1. LECTURE 2

2. NETWORK DIAGRAMS

3. Nodes = Activities Links = Relationships Construction Network
Elements of a Construction Network – The Precedence Diagram Method (PDM)
Activity 1
Nodes =
Activities
Links =
Relationships
Talk about AOA briefly as another type of network representation and mention that we will cover this later. Also mention that there are several types of relationships (list them out) but for now we will only look at F-S.
Activity 2
Activity 1
Construction
Network
Finish-Start i j

4. Types of Activities on a Network
Start
Finish
Dummy
Activities
Milestones
Activity 1
Tasks

5. Draw a Network Wall Wall Footing Footing Joint
One Set of Wall and Footing Forms are Available

6. Construction Method
Wall 2
Wall 1
Footing 2
Footing 1

7. WBS Task Description Duration 1 Footing 1 5 Days 2 Footing 2 3 Wall 14
Wall 2

8. The Network Diagram 2 Footing 2 4 Wall 2 Start 1 Footing 1 Finish 3
Stress that knowledge of construction and construction methodology is very important here.
There are many ways to draw this network – one is you can start with Footing 2 – two is you can add more detail by scheduling the erection of forms and so on.

9. Can we improve on the Gantt Chart and the Network?
Gantt Chart omits relationships
What happens to activity B and C if A is delayed?
PD does not have the time element
On what day should C start? Is it ok if it starts a day later than planned?
Activity A
Activity B
Activity C
Activity B
Activity A
Activity C

10. Critical Path Method tries to bridge these two gaps

11. CRITICAL PATH METHOD - BASICS

12. Historical Origins
Developed by Dupont and Remington Rand in the 1950’s to manage plant maintenance projects
Prof. John W. Fondahl, Stanford University adapted CPM for Construction in 1961

13. Concept 1 : 4 Key Dates Early Start Date (ESD or ES)
Early Finish Date (EFD or EF)
Late Start Date (LSD or LS)
Late Finish Date (LFD or LF)

14. Total Time Available for Activity AES EF LS LF
Activity A
Activity A TA TA
Use the Final Project in this class as the example to describe these dates
Total Time Available for Activity A

15. Early Finish Date ES EF
Activity A TA
EFA = ESA + TA

16. Early Start Date ESJ = Max EFi V i ESA EFA = 10 ESc ? = 10 ESB EFb = 8
Activity A
Activity B
Activity C i j i
ESc ?
= 10
ESB
EFb
= 8
ESJ = Max EFi V i

17. Late Finish Date LFi = Min LSj V j LSB =8 LFB LFA? =6 LSC =6 LFC
Activity B
LFA? =6 j
Activity A i
Activity C j
LSC =6
LFC
LFi = Min LSj V j

18. Late Start Date LS LF
Activity A TA
LSA = LFA - TA

19. Concept 2: 12 Relationships
4 categories of relationships
Finish-Start Relationships (F-S)
Start-Start Relationships (S-S)
Finish-Finish Relationships (F-F)
Start-Finish Relationships (S-F)
Three types for each category
No lag
Positive lag
Negative lag
4 x 3 = 12 relationships
Just as for ragas in Carnatic music – all of these 12 relationships do not make sense and so in practice we will have a smaller subset
Ask for examples for each type here and on each of the following pages

20. Finish-Start Relationships
+ve lag
No lag
1 day
1 day
1 day
Place Forms
Pour Roof Slab
Remove Slab
Shoring 14
3 days
2 days
Place Forms and Pour slab has no lag. Slab and remove shuttering has 14 day lag. Pour foundations can take place a day before the excavation ends because the site is large and foundations can be poured on the already excavated portion.
Excavate
Pour
Foundations -1
-ve lag

21. Start-Start Relationships
1 day
Place
Forms
1 day
No lag
Prepare
Rebar
3 days
Excavate
2 days
+ve lag
1 day
Pour
Foundations
First has no lag. Second and third have positive lag.
FS with lag can be SS with lead, as in the second picture above
Start-Start relationship with negative lag can be replaced by S-S with positive lag by alternating the activities. So this representation is not used much. It is useless and confusing.
There is a difference between F-S and S-S. For instance, as soon backfill is done and a PCC coating is provided, placing forms as well as creating reinforcing ties can start. However, if the forms are not available, then the reinforcement will lie and rust if it is a F-S relationship. On the other hand if it is S-S, then reinforcement starts later and this avoids rusting. SS therefore facilitates Lean and JIT construction
6 months
Design
1 Year
+ve lag
3 months
Construct

22. Finish-Finish Relationships
1 day
Grade
End-Sems
4 months
No lag
Prepare
Final
Grades
1 day
First has no lag
Second has positive lag
FF with negative lag is usually not done as the activities can be rearranged and the lag could become positive.
Grade
End-Sems
1 day
4 months
+ve lag
Prepare
Final
Grades

23. Start-Finish Relationships
1 day
Interior Wood
Paneling
2 days
No lag
Interior
Carpeting
It is probably easier to represent this as a Finish-Start Relationship
S-F relationships are rarely used – except in showing combined relationships.

24. More on Relationships Lags can be represented as percentages
Most Relationships are “Can” relationships
B CAN finish when A finishes
B CANNOT finish before A
B can be delayed and finish after A
Second activity can usually be delayed
2 days A
2 days B

25. Concurrent Activities
Test Mock-up Wall
Build Forms
These two activities are completely concurrent as they have SS and FF relationships. Ask the class for some examples here.
Get Wall Shop
Drawings Approved
Assemble Rebar

26. Representing Activities
Early Start
Activity Number/Free Float
Early Finish
Activity Name and Duration
Late Start
Total Float
Late Finish