Hey dahnnyz, crashing is easier than it is put out to be you just need to know how to identify the activities that are the most appropriate to crash. But first of all what is crashing?
Crashing is the reduction in the completion time of a project.
The purpose of crashing projects is to save time, not money (although money is budgeted to be minimum). This works by reducing specific activities in the project (could mean employing more workers, purchasing of technologies or what have you). When crashing projects, you generally are required to crash critical activities (in a bid to reduce the overall project time), as the critical path represents the total duration of the whole project. By crashing specific activities, you must look at the whole picture (i.e. all the paths possible) and thereby crashing accordingly.
How2Do?
Say for example you get a diagram as represented at the bottom of this post as well as a question as follows.
Question: Crash the project so that it is reduced by 3 days. The following table of the costs associated in crashing each activity is shown below.
Activity Cost Maximum days available for crashing
A $400 2
B $350 3
E $300 1
H $250 2
K $600 3
G $100 2
Basically follow these steps and you can crash the project:
1) You must first identify the critical path.
The critical path here is A-C-H-K with an overall duration of 43 days.
2) Second, identify all the other paths and their durations
A-D-E-J-K = 42 days
B-F-J-K = 41 days
B-G-L = 38 days
3) The next step is to other paths that are required to crash as a result of crashing the critical path in order to meet the deadline (being 3 days as given in the question)
43 days less 3 days = 40 days
Therefore paths that need to be crashed are A-C-H-K (3 days), A-D-E-J-K (2 days) and B-F-J-K (1 day).
4) Basically now you have to determine two things:
a)the activities that must be crashed and
b)the minimum overall cost
The question may have some activities that don't need to be crashed however it is still listed in the table (eg. Activity G) so they can be eliminated.
The remaining activities are all appropriate activities to crash being A, B, E, H & K; but which activities are cheapest to crash?
This is where you have to weigh the options:
Reducing activity K by 3 days will result to the overall completion time to be reduced by 3 days, at a cost of $1800
Is there a cheaper option?
By reducing K by 1 day, A by 1 day and B by 1 day and H by 1 day, the completion time is reduced at a cost of 600+400+350+250 = $1600, cheaper than the previous option.
Any more options?
Crashing activity H by 2 days, A by 1 day, E by 1 day and B by 1 day will result in the completion of the project 3 days earlier, with a cost of 2(250)+400+300+350 = $1550
..more?..
By now you should have enough practice and be able to realise that crashing activity A by 2 days, H by 1 day and B by 1 day it will result in the cheapest cost of 2(400)+250+350 = $1400
So therefore the overall cost to complete the project 3 days earlier is $1400, and all affected paths are now shortened in compliance with the changes.
I hope this makes sense to you if you have any questions about crashing don't hesitate to ask.
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