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SF link usage

22 replies [Last post]
Thu, 2009-09-10 00:21
Shah. HB
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Is there any place do we use SF relationship in the schedule? and how much importance is given to it?
so far i used for getting access for a specific activity not more about it
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Replies

Sat, 2009-09-12 05:43
#1
Vladimir Liberzon
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Relationships define restrictions that shall be used in schedule calculation.
They shall reflect or approximate the real work logic and constraints.
You can define schedule restrictions but the schedule shall be calculated basing on your restrictions.
Best Regards,
Vladimir
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Sat, 2009-09-12 05:22
#2
Anoon Iimos
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Hi Vlad,

I’m also not sure if I made the right question. Maybe, what I’m trying to find out is the right relationship(s) to use for a certain schedule, given a certain extent of details.

In other words, if there are no details, then there is no schedule, or there is no schedule to be defined.

And relationships (SS; FF; FS; SF or whatever), are only tools to define the schedule, or these are tools to calculate the schedule accurately?

best regards
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Sat, 2009-09-12 03:39
#3
Vladimir Liberzon
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Hi Anoon,
please specify your question, I am not sure that understood you correctly.
If you want to schedule only these three activities link them with both SS anf FF dependencies with 500 meters lag. Actually more because there is a need also for welding, joint control, coating and coating control before laying the pipes. And so there is a need to set the minimal distance between the crews involved in all these activities.
The schedule can be presented as the Gantt Chart and Linear Diagram (Time-Location Chart).
Of course it does not describe the project since there are also Block Valves, River and Road Crossings and many other activities.

Best Regards,
Vladimir
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Sat, 2009-09-12 02:22
#4
Anoon Iimos
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Excuse me Gentlemen,

I got a simple question for Pipeline Project.

For example: You got a 3-year contract for a pipeline, say around 500 KM (As a Construction - Contractor).

and Activities like: 1. Haul Road; 2. Trenching; and 3. Pipe laying (let’s forget details at the moment).

How do you present your schedule? I mean the first schedule or the Level 1 schedule. Are you going to elaborate relationships of the 3 activities mentioned above?

Thanks in advance.



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Fri, 2009-09-11 08:07
#5
Vladimir Liberzon
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Mike,
when we created this schedule it was done not only for setting the dates but mostly to determine what number and types of tractors, trucks, pipelayers, bulldozers, excavators, cranes, and other machines, what number of people of different skills to use in this project to be able to finish it on time taking into account risks and uncertainties.
Production rate is defined by the resources that are used. So there is not such thing as planned production rate. Some works can be done faster if to use more resources, or different resources, or two shifts, or three shifts. The task is to determine the optimal production rates, optimal crews, optimal number and types of resources that shall be used in this project.
I don’t understand what do you want to calculate in the spreadsheet and copy/paste. We do not calculate projects in the spreadsheets. Besides, to copy and paste into 250,000 activities is time consuming.

Best Regards,
Vladimir
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Fri, 2009-09-11 06:28
#6
Mike Testro
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Hi Vladimir

I have not had any hands on experience on such a large pipeline.

I would imagine however that the need for levelling would only apply to the work in progress and the next couple of stages.

1000 resources is a large number but not completely unmanageable - particularly if there are dedicated gangs allocated to each operation where one part of the gang is driving productivity.

For instance the trench excavation gang would most likely comprise the excavator - banksmen - linesmen etc and the production would be driven by the excavator output. I am assuming that surplus backfill will be removed later.

I would also expect gangs for pipelaying - welding - testing - backfilling. Each with its own driving resource.

If the planned production rate for any of these gangs is not being acheived - or is being exceeded - then some adjustment to the resources would be necessary.

This calculation would be done on a spreadsheet and copy / paste to the resource column until planned v actual productivity is close to parity.

How would a global resource levelling excercise improve on such a system.

