRONG!!!
RIGHT 

14. b and c precede f (a does not precede f)
a precedes d.
a and b precede e,
b and c precede f (a does not precede f)
WRONG!!!
RIGHT!!! a d a d 1 1 b e b 2 2 4 e c f c f 3 3

15. Network Representation
Activity On Node (AON)
Activities are represented on nodes and arrows are used to show the dependency relationships
Duration is also indicated in the node
Activity On Arrow (AOA):
Activities are represented by Arrows drawn left to right
Activity description written above the arrow and duration below it
An event is graphically represented by a number enclosed in a circle
The beginning of an activity is marked by a “tail event” or preceding event and the end by a “head event” or succeeding event A 2
start B 3
Pour concrete
Tail Event 1 2
Head Event
2 Days

17. Immediate Predecessor
Network Development
Events 1 2 3 4 5 6 7 8 9 10
Immediate Predecessor -
3,5
3,4
3,7
3,6,8,9 4 7 9 8 1 2 3 10 6 5

18. Network Development 7 4 2 10 5 9 1 6 3 8 X K E Q Z A B J C F G
Activities: A,B,E,Q,K,X,J,Z,G,F,C
Logic
A&B can be carried out at the same time. They represent the beginning of the job
K follows E
X depends on Q&K
Neither F nor G can be started before B is completed, but they can be concurrently performed
E&Q follow A
Q must be carried out before J
C depends on the completion of F&G
E&Q can be executed at the same time
Z can only be started when C,X and J are finished
Z is the last activity 5 X 7 4 K 2 E Q 9 Z 10 1 A B J 6 C 8 3 F G

19. Network Development 2 4 1 3 6 5 S N O M R P Q T
Activities: M,N,O,P,Q,R,S and T
Logic
Activities M,N and Q can start concurrently and represent start of the project
Activities O&P are concurrent and depend on completion of both M&N
Activities R&S are concurrent and depend on the completion of O
Activity T depends upon the completion of P,Q&R
The project is complete when S&T are completed 2 4 1 M Q N S O 3 6 R T P 5

20. Immediate predecessor
Network Development ..
Activity
Immediate predecessor a - b c d e
b,c f g h I
g,h j
d,e d 2 5 1 b c a j e f 7 3 g i 4 6 h

21. Network Analysis
Earliest Event Time(TE): It is the earliest possible occurrence of an event i.e. the earliest possible time when all activities leading to an event will be completed.
Early Start Time (EST)
Early Finish Time (EFT)
Latest allowable Event Time (TL): ): It is the latest possible occurrence of an event without delaying the project completion time i.e. the latest time when all activities leading to an event may be completed without delaying project completion time
Late Start Time (LST)
Late Finish Time (LFT)

22. Float in Activities
Total Float (FT): The maximum time by which an activity can be delayed without delaying project completion time.
FT =LST-EST=LFT-EFT
Free Float= TEj-EFT
Independent Float=(TEj – TLj)- tij
Critical Activities: Activities which have zero total float
Critical Path: The path joining the critical activities

23. Network Analysis Forward Pass: Backward Pass:
Determine EST and EFT for each Task
For all Initial Tasks, EST = 0, EFT equals EST plus Duration
The EST for all other tasks with tail [i] is equal to the largest value of EFT for all tasks with head [i]
Project Completion Time is the largest value of EFT for all Final Tasks
Backward Pass:
Determine LFT and LST for each Task
For all final Tasks, LFT =EFT, LST equals LFT minus Duration
The LFT for all other tasks with head [j], is equal to the smallest value of LST for all tasks with tail [j]
At least one Initial Task must have LST = 0; none may be negative

24. Activity (ij)
Duration (Tij)
Earliest
Latest
Total Float
EST
EFT
LST
LFT
1-2 2
1-3 3
2-4 4
3-4 5
4-5 6
Draw Network
Calculate float
Identify Critical Path 2 2 4 2 3 3 2 6 4 8 2 3 8 3 8 8 14 8 14
Critical Path: 4 5 1 2 2 4 6 3 5 3

25. Critical Path: a-b-c-d-e-f
Activity (ij)
Duration (Tij)
Earliest
Latest
Total Float
EST
EFT
LST
LFT
a-b 6
a-c 8
b-c 4
c-d
b-d 3
c-e
d-e 10
e-f
Draw Network
Calculate float
Identify Critical Path 6 6 8 2 10 2 6 10 6 10 10 10 10 10 6 9 7 10 1 10 16 14 20 4 10 20 10 20 20 23 20 23
Critical Path: a-b-c-d-e-f d a b 6 3 4 10 8 c e f 3 6

26. Activity (ij)
Duration (Tij)
Earliest
Latest
Total Float
EST
EFT
LST
LFT
1-2 5
1-3 4
2-3
2-4
2-6
7.5
3-4
5.5
3-5
6.2
4-5
6.3
4-6
5-6
4.3
Draw Network
Calculate float
Identify Critical Path 5 5 4 1 5 1 5 5 5 5 5 9
6.5
10.5
1.5 5
12.5
13.6
21.1
8.6 5
10.5 5
10.5 5
11.2
10.6
16.8
5.6
10.5
16.8
10.5
16.8
10.5
15.5
5.6
16.1
21.1
16.8
21.1
16.8
21.1 2 6
7.5 4 5 5 4
4.3
5.5 1
6.3 4
6.2 5
Critical Path: 3

27. BENEFITS of CPM/PERT Network in execution of projects
Consistent framework for planning, scheduling, monitoring, and controlling project
Calendar-wise construction schedule of activities useful to draw schedule of men, machinery and material
Inter-relationship and sequence of various activities are clear from network
During execution of the work the productivity constants can be revised
In the event of the program getting upset due to some unforeseen reasons, a revised CPM chart can be prepared and prompt action can be taken to avoid further loss of resources
The network scheduling ensures the optimum use of the men, machines and material
The executive gets a reliable and valuable aid to assess progress of the work

28. BENEFITS OF CPM / PERT NETWORK (cont.)
Helps proper communication between departments and functions.
Determines Expected project completion date
Identifies critical activities, which can delay the project completion time
Identifies Non-critical activities with slacks that can be delayed for specified periods without penalty, or from which resources may be temporarily borrowed
Determines the dates on which tasks may be started or must be started if the project is to stay in schedule.
Shows which tasks must be coordinated to avoid resource or timing conflicts.
Shows which task may run in parallel to meet project completion date

29. Clarifications and discussion…..

30. Determine the critical path in the network shown below and calculate earliest project completion time . Assume that the project starts at zero time. 10 10 2 D A C 12 10 9 33 33 19 19 47 47 10 12 G I K 4 5 7 8 1 7 10 14 B E H J 6 8 4 6 F 3 6 6 4 6 27 27

31. Determine the critical path in the network shown below and calculate earliest project completion time . Assume that the project starts at zero time. 4 5 1 D 5 10 10 A 3 11 11 6 K J 7 L 1 8 8 2 5 4 4 E 16 16 4 I B 2 8 1 4 4 H F 3 4 C 5 2 G 8 8 6 3 7 10

32. 5 d h g a e b 1 2 3 4 7 8 c f 6 2. Await quotations for the new mixer
1. Prepare specifications and call quotations
6.Install power supply
7. Install new mixer
8. Connect power supply
5. Prepare platform for installation of mixer
3. Prepare comparative statement and place order
4. Await delivery of mixer 5 d h g a e b 1 2 3 4 7 8 c f 6