Critical Chain Project Management

Hi Pethanna

http://en.wikipedia.org/wiki/Critical_chain_project_management 

This will answer all your questions.

Best regards

Mike Testro

Thanks Mike, i'm already reading thu the page...

as i read along, following query arises:

how much buffer we should consider in a chain?

in conventional planning, i put up the buffer for each of my activity based on the difficulty / risks anticipated.

now for a chain, how do i consider the buffer? one of my friend suggests to go for 30% buffer. but none of the acitivities complete within this buffer, at least in the cases i  have seen so far.

invariably, students syndrome prevails (even if people are unaware of it) which may force me to take 100% buffer for the chain. if i need to consider 100% buffer for feeder chains, then i feel there is no point in drawing a schedule.

if you have been practising on CCPM, what is your experience with % buffer? it will be very helpful if you share.

regards

Pethanna.

Might be of interest.

http://www.spiderproject.ru/library/pmie01_rcp.pdf

Hi Pethanna

I have never bothered with CCPM but with normal CPM I would consider a buffer to be the difference between contract completion and planned completion - whatever that period is.

I prefer to have one buffer at the end of the programme but others prefer to place some at different locations.

Either way is fine.

Asta PowerProject is the only software that I know of that creates a true buffer task.

Best regards

Mike Testro

Hi Pethanna,

CCPM you can do with any software - even without.

Size of buffer depends on the risk of your project, You estimate best guess with an optimistic approach. Unfortunately later your planning will be compared with reality. Maybe you'll make a copy of your plan and change the durations to worst (realistic!) case. So you have a difference e.g. 3 months. It would be possible to create buffer-activities spread over the project - e.g. end of each phase - or one at the end.

But: if you'll use worst case and plan mobilization three month too long this may cost some millions and your boss will accuse you to waste money.

With CCPM it will be easier to discuss the buffer's duration and to get an approval.

Be careful: Many managers tend to delete buffer activities because due to their management project will just need minimum time. Check e.g. during lunch time or other scmall talks what they are thinking.

The last item makes CCPM so difficult.

To avoid student syndrom's effect: No activity longer than two reporting periods apart from manufacturing-/lead-times and level of efforts/hammocks.

Good luck!

Dieter

Mike,

why do you need buffer activity if a buffer is the difference between contract completion and planned completion - whatever that period is?

Best Regards,

Vladimir

Vladimir,

I believe there is a risk of delaying the resource leveling if you create a Milestone activity that is projected to finish after the projected completion time before leveling. In this way you tell the software there is ample time to resource level. Am I wrong?

If I am right can there be the possibility that Asta Buffer Activities can delay resource leveling compared to a schedule without the buffer activities? Maybe it works different to Mike's suggestion.

Rafael

PS Reminds me my request for date markers that in no way can delay resource leveling.

Hi Vladimir

It fills the gap with a visible bar so that the contratctor can lay claim to it when needed.

Particularly relevant with the NEC family of contracts.

Does Spider have a facility to turn a task into a buffer?

Best regards

Mike Testro

Hi Rafael

Asta buffers are consumable - so there is no conflict with other programme processes such as resource levelling.

(Note to all other PP subscribers - whatever Rafael says never ever let the software level your resources)

You get a warning on reschedule if any particular buffer is used up.

Best regards

Mike Testro

Mike,

But you suggested using a milestone and if it comes out to be your last activity on the schedule this can make the software believe it can distribute the activities within the project duration as determined by the last activity in the schedule.

About particular buffers seems to me it is too much for the Americans;

At home, Puerto Rico a US Territory we are lagging with regard to the UK and management of float, only a single buffer [Project Float] is starting to be accepted. Still some specifications that require you to submit a CPM that consumes all available time are included in some contracts, here the Government is notorious. Some cowboys with license to kill can still issue such specifications. They still do not know about Parkinson Law.

Althoug you might argue [and I could agree] that intermediate contractual milestones do have their individual project float I would like to see a reference to a succesful claim in the US regarding a particular intermediate Milestone on a job where the total project duration was not delayed by the Owner, where no extended overhead can be claimed. Yes no extended overhead can be claimed but if the contractor missed the milestone LD's would be applied on the milestone.

I do not see much value to Buffer activities, in any case a distraction. There is no need to use such activities to present a Delay claim something conventional activities can handle very well. With the proper use of date constraints you can see criticality and make your claim. Of course I mean good software implementation of constraints that will show critical path without generating negative float, a value that under resource constraining means nothing, a flawed calculation as implemented in software that promotes the calculation.

Rafael

 Hi Raphael

"But you suggested using a milestone and if it comes out to be your last activity on the schedule this can make the software believe it can distribute the activities within the project duration as determined by the last activity in the schedule."

This is one good reason why you should never let the software level resources.

There are many more.

Best regards

Mike Testro

Mike,

Most or perhaps none of the non optimization algorithms do not use last activity finish, they will never yield the shorter duration you get with optimization methods.

• If your software is not providing for an optimization option maybe nothing is lost.

But I use software that provides optimization options and although I mostly use "prior version" option, only when in trouble I am in need to use the optimization option at the expense of changing the activities sequence, something you must keep under control.

• If your software is not providing for "prior version" functionality then avoid the software leveling your jobs, the PM will be driven crazy after every update, not to mention the rest of the team.

Rafael

Mike,

why may we need to turn a task into buffer?

Spider buffers look like this: It looks like you never used the software that can hep with leveling resources.

Bad luck!

Best Regards,

Vladimir

We tried to use CCPM in P6.

In the end, the project end buffer becomes a management buffer approximately 1 to 2 months or 50% of the floats allowable.

In same cases, the various department will ask for 1 buffer respectively for department-level control.