Negative Total Float Issue
- Created
- 25
- 6
My project has about 3000 activities and has a strange case. Three activities in a row (Act A then Act. B, then Act. C) without any constraints and their Total Float is as follow
Act. A: TF=-1
Act. B: TF=15
Act. C: TF=-1
I wonder if there is an explanation of that case knowing that nothing else is linked to Act. B. I am using P6
25 replies
Oldest first- 0Mike Testro ·Hi Mo He
You do not explain the logic links between the three activities - are they FS with no lags?
There could be constraints further down the line.
Or maybe there are conflicting calendars or work patterns.
Filter & check the whole critical path to isoltae the problem.
Best regards
Mike Testro
- 0Mike Testro ·Hi Mo He
If you are sure that there are NO constraint flags enywhere on your project then check:
1. Does your calendar extend beyond the work end?
2. Do any resources have different calendars?
3. Are there any link loops in the logic?
4. Have you put in any progress on down stream activities?
Otherwise you have a software glitch.
Best regards
Mike Testro. - 0Mohamed Hegab ·The activities have no progress whatsoever. There are some constraints in the project but not in these activities. The project is not resource loaded. There may be progress in activities downstream but how it would affect those simple sequenced activities. I emailed the problem to Primavera and they are researching but didn’t give me a clue yet. I have this issue in several locations in the project but this is the case that has no doubt.
Thanks,
Mo - 0Mike Testro ·Hi Mo He
The two negative float activities must be showing critical.
Filter on critical activities - or even super critical - and you may get a clearer view of the problem.
It is most likely a "must end on" constraint down stream of the problem activities.
Alternatively just take ALL contraints off and re-schedule.
Best regards
Mike Testro - 0Paul Harris ·Did you import them from some where else and have the been assigned a External dates, which acts like a constraints.
Show the External date columns to check.
Paul E Harris
Eastwood Harris Pty Ltd, Melbourne, Australia
Planning and Scheduling Training Manual & Book Publishers, Consulting and Training
www.eh.com.au
www.primavera.com.au
- 0Velmon Capanayan ·Dear All,
Im having the same problem.
I just establish a schedule, and im presently reviewing my logical links. I just observe that my critical activities are negative floats and equal to the total durations of the project. Normally the critical activities should be zero, if the ’must finish by’ is not set. Please help me on this, may be in initial set up it requires some options to do the calculation of float.
Hoping for immediate response.
Thanks,
Velmon
- 0Rafael Davila ·Mo He
I know you said that the activities have no progress whatsoever. But I would like to rule out the possibility this is caused by out-of-sequence events.
Check in the out-of-sequence report if any of these activities are listed as being out-of-sequence.
If any is listed as out-of-sequence this might be the cause as a common reason for negative float is out of sequence activities, sometimes referred to as broken logic. This often occurs if the schedule has been part progressed and actual dates have been added.
If you set an actual start date with 0%progress this is in CPM terms an activity with progress and this might still be able to cause an out-of-sequence event.
Also if you set a successor to these activities with an actual start, again even with 0%progress this might also cause these activities to be out of sequence.
First you got to rule out out-of-sequence then if occurs you got to find why.
Best regards,
Rafael - 0Shah. HB ·Mr.Rafael initially when baseline is prepared normally it wont have negative total float except introduction of must finish dates.then on scheduling total float becomes -ve due to actual dates and % of completion introduction? or is there any other reason for negative total float?
- 0Rafael Davila ·Shahul
Baseline Schedules should never show negative float in any case some positive float as use of buffers should be allowed; unfortunately use of buffers is not a widely accepted practice in my location, in occasions prohibited by some specs.
The only reasons I can think of at this moment for a schedule to show negative float are the effect of constraints (internal and/or external) or the effect of out-of-sequence progress.
Your statement - I guess use of negative float is not recommended by Consultant and delay analyst, but I have no idea about it. – is supported by some specifications that prohibit the use of negative float as a basis for EOT claims. With a Google search you can get plenty of samples.
Best regards,
Rafael - 0Velmurugan Selvan ·
Hi, This will solve your
Hi,
This will solve your problem "Negative Float in the critical path"
When you apply "Must Finish By" constrain to the project finish date, primavera will default to take the project end date and time as 12:00 AM regardless to date, that's the reason it shows the Negate float.On ground the project end by the end of the day depending up on the project & type, let we assume the project will end by 4:00 PM.
Now enable time hour units in User preference and see the project end date and hours, e.g. 24 May 2011 4:00 PM, now set the must finish date to 24 May 2011 12:00 AM (which primavera assumes default) to 24 May 2011 4:00 PM, schedule the project.
Nowyou can see the critical path without negative float.
If the problem is not fixed by the above means, then the project links & scheduling options to be checked.
Cheer up............. - 0Cezar Comoda ·
Hi Buddies, My problem is
Hi Buddies,
My problem is related to the above maybe you can advice me also, the scenario is predecessors had 100% complete and successor something around 30~60% progress then followed by no progressed successors, the on progress activities has avery huge TF which is longer than project duration where as the not progressed successors only shows 2 months of TF.
Zeggie
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