project crashing
DESCRIPTION
Project Crashing. Crashing means shortening duration of activities Because some activities were delayed Or client is willing to pay more for earlier completion Crashing changes the schedule for remaining activities It has impact on schedules for all the subcontractors - PowerPoint PPT PresentationTRANSCRIPT
6-1
Project Crashing
Crashing means shortening duration of activities Because some activities were delayed Or client is willing to pay more for earlier completion
Crashing changes the schedule for remaining activities It has impact on schedules for all the subcontractorsOften introduces unanticipated problemsThe faster an activity is completed, the more it costsThere is always a lower bound on task duration
04/21/23 Ardavan Asef-Vaziri 6-1
6-2
Linear Time / Cost Tradeoff
Time
Cost
Crash point
Normal point
Normal time =Crash time =
Normal cost =
Crash cost =
tjNtj
c
Cjc
CjN
Slope (bj) = increase in cost from reducing task duration by one time unit
Time Normal - TimeCrash
Cost Normal -Cost Crash Slope
04/21/23 Ardavan Asef-Vaziri -4
6-3
Crashing Algorithm
Assume each task can be crashed one day at a time (simplifying assumption, but not necessary)
Crash Only critical activities. Crashing other activities can only increase cost without changing project duration
To decrease project duration by one day, the critical path or paths must decrease by one day.
1. Find the critical path or paths
2. If there is no other critical activity which could still be reduced, and shorten the critical path. Stop.
3. Crash the cheapest critical activity (or combination of activities) to shorten the critical path (or paths) by one day.
4. Go to 1
04/21/23 Ardavan Asef-Vaziri -5
6-4
Project Crashing Example
04/21/23 Ardavan Asef-Vaziri -4
Activity Predecesor Time(N) Time(C) Cost(N) Cost(C) C/T Lefta - 6 5 60 90 30 1b - 7 4 50 150 33.3 3c a 6 4 100 160 30 2d a 7 7 30 30 - -e b 5 4 70 85 15 1f c 9 7 40 120 40 2g d,e 7 4 50 230 60 3
6-504/21/23 Ardavan Asef-Vaziri -5
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
a
b
c
d
e
g
f
21 Days Network and Its Total Cost
Normal Cost = 60+50+100+30+70+40+50 = 400
6-6
From 21 to 20 Days
a-c-f are on the critical path a and c are the least-cost choice. We crash a because it
affects two paths
04/21/23 Ardavan Asef-Vaziri 6
Activity Predecesor Time(N) Time(C) Cost(N) Cost(C) C/T Lefta - 6 5 60 90 30 1b - 7 4 50 150 33.3 3c a 6 4 100 160 30 2d a 7 7 30 30 - -e b 5 4 70 85 15 1f c 9 7 40 120 40 2g d,e 7 4 50 230 60 3
6-704/21/23 Ardavan Asef-Vaziri -7
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
a
b e
c
d g
f
21 to 20 Days Network
Normal Cost = 400 + a(30) = 430
6-8
20 Days Network
04/21/23 Ardavan Asef-Vaziri -8
1Activity Predecesor Time(N) Time(C) Cost(N) Cost(C) C/T Left
a - 6 5 60 90 30 1b - 7 4 50 150 33.3 3c a 6 4 100 160 30 2d a 7 7 30 30 - -e b 5 4 70 85 15 1f c 9 7 40 120 40 2g d,e 7 4 50 230 60 3
Activities a-c-f are still on the critical path a cannot be crashed any more c is the least-cost choice. Lower c’s normal time by one day.
6-904/21/23 Ardavan Asef-Vaziri -9
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
a
b e
c
d g
f
20 to 19 Days Network
6-1004/21/23 Ardavan Asef-Vaziri -10
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
a
b e
c
d g
f
19 Days Network
Normal Cost = 430 +c(30) =460
6-11
At 19 Days All are Critical
04/21/23 Ardavan Asef-Vaziri -11
1
1
Activity Predecesor Time(N) Time(C) Cost(N) Cost(C) C/T Lefta - 6 5 60 90 30 1b - 7 4 50 150 33.3 3c a 6 4 100 160 30.0 2d a 7 7 30 30 - -e b 5 4 70 85 15 1f c 9 7 40 120 40 2g d,e 7 4 50 230 60 3
All activities on CP, do not think of e-b because of d-a Activities a-c-f, and d-g are on the critical path a and d cannot be crashed any more g and one of c-f and c30, f40 g60 c and g
6-1204/21/23 Ardavan Asef-Vaziri -12
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
a
b e
c
d g
f
19 To 18 Days Network
6-1304/21/23 Ardavan Asef-Vaziri -13
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
a
b e
c
d g
f
18 Days Network
Normal Cost = 460 + c(30) + g(60) =550
6-14
At 18 Days All are Critical
04/21/23 Ardavan Asef-Vaziri -14
1
2
Activity Predecesor Time(N) Time(C) Cost(N) Cost(C) C/T Lefta - 6 5 60 90 30 1b - 7 4 50 150 33.3 3c a 6 4 100 160 30.0 2d a 7 7 30 30 - -e b 5 4 70 85 15 1f c 9 7 40 120 40 2g d,e 7 4 50 230 60 3
f40, g60
1
6-1504/21/23 Ardavan Asef-Vaziri -15
17 Days Network
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
a
b
c
d
e
g
f
6-1604/21/23 Ardavan Asef-Vaziri -16
From 17 Day To 16
1
2
2
Activity Predecesor Time(N) Time(C) Cost(N) Cost(C) C/T Lefta - 6 5 60 90 30 1b - 7 4 50 150 33.3 3c a 6 4 100 160 30.0 2d a 7 7 30 30 - -e b 5 4 70 85 15 1f c 9 7 40 120 40 2g d,e 7 4 50 230 60 3
1
6-17
Crashing- 17,16 Days
We can shorten the project to 16 days by crashing g and f still another day.
The cost of the project is $400+ 30(a) + 30(c2) + 60(g3)+40(f2) = $750
Activities a,c,f, and g have been crashed to their limits. No further crashing will help so b,d, and e remain at their
normal times and costs.
04/21/23 Ardavan Asef-Vaziri 17
6-1804/21/23 Ardavan Asef-Vaziri -18
16 Days Network
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
a
b
c
d
e
g
f
6-1904/21/23 Ardavan Asef-Vaziri -19
Project Crashing
400
450
500
550
600
650
700
750
15 16 17 18 19 20 21
Project Duration
Pro
ject
Co
st
Example 1
Trade-off: Cost-Time
6-20
Assignment 1: Crash the Following Network. Prepare Cost-time Curve
04/21/23 Ardavan Asef-Vaziri -20
6-21
Prepare Cost-Time Curve
04/21/23 Ardavan Asef-Vaziri -21
6-2204/21/23 Ardavan Asef-Vaziri -22
Activity Predecesor T(N) Time(C) Cost(N) Cost(C) C/T Lefta - 6 5 60 90 30 1b - 7 4 50 150 33.3 3[c] a 6 4 100 160 60 2d a 7 7 30 30 - -e b 5 4 70 85 15 1f c 9 7 40 120 40 2g d,e 7 4 50 230 60 3
Assignment 2
The same example as we solved.Activity c either 0 or 2 but not 1. Solve it in the easiest way. Prepare Time-Cost Trade-off Curve