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when a successor starts before its predecessor ... ...

4 replies [Last post]
Forrest Chen
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Joined: 29 Dec 2011
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Hi there,

Now I am having a problem which has been killing my brain cells for the past few days.

when I was trying to update my schedule in P6, I found out that in reality, some of the work sequence has changed, successor started before its predecessor, when I update accordingly, the gantt chart looks weird (there are blank/space in a bar )and the durations become incorrect. any solution will be highly appreciated, thanks.

 

Forrest

Replies

Gary Whitehead
User offline. Last seen 1 week 5 days ago. Offline

Forrest,

 

When you update, don't just update the actual start / finish, also update the relationships to reflect what actually happened.

(NB: You should also investigate to understand why your original sequence was not followed -was the original relationship wrong? were you using relationships to balance resources? Is the project operating at higher risk to save time?) 

This will fix your problem regardless of whether retained logic or progress overide option is used, and is considered best practise for planning professionals.

 

Cheers,

 

G

mahmoud el shamy
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Joined: 10 Feb 2012
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hi forrest

the primavera calculate the schedule according to the relation you inserted at the beginning but when you make update sometimes your relations wers wrong and some successors start before predesseccors so the program doesnt care about this something and run the schedule as the remaining % of this successor will stop untill the relation apply

so you will find gab or the end of this activity will not be correct if you estimated as(data date + remaining duration)

best regards

mahmoud el shamy

Rafael Davila
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Joined: 1 Mar 2004
Posts: 4748

Forrest,

This is known as out-of-sequence progress, use the term to search literature on it. Most probably you are using the retained logic option.

How the software handles out-of-sequence depends on the available options provided by your computer. Retained logic gives extreme results but viable while progress override might seem like it is, but usually it is not. As a matter of fact usually a mere change in lag value will correct logic. Other times links must be changed, usually when a FS link is broken you can opt to change it to a SS relationship with lag plus a FF relationship as the original FS relationship implies. Another option would be to split the predecessor activity into two as to model the plan using FS logic but it adds an activity that will create issues at the time of comparing against a baseline that do not have such split.

Best regards,

Rafael

Mike Testro
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Joined: 14 Dec 2005
Posts: 4387

Hi Forrest

Check for must end by constraints.

Best regards

Mike Testro