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Hi!
I am having a hard time inserting relationships especially in determining which should comes next and what type of relationship I will give the two activities.
I was given a sample but all activities are in summary. Meaning for ex. for 20 areas for excavation, in their given data it is the totallity of all the volume for these 20 areas. For its start and efinish date lets consider jan 1 to june 1, 2020
and then the next activity is gravel bedding, same as what i mentioned in the previous paragraph, the datais the total for all of the areas and start and finish date is jan 5 to june 5, 2020.
Should I use same start relationship? Im sorry. I really am confused.
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If an activity is in progress and the progress differs from expected SS relationship shall be updated until the lag is exhausted (required volume was done).
Mr. Vlad,
Now I understand. Thank you!
When the task is now on progress, the SS relationship now becomes driving as well? And should I update relationships each time I update the schedule?
Thank you again!
Yes Russ,
you shall apply both dependencieas.
Gravel bedding can start only after certain volume of excavation was done AND can finish only after Excavation was finished.
Please correct me Mr. Vlad. Are you saying that when applying an SS, I should apply an FF on that activity as well?
Thank you!
"we define FF volume lag as the minimal volume of work that shall remain on succeeding activity when preceding activity will finish."
I like that definition for FF lags.
yes Stephen 4 not 5 fuzzy math
NO RUSS you do not change lags why would you the relationship and the overlap has not changed
Hi Russ,
you did not specify the software that you use but I expect that it does not permit to enter and manage volume lags.
So you shall use time lags for SS and FF dependencies.
In your case link Excavation with Gravel bedding using two links: one is SS with 4 days lag and the second is FF with 4 days lag.
Time lag means that certain amount (volume) of work shall be finished before next activity start and planned duration of this volume execution is 4 days.
Check and adjust your lags manually if excavation will be executed faster or slower than expected.
Mr. Stephen and Mr. Vladimir,
I am sorry, I am not following. It is hard for me to determine SS, SF, and FF usage. I only have basic knowledge, thus, can you explain more. Which should I use then?
Mr. Zoltan,
Does this mean that when I change the schedule, I will also manually change lags?
Steve,
we define FF volume lag as the minimal volume of work that shall remain on succeeding activity when preceding activity will finish.
Hi, Vladimir. You're right, of course, Spider's ability to designate volume lag is useful here.
In my experience, when users are working with software that has only "generic" lag:
1. SS lags almost always model volume lags.
2. FF lags almost always model time lags.
The distinction is relevant for computing drag, where the drag of work modeled in a volume lag is really work that is captured in the predecessor activity. If it's on the CP with 5D of drag, the project may be shortened by 3D by getting the first 100 metres of trench dug in 2d, thus effectively reducing the volume lag to SS+2D.
With a time lag of 5D, it is the lag itself and not the work in the predecessor that has the drag.
Fraternally in project management,
Steve the Bajan
In this case it is right to use volume lag.
Lag Volume is an amount of excavation in pnysical units (cubic meters) that must be done before gravel can begin.
Setting time lag one cannot be sure that required amount will be done in exactly 4 days. For some reasons the planned work may be done slower or faster than expected.
Good explanation, Zoltan. But 4 days lag between start-of Jan 1 and start-of Jan 5.
2 thigs here
1. physically and sequentially the gravel bedding must start AFTER the excavation. It does not have to wait until ALL of the excavation is done to start the gravel but the excavation must be far enough along as not to impede the progress of the gravel.
so logically this will be a start to start realtionship with a lag meaning the start of the gravel will lag behind the start of the excavation.
2. now we have to consider how much to LAG the gravel behind the excavation. In your example based on time the excavation starts on Jan 1 and the gravel starts on Jan 5 the lag would be a start to start with a 5 day lag.
meaning 5 days after the excavation has started then the gravel can begin.
this is how overlapping is done.
Email: PPadmin@planningplanet.com
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