Project Crashing Department of Industrial Engineering Faculty of Engineering Chiang Mai University
Project Crashing
Crashing is reducing project time by expending additional resources Crash time is an amount of time an activity is reduced Crash cost is the cost of reducing the activity time Goal is to reduce project duration at minimum cost
Project Crashing
N Chareonchai, T Anantana
2
Step of Crashing Project
Determine Allowable Crash Time and Crash Cost Start crashing with the lowest crash cost in the critical path Recheck the critical path - only 1 critical path - more than 1 critical path
Project Crashing
N Chareonchai, T Anantana
3
Housebuilding Network Activity times in weeks
3
1
12
0
8
2
4
4 4
6
12
4
7
4
5
Project Crashing
N Chareonchai, T Anantana
4
Normal Activity And Crash Data Activity
Normal Time (wks)
1-2* 2-3* 2-4 3-4 4-5 4-6* 5-6 6-7*
Project Crashing
12 8 4 0 4 12 4 4
Crash Time (wks) 7 5 3 0 1 9 1 3
Normal Cost $3,000 2,000 4,000 0 500 50,000 500 15,000 $75,000
Crash Cost $5,000 3,500 7,000 0 1,100 71,000 1,100 22,000 $110,700
N Chareonchai, T Anantana
Total Allowable Crash Time (wks) 5 3 1 0 3 3 3 1
Crash Cost per Week $400 500 3,000 0 200 7,000 200 7,000
5
Normal And Crash Relationships $ 7,000 6,000
Crash cost
5,000 4,000
Normal cost
Crashed activity Slope = crash cost per week Normal activity
3,000 2,000
Crash time
1,000 0
Project Crashing
2
4
6
Normal time 8
10 12 14
N Chareonchai, T Anantana
Weeks
6
Network With Crashing Costs Activity 1-2 can be crashed a total of 5 weeks for $2000 Crash cost per week = Total crash cost/Total crash time = $2,000/5 = $400 per week Project duration = 36 wks
3 8
1
12 $400
2
$500 4 $3,000
0
4 $200
12 $7,000 4 4
6
4 $7,000
7
$200
5
Project Crashing
N Chareonchai, T Anantana
7
Crashing Solution Activity 1-2 2-3 2-4 3-4 4-5 4-6 5-6 6-7
Project Crashing
Normal Time (wks) 12 8 4 0 4 12 4 4
Crash Time (wks) 7 5 3 0 1 9 1 3
Crash Time Used
Crash Cost per Week
Crashing Cost Incurred
5 3 0 0 0 3 0 1 12
$400 500 3,000 0 200 7,000 200 7,000
$2,000 1,500 0 0 0 21,000 0 7,000 $31,500
N Chareonchai, T Anantana
8
Crashed Project 8
Project duration = 24 wks
3
5
0 12
1
2
Original time
Project Crashing
12
7
6
4
4
4
9
4
Crashed times
N Chareonchai, T Anantana
3
7
4
5
9
Time-Cost Relationship
Crashing costs increase as project duration decreases Indirect costs decrease as project duration decrease Reduce project length as long as crashing costs are less than indirect costs (optimum cost)
Project Crashing
N Chareonchai, T Anantana
10
Time-Cost Tradeoff Minimum cost = optimal project time
Total cost
Cost ($)
Indirect cost
Direct cost (Crashing cost) Crashing
Time
Project Duration Project Crashing
N Chareonchai, T Anantana
11