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Critical path with positive float????

9 replies [Last post]
Sat, 2009-10-24 12:38
WAEL ELHAJJ
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Joined: 14 Feb 2008
Posts: 55
Groups: Petro-Chem / Oil & Gas
dear all,
has it happened with any one that the longest path of the project contains activities with positive flaot???mainly all of the critical path is that of activities which are not critical. on the other hand the critical activities don’t show.
how could this be???
how could it be resolved?
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Replies

Mon, 2009-10-26 13:33
#1
Rafael Davila
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Joined: 1 Mar 2004
Posts: 5241
Groups: Spider Project Team
Must Finish By

After the forward pass, if a Must Finish by Date is specified in the Project Details Dates tab, the backward pass is calculated using the must finish by date rather than the schedule end date.

A Primavera aberration that manipulates computation of float some other software developers followed, the same as many foolish Owners.

Best regards,
Rafael
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Mon, 2009-10-26 12:55
#2
Mike Testro
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Joined: 14 Dec 2005
Posts: 4420
Groups: Building Information Modelling, Content Moderators, GPCCAR Editors
Hi Wael

As Vladimir pointed out this is almost certainly a problem with calendars - as a start I would make sure that all tasks are on the same calendar AND work pattern.

Try lookimg at some of these.

Are there any Lead Lag Links that may be set to Calendar days - if these links end in a holiday you lose all upstream criticality.

Have you allocated resources to the tasks - if so what calendars are attached to the resources?

Is the + float a constant number - if so try setting the criticality to a day more than the float number - that will show you A critical path and maybe where the problem is.

Do you have a completion milestone? If so is it on the same calendar as all the other tasks.

Best regards

Mike Testro
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Mon, 2009-10-26 10:52
#3
Lawrence Cuozzo
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Joined: 13 Apr 2007
Posts: 44
Groups: None
Hey Rafael -

Dude, it’s like CheeCH & Chong man, not Cheek & Chong. And dude, for your information, they were not just like in the 70s, man. They are currently on their "Light Up America" tour, dude.

Peace, love and positive float man,

Lawrence
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Sun, 2009-10-25 08:51
#4
Vladimir Liberzon
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Groups: Accreditation Editors, Board of Advisors, Civil Engineering, GPCCAR Editors, Petro-Chem / Oil & Gas, Regional Representatives, Spider Project Team, TURNAROUND & SHUTDOWN (T/A & S/D)
Wael,
I had sent to you my E-mail address in private message.
Best Regards,
Vladimir
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Sun, 2009-10-25 08:23
#5
Rafael Davila
User offline. Last seen 2 weeks 2 days ago. Offline
Joined: 1 Mar 2004
Posts: 5241
Groups: Spider Project Team
WAEL ELHAJJ

Have you checked on the project properties or overview if there is a specified date for the job end, a must finish by date, this is a Constraint that also affect the backward pass computations.

I don’t have P6 but this is functionality on all Primavera software, a functionality I dislike and wish Primavera never provided with their software, is a manipulation on the definition of float that most probably is already driving you crazy.

By the way, Cheek and Chong were two movie characters of the 70,s that smoked pot and were always stoned, their behavior never make any sense similar to the behavior of a CPM when constraint dates are applied to the backward computations. Under these constraints you get all weird things like negative float with the additional complication in the results for float when you apply the constraints to several activities and their chains merge at some point,a total mess only Cheek and Chong at their peak would understand.

If you are not required to use finish constraints that affect the backward pass computation, don’t use them instead use a fixed milestone.

Because Spider Project does not have this aberration of functionality that manipulates backward pass but instead provides you with a milestone flag, he might overlook tha Primavera also provides for constraining at the project level, an aberration of the maximum order.

Best regards,
Rafael
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Sun, 2009-10-25 08:00
#6
Vladimir Liberzon
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Wael,
please check not only finish but also start constraints, please check if all activities and resources use the same calendar.
If no time constraints are applied, the calendar is the same for all activities and resources, and you don’t level resources then you will get Critical path that consists of activities with zero total float.

Best Regards,
Vladimir
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Sun, 2009-10-25 07:47
#7
WAEL ELHAJJ
User offline. Last seen 1 year 48 weeks ago. Offline
Joined: 14 Feb 2008
Posts: 55
Groups: Petro-Chem / Oil & Gas
Dear Rafael,
I have no finish constraint, this is the problem. if i has i could have realized the problem
i neither have constraints nor negative floats, yet i still have on the "longest path" a sequence of activities having 2 weeks positive float.
this is a very strange event. and still i can’t answer my management on the critical path.
a very fast solution is required thus i need any help i could get from every body.
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Sat, 2009-10-24 14:04
#8
Rafael Davila
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The application of a finish constraint date to the backward CPM computations was an invention of a disfunctional mind. In fact two disfunctional minds, CPM gurus Cheek and Chong.

Best regards,
Rafael
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Sat, 2009-10-24 12:58
#9
Vladimir Liberzon
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Groups: Accreditation Editors, Board of Advisors, Civil Engineering, GPCCAR Editors, Petro-Chem / Oil & Gas, Regional Representatives, Spider Project Team, TURNAROUND & SHUTDOWN (T/A & S/D)
It may happen if your schedule has activities with time constraints (Start No Earlier Than, Start Must On), or if there are several calendars.
Just imagine that an activity with 6 days work week with free day on Sunday finished on Friday evening and succeeding activity has 5 days work week with vacations on Saturday and Sunday.
Next activity will start on Monday and it means that preceding activity has one day total float.

It cannot be resolved. I suggest to define as critical all activities with total floats less than ... days.

Best Regards,
Vladimir
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