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FF - Relationship

18 replies [Last post]
Thu, 2009-12-10 04:19
Shanmuga Pandian ...
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Is it good to keep FF relationship greater than the original duration of the activity in the schedule?

TN Shanmuga
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Replies

Wed, 2009-12-23 22:34
#1
Rafael Davila
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Mike,

About my posting no 12, no need for a strong link, a hammock with SS and FF relationships both with negative lag will do it.

Negative Lag Hammock

FF relationship with negative lag do it better.

Best regards,
Rafael
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Mon, 2009-12-21 03:41
#2
Anoon Iimos
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Hi Mike,

Comments:

"quote
Various Discipline have input into the DWG .

Civil Engineering Input into Layout
Mechanical Engineering Input into Layout
Piping Engineering Input into Layout
Electrical Engineering Input into Layout
Instrument Engineering Input into Layout.

Not One of these impact the start of the task but effect the completion of the task so then you Use FF logic."unquote

I agree.
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Sat, 2009-12-19 09:51
#3
Rafael Davila
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Mike,

To my understanding all CPM software run their schedule by running a forward and a backward pass, without it there would be no float computation. Therefore all planners use both of them no matter if constraining all activities to ALAP or by inverting the order of the forward and backward computations.

By extrapolation shall I interpret Plan Plan statement as meaning that FS can be used by any planner as well? I accept FS logic as viable as long as it reflects true logic, I even use it over 95% of the time.

Best regards,
Rafael
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Sat, 2009-12-19 09:44
#4
Vladimir Liberzon
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Mike,
I already wrote that it is not correct.
All links are considered on both forward and backward passes.
And in most projects close to 90% of links are Finish to Start.

Best Regards,
Vladimir
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Sat, 2009-12-19 09:04
#5
Mike Testro
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Hi Vladimir

Plan Plan said.

"FS can only be used by planners that use forward pass. Strange but True."

Is this correct?

Best regards

Mike Testro.
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Fri, 2009-12-18 08:48
#6
Vladimir Liberzon
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Mike,
what comments do you expect?
All links are considered in Forward and Backward passes, I see no problem with this.

But you know that I also consider applying both SS and FF links useful in many cases though most project links usually are FS.

I think that links shall reflect true logic, anything artificial shall be avoided.

Best Regards,
Vladimir
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Fri, 2009-12-18 05:57
#7
Mike Testro
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Hi Everyone

I received this private message today in relation to this topic - it does add to the debate with some interesting points.

Good Morning Mike

Do not take this personal but comments like.

"Do not use FF SS links with or without lead lags - it is a lazy planners solution to a simple problem."

Is not good for planning as a Moderator you should know better.

FF link are used by planners that can do a backward pass proper and FS can only be used by planners that use forward pass. Strange but True. It sounds like you have primarily worked on simple project using MS Project based on above comments.

You would notice espacialy on engineering Task that SS FF logic is used. Example

Task 1 = Develop Layout DWG. (Design office Task)
Task 2 = Issue Layout DWG For Comments (FS logic between the two)

Various Discipline have input into the DWG .

Civil Engineering Input into Layout
Mechanical Engineering Input into Layout
Piping Engineering Input into Layout
Electrical Engineering Input into Layout
Instrument Engineering Input into Layout.

Not One of these impact the start of the task but effect the completion of the task so then you Use FF logic.

I can use various examples

Vendor Documents

In Line Installation into Piping etc.

Regards

Any comments?

Best regards

Mike Testro
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Thu, 2009-12-10 11:09
#8
Rafael Davila
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Mike,

The milestone will move following CPM logic, the strong link option prohibits increasing lag between activities.

Is functionality you will only find in Spider Project, probably you can mimic it using some sort of constraints, I dont know, maybe not.

I am in the middle of an estimate but on the week-end will see how it works, it might even be I am wrong as this is new functionality to me.

