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Project Crashing

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

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Project Crashing

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  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 subcontractors • Often introduces unanticipated problems • The faster an activity is completed, the more it costs • There is always a lower bound on task duration 9/20/2014 Ardavan Asef-Vaziri 6-1

  2. Cost Crash point Crash cost = Normal point Normal cost = Time Crash time = Normaltime = Linear Time / Cost Tradeoff Slope (bj) = increase in cost from reducing task duration by one time unit 9/20/2014 Ardavan Asef-Vaziri -4

  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. • Find the critical path or paths • If there is no other critical activity which could still be reduced, and shorten the critical path. Stop. • Crash the cheapest critical activity (or combination of activities) to shorten the critical path (or paths) by one day. • Go to 1 9/20/2014 Ardavan Asef-Vaziri -5

  4. Project Crashing Example 9/20/2014 Ardavan Asef-Vaziri -4

  5. 21 Days Network and Its Total Cost c f a d g b e 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 9/20/2014 Normal Cost = 60+50+100+30+70+40+50 = 400 Ardavan Asef-Vaziri -5

  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 9/20/2014 Ardavan Asef-Vaziri 6

  7. 21 to 20 Days Network c f a d g b e 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 9/20/2014 Normal Cost = 400 + a(30) = 430 Ardavan Asef-Vaziri -7

  8. 20 Days Network 1 9/20/2014 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. Ardavan Asef-Vaziri -8

  9. 20 to 19 Days Network c f a d g b e 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 9/20/2014 Ardavan Asef-Vaziri -9

  10. 19 Days Network c f a d g b e 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 9/20/2014 Normal Cost = 430 +c(30) =460 Ardavan Asef-Vaziri -10

  11. At 19 Days All are Critical 1 1 9/20/2014 All activities on CP, do not think of e-b because of d-a Activities a-c-f, andd-g are on the critical path a and d cannot be crashed any more gandone of c-fand c30, f40 g60 c and g Ardavan Asef-Vaziri 6-11 -11

  12. 19 To 18 Days Network c f a d g b e 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 9/20/2014 Ardavan Asef-Vaziri -12

  13. 18 Days Network f c a d g b e 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 9/20/2014 Normal Cost = 460 + c(30) + g(60) =550 Ardavan Asef-Vaziri -13

  14. At 18 Days All are Critical 1 2 1 9/20/2014 f40, g60 Ardavan Asef-Vaziri 6-14 -14

  15. 17 Days Network c f a d g b e 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 9/20/2014 Ardavan Asef-Vaziri -15

  16. From 17 Day To 16 1 2 1 2 9/20/2014 Ardavan Asef-Vaziri -16

  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. 9/20/2014 Ardavan Asef-Vaziri 17

  18. 16 Days Network c f a d g b e 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 9/20/2014 Ardavan Asef-Vaziri -18

  19. Trade-off: Cost-Time 9/20/2014 Ardavan Asef-Vaziri -19

  20. Assignment 1: Crash the Following Network. Prepare Cost-time Curve 9/20/2014 ArdavanAsef-Vaziri -20

  21. Prepare Cost-Time Curve 9/20/2014 ArdavanAsef-Vaziri -21

  22. 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 9/20/2014 Ardavan Asef-Vaziri -22

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