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MODULE 8 NOTES CEM (1).pdf
1. MODULE 8
CONSTRUCTION COSTS
Lesson 1
Fast-Tracking vs. Crashing, Relationship
between Activity Direct Cost & Activity
Duration – Assumptions
(PROF. R K CHOUDHARY
GCE GAYA)
2. Learning Objectives
• Fast-tracking vs Crashing
• Relationship between activity direct cost &
activity duration – Assumptions
• Procedure for finding minimum direct cost for
crashed project durations
• Influence of indirect cost and relationship
between total cost and project duration
3
3. 5 4d 9
B
7 11
5d 5
A
11 3d
D
5 11
5 6d 11
C
5 11
0 14
0 14
Activity Duration Predecessor
A 5 -
B 4 A
C 6 A
D 3 B,C
Consider the ABCD Project
Current duration : 14 days
Expected duration : 10 days
How can it be done ?
4. Reducing Project Duration
• Fast-Tracking
– Preforming activities in parallel in order to reduce project duration
• Crashing
– Reducing duration of activities in order to reduce project duration
Change of execution sequence or duration will have cost implication.
Time-Cost Trade-Off analysis is used to find the minimum
overall project cost for a specified project duration
Focus is on Crashing 5
5. Crash Cost
Cost of completing activity in
minimum duration
Terminology
6
Normal Cost
Cost of completing activity in
normal duration
CRASHING
Reducing activity time by
expending additional resources
Normal Duration
Normal activity duration
Crash Duration
Minimum duration
6. Activity Duration Reduction
• Construction Method Selection
• Alternate Construction Materials
• Working Multiple Shifts
• Overtime work (Late hours or Weekends)
• Bringing in Higher Capacity Equipment
• Additional Workers or Equipment
7
Reducing duration will require additional expenditure
7. Activity: Time vs Cost - Relationship
Crash cost
Linear - Assumption
Piecewise Linear - Assumption
Actual Relationship
Normal
cost
Crash time Normal
time
Activity time
8
Cost Slope = cost / time
= (Crash cost – Normal cost)
(Normal time – Crash time)
9. B
7 11
5d 5
A
5
113d
D
11
5 6d 11
C
5 11
Act ND
days
Pred CD
days
NC
u
CC
u
A 5 - 3 250 300
B 4 A 3 300 375
C 6 A 3 350 875
D 3 B,C 2 300 350
5 4d 9
0 14
0 14
Back to the ABCD Project
Determine Minimum Cost of Completing Project in 13, 12…8 days.2
10. B
7 11
5d 5
A
5
113d
D
11
5 6d 11
C
5 11
CC/day = (CC-NC) /(ND-CD)
Act ND
days
Pred CD
days
NC
u
CC
u
Crash
Days
Crash
Cost /
day
A 5 - 3 250 300 2 25
B 4 A 3 300 375 1 75
C 6 A 3 350 875 3 175
D 3 B,C 2 300 350 1 50
5 4d 9
0 14
0 14
Crashing the ABCD Project
Paths : ABD – Non Critical 12 days
ACD – Critical 14 days
11. B
11
5
4d
A
4
5
11
03d
D
11
0
4
5 6d 11
C
4
5 11
0
Act ND
days
Pred CD
days
NC
u
CC
u
Crash
Days
Crash
Cost /
day
A 5 - 3 250 300 2 25
B 4 A 3 300 375 1 75
C 6 A 3 350 875 1 175
D 3 B,C 2 300 350 1 50
4d 8
9
0
0
14
3
14
Step 1: Crash the critical path
ACD.
Options available to crash
A= u 25
C= u 175
D= u 50
Crash A by 1 day: Cost = u 25
Still the critical path is ACD (13 days)
ABCD Project Crash Duration - 13 days
7
6
12. 4
3 4d 8
7
B
1
90
4
3d
A
A
4
3
10
1
903d
D
D
9
4 6d 10
3 6d 9
C
4 C
3 9
10
6
5
4
3
Act ND
days
Pred CD
days
NC
u
CC
u
Crash
Days
Crash
Cost /
day
A 5 - 3 250 300 2 25
B 4 A 3 300 375 1 75
C 6 A 3 350 875 3 175
D 3 B,C 2 300 350 1 50
0 12
0
0 1
13
2
Step 2: Crash the critical path
ACD.
Options available to crash
A= u 25
C= u 175
D= u 50
Crash A by 1 day: Cost = u 25
(A cannot be crashed any further)
Still the critical path is ACD (12 days)
ABCD Project Crash Duration - 12 days
13. 3 4d 7
B
9
3d
A
3
9 2
3d
D
9
3 6d 9
C
3 9
5
3
Act ND
days
Pred CD
days
NC
u
CC
u
Crash
Days
Crash
Cost /
day
A 5 - 3 250 300 2 25
B 4 A 3 300 375 1 75
C 6 A 3 350 475 1 125
D 3 B,C 2 300 350 1 50
0 11
2
Step 3: Crash the critical path
ACD.