Best regards,
Rafael
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Thu, 2009-12-10 09:57
#9
Mike Testro
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Hi Rafael

"using a milestone hold in place with a strong link, functionality"

How is that going to affect the critical path?

Best regards

Mike Testro


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Thu, 2009-12-10 08:24
#10
Rafael Davila
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Anoon,

You got it right, I would not get into such granularity, and you know it, I would schedule a single activity spanning a maximum of four weeks because of the scale of nwetwork we are required I do happen to agree with.

The example is merely an exercise. Using Spider Project I would costrict the end of cement paster as to prevent scheduling after epoxy is dry using a milestone hold in place with a strong link, functionality only available in Spider. In this way I would make sure I will get the correct available float.

Strong Link

Best regards,
Rafael
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Thu, 2009-12-10 08:07
#11
Anoon Iimos
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Hi Rafael,

I supposed you can have one activity as "cement plaster with epoxy bonding", you don’t need to separate that so as to use SS relationship.

Or you can break it down into areas of wall, and of course it can be all "FS".

By the way, I like your software with a text window underneath.

cheers
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Thu, 2009-12-10 07:51
#12
Rafael Davila
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Anoon ,

If you are to cement plaster a long wall and epoxy is specified as the bonding agent. How would you model this into CPM logic?

It got to be a continuous flow operation, subdividing into discrete portions would be faulty logic.

Here you have a SS relationship to start cement plastering when epoxy is tacky and other two FF relationships to make sure you do not schedule the end of plastering before epoxy is tacky nor after epoxy is dry.

Make sure your software can model this real life situation.

Best regards,
Rafael
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Thu, 2009-12-10 07:22
#13
Anoon Iimos
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Pandian,

Yes, practically concrete columns are easy.

for example:

1. you got rebars first
2. cover with formworks
3. place / pour concrete

All finish-to-start (FS)

Unlike suspended slabs, that you may do your formworks first, and there might be some overlapping of activities.

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Thu, 2009-12-10 07:19
#14
Mike Testro
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Hi Shanmagu

Absolutely correct.

Send an email to planning.services@xlninternet.co.uk and I will send you powerpoint demo that shows how it can be done very quickliy.

Best regards

Mike Testro
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Thu, 2009-12-10 07:14
#15
Shanmuga Pandian ...
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Hi mike ,
Thanks for your solution but let us take example ,
Columns Rebar - 10 days
Columns Formwork - 10 days
Columns concrete - 7 days

Here do you believe FS relation is correct ?

Regards ,
TN Shanmuga
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Thu, 2009-12-10 06:26
#16
Rafael Davila
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Creative FF Relationships

The 6th of January is 3 kings day, make sure the grass is green, you Eskimos! It is often viewed as the last day of the Christmas season, not at home; we have the “octavitas” another eight days of “parrranda” partying.

Parrandas is Christmas caroling Puerto Rican style. Friends gather late in the evening to go from one house to the next singing traditional songs. The parranderos must surprise the unsuspecting friends and wake them with their music. The home owner has already given plenty of "hints" that he is prepared to receive a parranda. The parranderos gather outside the front door and at a signal the musicians play and the rest sing. At each house they stop for a while and party (pitorro illegal rum and blood sausage is served), then they go to the next house. At each stop the owners of the house join the parranda and it grows in numbers during the evening. At 5am the last house must serve "asopao" rice and chicke stew.

Best regards,
Rafael
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Thu, 2009-12-10 04:29
#17
Mike Testro
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Hi Shanmuga

Here we go again.

Do not use FF SS links with or without lead lags - it is a lazy planners solution to a simple problem.

Only use FS links with no lags.

Best regards

Mike Testro
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Thu, 2009-12-10 04:43
#18
Vladimir Liberzon
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All dependencies shall be based on the real logic.
You can get the answer if you will explain the reason for selecting this link in the concrete case.
Best Regards,
Vladimir
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