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logic in premavera p3 (Urgent please )

11 replies [Last post]
Sun, 2005-05-29 04:50
Mohammed Foudeh
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Joined: 15 Apr 2005
Posts: 25
Groups: Petro-Chem / Oil & Gas
hello all:
i have (2) questions regarding the logic and sequencing in p3:

i will give an example to explain question (#1):
* the activity "block work" for ground floor starts after Steel Erection (its a steel structure building) and continue after the finish of mezzanine slab to complete the balance block there,my question is: what is the best method to link these activity, and to keep the logic true assume the block duration is 20 days and mezzaneins slab 5 days (no shutter to be removed because its( asteel sheeted suspended slab) ,the mezzaneine slab starts after steel erection with alag (20 days) and the steel erection starts after slab on grade with alag (5) days.

* The Second Question is:
in p3 you can link activities using the relation (Finish to Start with a minues Lag which equals to the relation start to start with same lag but positive ) my question is which relation is correct or the more correct in performing ascheduale to be submitted to a consultant (to match the american specification and to keep the logic ,float and longest path correct )?

thanks alot for all comments
Regards M.Foudeh
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Replies

Mon, 2005-05-30 10:34
#1
Mohammed Foudeh
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thank you farank ... my purpose for this plan is to be submitted to consultant ..i want to ask ,,is there any impact to the critical path if i used a finish-start with negative lag...

i will be thankfull if you have free time to chat using yahoo massenger ,because i have some questions in the construction planning,,,
thanks alot...and thanks for all comments
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Mon, 2005-05-30 07:43
#2
Frank Borcherdt
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Mohammed,

The answer to your query depends on what you hope to achieve from your plan.

If you want the plan to reflect how you intend to execute the works because you want the staff/contractors to follow the plan then you need to decide if you want the blockwork to commence at the 20% mark (and run out of slab after 1 day or assign a small crew so they never catch up with the slab) or delay until 4 days before the slab is complete and hit it with a full crew. You could also divide the area into 5 logical areas and do 1 day’s blockwork on completion of each area. There is no right answer but you need to make/get a decision.

If you are producing a plan to attempt to put things on the critical path to assist in substantiating delays then the longer blockwork activity will help bury the float.

I would try to break it into areas or segments/sectors you build a better model that will respond to issues that they arise e.g. if you have a unexpected condition occur that impacts only a small section of the slab and delays it the true impact of the delay is easier to assertain and removes the need for non FS relationships and lags.
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Mon, 2005-05-30 06:52
#3
Mohammed Foudeh
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the problem is when you want to linke two activites and you are not making adetailed scheduale you will be forced to make a finish -start relation with a negative lag in order to get the longest path correctly...and when you linking two activities with start-start relation with a + lag these activites will not be schedualed in the longest path...the other problem appears when you link 2 activites with different durations in a finish-start relation with anegative lag you will be forced to make the durations to be equale in order to locate the start date of the following activity ..for example
grade slab and block work (if we assumed that i can start block after grade slab ) and the duration of grade slab is 20 days and the block duration say 5 days if i want to link these activities i will say :
block work and grade slab are connected with a finish-start with a negative lag say 5 days ..now the block will start before the finish of the slab with 5 days and this is not accurate because in the actual i can start block after 20 % of grade slab starts because i allready have available slab to build block on it, to so;ve this problem i will start the block before the slab finish with say 20%(around 4 days from starting the slab or by another word finish-start with a ( -16) days lag and the block duration is 10 days i will face aproblem in the finishing of the block because it will finish before the slab finish and the correct logic is to finish the block after slab not before..and to slove this problem you will increase the duration of the the block to be the same of grade slab or less little pit,say 18 days to ensure the early finish of block after slab..you can do that but you will decrease the resources for the block to make it resonable..but when you submitt this logic to the consultant he will not accept because you increased the duration and that by sure will affect the total float of this activity ...so please what is the best method to solve this problem.....thanks all for your valuable comments
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Mon, 2005-05-30 03:53
#4
Jaco Stadler
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It May sound like not as easy but I have found it is always easier to show Milestones Example steel contractor to give access to Civil Contractor Etc.

This way it is easy.

But what is strange for me is that you are not using any props.
Also you dont say anything about Curing Time.

Cheers
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Mon, 2005-05-30 02:24
#5
DATTATREYA PADHARTHI
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Relationship should ideally be (FS) to obtain the best/accurate Critical path. But depending on the stage of the project/ details most of the times it is not possible to assign FS relationship & hence the uncertainity of SS/FF FS (with - lag) arise.
Simple eg is Piping Prefab & Erection. At Macro level (Levels 1,2,3) it is just not possible to have a FS relationship unless we go deep into the last possible activity.
The relation can be SS with some lag , FF with some lag (???). Not sure of the quantities/ methods etc)
We are not sure of the lags either.
SS/FF relationships (both) give a flexibility in defining relationships, but FS (with - lag) is again a deterministic which may not hold true while updating (you may require to change lag while updating)
This is better understood while using Pertmaster for risk analysis of schedules wherin lags are convereted into tasks.
In such cases it is better to have both SS & FF with lags for more accuracy in schedules.
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Mon, 2005-05-30 01:10
#6
Mohammed Foudeh
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hello all
thank you all for your valuable suggestions...please if any one could give me more deatails about this subject i will be thankfull .my mail is

(foudeh80@hotmail.com)
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Mon, 2005-05-30 00:18
#7
Raj Maurya
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First objective of linking the actvities, to show the proper dependencies in schedule, it is not for showing your negative and positive lags. For example you added SS relationship in two activity with some lag, this does not show how their completion are dependent. If you don’t want to show negative lag, try to break down the activity further.
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Sun, 2005-05-29 23:41
#8
Sunil Kumar
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Hellow Rolyn,

Is it true that all activities should have either a FS with a positive lag or a (SS and FF) for every activity OR it may affect the critical path.

Regards

Sunil
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Sun, 2005-05-29 19:44
#9
Alex Wong
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Sorry the display is not correctly posted
I will try again

MMMMMMMMMMMMMMMMMMMMMMMMMMMM
ss
BBBBBBB(1)--------------ff(+4)
-------BBBBBBBB(2)
------------BBBBBBBBBBBBBBBBBBBBBB(L)
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Sun, 2005-05-29 19:42
#10
Alex Wong
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I agree try to avoid using negative relationship
use SS to link the first area of mezz level slad finish and ff with the last block work

MMMMMMMMMMMMMMMMMMMMMMMMMMMM
ss
BBBBBBB(1) ff(+4)
BBBBBBBB(2)
BBBBBBBBBBBBBBBBBBBBBB(L)
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Sun, 2005-05-29 11:35
#11
Rolyn Jalea
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good day...
if there is no obstruction on the grade level, you can link the blockwork activity directly to the mezzanine level slab using FS relationship.
Use the combination of SS & FF relationship instead of FS with negative lag.
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