Options available to crash
A= u 25
0 11
(A cannot be crashed any further)
C= u 175
D= u 50
Crash D by 1 day: Cost = u 50
(D cannot be crashed any further)
Still the critical path is ACD (11 days)
ABCD Project Crash Duration - 11 days
14. 3 4d 7
B
9
8
3d
A
3
8
9 2d
D
8
9
3 5
6d 9
8
C
3 9
8
5
4
3
Act ND
days
Pred CD
days
NC
u
CC
u
Crash
Days
Crash
Cost /
day
A 5 - 3 250 300 2 25
B 4 A 3 300 375 1 75
C 6 A 3 350 475 1 125
D 3 B,C 2 300 350 1 50
0 11
0
0 11
0
ABCD Project Crash Duration - 10 days
Step 4: Crash the critical path ACD.
Options available to crash
A= u 25 (A cannot be crashed any further)
C= u 175
D= u 50 (D cannot be crashed any further)
Crash C by 1 day: Cost = u 175
Still the critical path is ACD (10 days)
15. 3 4d 7
B
7
8
3d
A
3
7
8 2d
D
8
7
3 5
4d 8
7
C
3 7
8
3
4
3
Act ND
days
Pred CD
days
NC
u
CC
u
Crash
Days
Crash
Cost /
day
A 5 - 3 250 300 2 25
B 4 A 3 300 375 1 75
C 6 A 3 350 475 1 125
D 3 B,C 2 300 350 1 50
0 1
90
Step 5: Crash the critical path ACD.
Options available to crash
A= u 25
0 1
90
(A cannot be crashed any further)
C= u 175
D= u 50 (D cannot be crashed any further)
Crash C by 1 day: Cost = u 175
Both ABD & ACD are Critical (9
days)
ABCD Project Crash Duration - 9 days
16. 3 4
3d 6
7
B
7
6
3d
A
3
6
7 2d
D
7
6
3 4
3d 6
7
C
3 7
6
3
4
3
Act ND
days
Pred CD
days
NC
u
CC
u
Crash
Days
Crash
Cost /
day
A 5 - 3 250 300 2 25
B 4 A 3 300 375 1 75
C 6 A 3 350 475 1 125
D 3 B,C 2 300 350 1 50
0 8
9
0 8
9
Step 6: Crash the critical path ACD
& ABD.
Options available to crash
A= u 25 (A cannot be crashed any further)
C= u 175 & B= u 75
D= u 50 (D cannot be crashed any further)
Crash C & B by 1 day: Cost = u 250
MAX CRASH
ABCD Project Crash Duration - 8 days
17. Crashing Cost - Summary
2000
1750
1500
1250
1000
7 8 9 10 11 12 13 14 15
Project Duration days
Project
Direct
Cost
u
Step
No.
Project
Duration
days
Activity
Crashed
Crash
Cost
u
Cumulat
ive
Crash
Cost u
Total
Project
Direct
Cost u
0 14 None 0 0 1200
1 13 A by 1 25 25 1225
2 12 A by 1 25 50 1250
3 11 D by 1 50 100 1300
4 10 C by1 175 275 1475
5 9 C by 1 175 450 1650
6 8 C & B by 1 250 700 1900
18. 11
2000
Effect of Crashing on Direct cost
1900
1800
1700
1600
1500
250
In later stages, when
multiple paths are tied
(larger cost slope).
175
In the early stages of
1400
1300
175
50
compression (lesser cost
slope).
1200
25
25
1100
1000 Project Duration days
7 8 9 10 11 12 13 14 15
Project
Direct
Cost
u
19. INDIRECT COSTS
Project overhead
Staff, manager, project engineer salary.
Office equipment and temporary utilities like
electricity, phone.
General overhead
Main office expenses- rent, maintenance.
Site equipment and vehicles.
Lawyers and accountants, Advertising and Social activities.
Contingency fees
Additional cost allocated for unknown events.
Not directly related to activities 12
20. Effect of crashing on Indirect cost
These expenses are
constant for each day
of the project
When the project
duration is decreased
total indirect cost will
decrease
13
Total Overhead Cost
21. Total Project Cost – Direct + Indirect
Ste
p
No.
Project
Duration
days
Activity
Crashed
Crash
Cost
u
Cumul
ative
Crash
Cost u
Total
Project
Direct
Cost u
Indirect
Cost /
day
Total
Indirect
Cost
Total Cost
(Direct +
Indirect)
0 14 None 0 0 1200 100 1400 2600
1 13 A by 1 25 25 1225 100 1300 2525
2 12 A by 1 25 50 1250 100 1200 2450
3 11 D by 1 50 100 1300 100 1100 2400
4 10 C by1 175 275
1475 100 1000 2475
5 9 C by 1 175 450
1650 100 900 2550
6 8 C & B by 1 250 700
1900 100 800 2700
14
23. Steps for Crashing
• Identify activities on Critical path(s)
1
• Compare unit cost of crashing (critical) activities/combinations
2 available for crashing*
• Select activity/combination with minimum unit cost. In case of a
3 tie activity which influences more paths.
• Reduce duration of activity/ combination. (ensure no other path
4 becomes critical if duration reduction is by more that 1 day)
• Recalculate network parameters and go to Step-1.
5
16
*Repeat Steps until activity/combination cannot
undergo further crashing