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How to create different Critical Path

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Andrea Giordano O...
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hi everybody,

  I would like to do 2 critical path in the same schedule, for 2 different unit in the same plant , how is possible to apply on P6 ?

 

thanks in advance

Andrea  

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Rafael Davila
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As a general rule, every activity in any CPM schedule – except the start and finish milestones – must have at least one predecessor and at least one successor.   Dangling activities not meeting this rule – also known as open-ended activities – indicate inadequate schedule logic.

When you have multiple start and/or multiple finish milestones you will have multiple dangling milestones and the rule might not be broken.  Just make sure every activity, except start/finish milestones are linked to a path leading to the appropriate milestones.

Keep in mind longest path gets broken under resource leveling, constraints, interproject relationships (treated as constraints).  https://docs.oracle.com/cd/E17462_01/Web_Access/Help/en/Projects/Tasks/pm_cpm.htm

  • Longest path defines the sequence of driving activities that determine the project end date.
  • The longest path is broken when activities are no longer driven by relationships; that is, when activity dates are driven by constraints or resource leveling.  Longest path calculation includes interproject relationships. Therefore, activities designated as on the longest path may change depending on whether you schedule a project alone or with its related projects.  If a project has interproject relationships and you schedule it alone, the interproject relationships are treated as scheduling constraints.

Not all project milestones have a target finish date, in such case the finish milestone is not date constrained. If you want to see independent resource critical path for these milestones as well as activities float that will not delay the milestones this setting (make open-ended activities critical) should do it.  

When you set finish date constraints in P6 it can create negative float values, negative float is information that helps to analyze project status but is useless for project network analysis.  The workaround recommended by experienced schedulers in such software is to temporary eliminating the constraints plus other remedial actions that might include setting open-ends as critical.

Primavera P3 users could resort to Zero total float constraint - Use a zero total float constraint to make an activity critical. When you impose a zero total float constraint, P3 sets the late dates for the activity equal to its early dates, giving it zero total float.

P3 had more and better implemented constraint options than P6.  Noteworthy are date constraints only used when they create a tighter schedule. Only nefarious mandatory constraints would create negative float.  Mandatory P3 constraints were used only temporarily for purpose of analysis.

https://docs.oracle.com/cd/E20557_01/documentation/P3/P330ref.pdf

On the other hand Spider Project can display negative float without use of nefarious mandatory constraints or date constraints that would mess with late dates as P6 does.

I wonder if P6 option to make open-ends critical will override date constraints on these activities. 

open-ends-001

Zoltan Palffy
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you can make open end critical but techanically there sould only be 1 open end which is the last activty in the schedule

Rafael Davila
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P6-make-open-ended-activities-critical
Andrea Giordano O...
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Thanks again for your answer, Im just checking reliability of schedule, cause has still to be defined by contract and im preparing tentative baseline.

Zoltan Palffy
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the other option is to change the float value range that determines when something is critical.

In P6 

open your project 

go to the Projects directory and make sure your project is highlighted

Click on the Settings tab

under the section Define Critical Activities

Select Total Float Less than or equal to and then on the right put in the number of days that you want to set that threshold at.

The default is 0 days. 

Andrea Giordano O...
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Thank u very much Zita,

ciao

Andrea

Tom Boyle
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There are several ways to identify multiple critical paths in a P6 project schedule.  https://boyleprojectconsulting.com/TomsBlog/2017/09/16/multiple-critical-paths-in-a-single-cpm-schedule/

Choose one:

  • Multiple Float Paths
  • Super-aggressive late constraint
  • Super-long trailing dummy (with Longest Path).

Good luck, tom

Zita van Beusekom
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Andrea,

Not sure what you mean to create 2 critical path in the same schedule, since critical path is the longest path or one with "limited float", so to attain 1, 2 or more critical paths on same schedule; its better to set constraint date to the last activities of those series of activities  or you can connect the last activity to a common milestones and then the the series of activities with more float than the other you can set a "LAG". This way you know that all these activities belong to your "critical path".

 

In P6 there is an advance option for scheduling, I am not sure if this is what you mean. This gives you an option to have amount of schedule scenario for achieving certain "milestone" (this is advisable if you have a very complex network of activities. This helps planner to focus on certain amount of activities only...>>>i cannot embed a picture to show this but if you have p6, go to schedule (F9), and click on ÖPTION, and second tab is ADVANCED, and there you can opt for Free Float or Total Float calculation for number of paths (series of activities) as you wish.