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P6 - Critical Path & Separable Portions

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David Lamont
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Hi there. I am hoping someone can solve a conundrum I am facing.

I have a project that has 3 Separable Portions, somewhat interrelated, but each with their own contractual end date. The program has approx. 1000 activities, all leading towards the Project Completion Milestone.

When the Critical Path is calculated the Float is calculated based on the completion of the final (latest finishing) Separable portion. Therefore, Total Float on the program is displayed for all activities, (even those outside of this Portion of works) relative to the end date of the final separable portion – being the PC date for the project.

The project manager wants to know which activities within each Separable Portion are the most critical to that specific Separable Portion’s completion. IE which activities he needs to focus on in order to meet his Separable Portion completion dates (to avoid LD’s). Given the delay to completion of one SP has no bearing (mostly) on the completion of the other, total float is, at least contractually, quite meaningless.

Ideally we could choose to identify the critical patch between two activities - activity X say ‘Site Access’ and activity Y say ‘Sep Portion 2 Completion’. Filter by SP2 and we have a printable program with the CP displayed for that potion and float shown relative to this SP2 completion date. In other words, show the critical path between these two activities only.

For each SP, we can simply identify an end date applicable to the CP calculation and bingo… job done.

I have been doing some research around Multiple Float paths and trawling around P6 sites without much success. Without creating multiple programs, is anyone aware of a possible solution?

Thanks very much.

Dave.

Replies

Zoltan Palffy
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glad I could help like you said not ideal but it gets you what you want and thats the bottom line

Mike Testro
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Hi Dave

Alternatively you can just put a Finish on or After constraint on the end of each section.

Better still use Asta PowerProject where you can reschedule each section in isolation and show the inividual critical path.

Best regards

Mike Testro

David Lamont
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Joined: 26 Jun 2017
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Thank you very much... greatly appreciated.

Not an ideal solution, but it works..

Cheers and thanks.

Dave.

Zoltan Palffy
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follow this order or you will have ot do this again

create a new activity code all it Tracking now give it 3new code values 

SP1 Sep Portion1

SP2 Sep Portion2

SP3 Sep Portion 3

create another activity code call it SharedTrack now give it a code value of 

SHA Shared Portions

now add these two codes as columns

Now in the predecessor window right click and modify it and make sure that driving and critical is selected

now filter for ONLY the LAST actvity in the SP1 grouping 

now look at its predecesor and look for the activity that is driving and critical or at least driving now clikc on that predecessor and at the bottom click GOTO keep doing this until you get back to the data date. 

Now in the column labeled as TRACKING put the code of SP1 into the top of that column 

Next do a fill down for all of those activities this is your SP1 path now you can create a filter for this path

do the same for SP2 and SP3

while you are tracing back paths SP2 and SP3 if the activity already has a value in the TRACKING column DONOT populate the TRACKING column but instead in the SharedTracking code assign the SHA code to this actviity.

Now you can filter for SP1, SP2 or SP3 or all three or a combination of either.

If you did use the SHA code then when you filer for SP1 SP2 or SP3 just add another filter or add that to the SP filter

so the filter for SP1 with a shared activity would look like this 

Any 

where Tracking equlas SP1

or 

where  SharedTrack is not equal to (leave this part blank)

 

I know its a pain but should not take more than a couple of minutes to do. 

 

 

 

Tom Boyle
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Hi Dave,

In my opinion, the simplest approach for a one-off analysis is to temporarily add a super-long trailing dummy activity as a successor to each of your "SP" key completion milestones.  This is the "trailing-dummy" approach that has been around for decades.  You make the dummy activity long enough to 1) Artificially force the key completion milestone and all of its driving predecessors onto the Longest Path; and 2) Artificially inflate the Total Float of the unrelated activities (provided they are not otherwise constrained) high enough to differentiate them from the driving and near-driving paths of interest.  Make a separate UDF and run a global change to save normalized float values for each of the key milestones.  Then remove the dummy activity.  Using the UDFs, you can make separate layouts to filter, group, and sort activities driving each key milestone.

An alternate ("super-constrained-milestone") approach - useful when there are multiple contractual constraints in the schedule - is to assign an FOB constraint (to each SP completion milestone independently) with a date that is 100-300 days in advance of the scheduled early date, then re-schedule.  This approach will impose substantial negative float along the driving and near-driving paths to the milestone being evaluated.

If your project uses multiple calendars (and most do nowadays), then total float can change along a single logical path. In that case, the trailing dummy approach will accurately define the critical path but will no longer be 100% reliable for differentiating near-critical paths.  The super-constrained milestone approach will reliably identify neither critical nor near-critical paths to the milestone.  Here are a few options:

  1. Use multiple-float-path analysis with free float option to identify the driving and near-driving paths to each milestone. In my experience, this is as reliable as the trailing-dummy at correctly identifying the driving path to each milestone, while avoiding the potential hazard of leaving "temporary" changes in the schedule. ("Relative float" of each path is not computed but may be manually estimated.)
  2. Look for an add-in that computes "Longest Path Value" for key completion milestones.  I think Schedule Analyzer does it.  This would provide the benefits of MFP while also computing the amount of "relative float" in the near-driving paths.

Good luck, t