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Mandatory or Early constraint...

7 replies [Last post]
Tue, 2006-06-27 03:23
Nicolas Berger
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Groups: Petro-Chem / Oil & Gas
Hi everyone,

I’d like to know practically for what reason we should use Mandatory Contraints ?
I have always used Early constraints...

My sub-contractor has given me a schedule (1000 activities)with a least 50 Mandatory constraints...how to consider this knowing that those milestones are not contractual ?

What should I suggest to my Subcontractor as comments ?

Thanks by advance
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Replies

Tue, 2006-06-27 10:22
#1
Nicolas Berger
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Groups: Petro-Chem / Oil & Gas
Thanks Nigel !

Actually it could mean that my sbucontractor is keeping some float in his pockets or maybe (and I think that’s the case) he’s a bit confused in his sequence of scheduling.

Thanks anyway guys for your participation !
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Tue, 2006-06-27 10:16
#2
Nigel Winkley
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Nicolas

From your reply, it sounds like the contractor has ’forced’ his programme to meet the end date. Without the constraints, it finished earlier. This PROBABLY means that he has a lot of float that he is hiding - or making an allowance for lateness.

Done similar things but not with mandatory constraints.

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Tue, 2006-06-27 08:21
#3
Paul Harris
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Nicolas

I would like to clarify what a Mandatory constraint does to a P3 schedule.

A Mandatory constraint stops float (negative or positive) calculating through the task with the mandatory constraint.

A Mandatory constraint in the middle of a chain will break the chain and the float calculations will start again at the constraint. Normally this is not a good practice.

Paul E Harris
Eastwood Harris Pty Ltd, Melbourne, Australia
Planning and Scheduling Training Manual & Book Publishers & Consulting
www.eh.com.au
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Tue, 2006-06-27 04:24
#4
Nicolas Berger
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Groups: Petro-Chem / Oil & Gas
So I removed all those "Mandatory constraints"...they all had predecessors...
But result is, the sequence has changed and Finish date is 2 month earlier.

And all those milestones are now spread out.
This schedule must be rework...
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Tue, 2006-06-27 03:54
#5
Nigel Winkley
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Bon Chance
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Tue, 2006-06-27 03:44
#6
Nicolas Berger
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Joined: 12 Jun 2006
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I Understand and I am agree !

Thanks, I’ll check it out right now...
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Tue, 2006-06-27 03:38
#7
Nigel Winkley
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Nicolas

A mandatory constraint is not as flexible as an early constraint. A mandatory constraint will affect the programme logic a lot more than an early constraint.

If your contractor has used that many mandatory constraints it suggests that there is a problem with his logic and he is using the constraints to ’force’ the logic to work.

If it was me, I would make a copy, remove a section of the constraints and re-schedule. See how far out his logic is.


I generally use two mandatory constraints - Project Start and Project Finish and then only to force the float.

Cheers

Nige
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