Best regards

Mike Testro.
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Fri, 2009-09-11 05:51
#7
Vladimir Liberzon
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You did not answer if you have an experience of levelling 1000 resources in 250,000 activities project.
If you have done it manually it is especially interesting.
The best part of manual levelling is the continious nature of this work. Each time when you enter actuals (that are never as planned) you shall move activities manually again and again.
I expect that you enjoy manually moving 250,000 activities each week and playing what if scenarios trying to optimize the usage of your 1000 resources. Very entertaining!
When people talk about manual levelling it usually means that they don’t level resources at all.
Best Regards,
Vladimir
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Fri, 2009-09-11 03:51
#8
Mike Testro
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Hi Vladimir

I don’t know about Tilos but Graphisoft will balance resources.

A similar effect can be obtained in Powerproject using the task per line mode.

Powerproject v 10 has unlimited capacity for activities.

As I have said before I would never trust any software to balance resources.

Best regards

Mike Testro
Mike testro

Mike Testro
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Thu, 2009-09-10 17:27
#9
Rafael Davila
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Mike

I didn’t know Tilos can do Bar Charts, CPM Computations, Monte Carlo, Buffers and all the goodies we are used to without changing platform.

Yes this got to be good when you are building a road along with a few bridges and toll stations. So you use you linear reports for the road section, your Gantt charts for the bridges and toll stations and the CPM logic for your claims, all in one package.

After the features available in Spider Project I suppose Tilos got to do more than just the above. I am talking merely about every day tools commonly used in Construction Scheduling.

We all know it would be insane using dedicated software just for linear reports, very valuable indeed but not enough.

Just like Vladimir said a few days ago in other thread:

Discrete Activities: Discrete are best scheduled by other methods. Once the duration is determined by network analysis, it can be scheduled on the LSM diagram and coordinated with the linear activities.

Spider Project uses the power of computers to his advantage and keeps everything under the rigor of network analysis and then print the report when required.

For a further review on this simple technique follow the link:

http://homepages.cae.wisc.edu/~cee492/note/Sche12P_LinearSch_9901.ppt

It is an application so simple that over the internet for 20US$ (what 14 Euros) you can get all the functionality of Linear Scheduling without the network portion.

Best regards,
Rafael
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Thu, 2009-09-10 16:55
#10
Vladimir Liberzon
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OK Mike, it is very rough estimate.
Actually the section is 11 meters but 100m accuracy may be considered as sufficient. In this case you shall level the project consisting of 250,000 activities with more than 1000 resources.
I am sorry to say that Tilos and Graphisoft will not do this. So your proposal is not realistic.
Did you try Asta for such dimensions?
How long does it take?
Best Regards,
Vladimir
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Thu, 2009-09-10 16:26
#11
Mike Testro
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Hi Vladimir

I do recall our debate on the 1000km pipeline.

I do not remember what each chanage of distinct pipeline was required for the driving resource - probably welding and testing per 100m?

In which case there were probably about 10,000 sections.

If each section had 25 activities that would be 250,000 activites.

The linear method would require the sequence to start from one pumping station and end at the other.

Assuming there were sections between Pumping Stations say 1 station per 100 km then there would be 25,000 activities per stage.

If these were set up in Powerproject "task per line" mode then there would be 1000 lines per stage - each section linked FS along the chanage and creating a critical path per stage and totally.

Anyway the best software for linear projects is Tilos or Graphisoft.

Best regards

Mike Testro
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Thu, 2009-09-10 15:39
#12
Vladimir Liberzon
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Mike,
I already wrote that network logic shall reflect the reality as project computer model as a whole.
If real links are FS then fine, if anything else the software shall be able to model it.
You still did not estimate expected number of activities in the 1000 km pipeline construction model if to use only FS links. I can even specify my question - how many millions? I expect that analyzing this model may become very time consuming and resource levelling will take a long time.

Best Regards,
Vladimir
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Thu, 2009-09-10 15:30
#13
Rafael Davila
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Mike,

Tell me of just one major software vendor still using SF relationships as the only available option and not the PDM stuff as a proof you propose is the right thing.

Call ASTA and ask them to eliminate SS, SF and FF relationships and let us know when they will do it. I am sure Vladimir will love it to happen.

Best regards,
Rafael
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Thu, 2009-09-10 15:13
#14
Rafael Davila
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Vladimir

It got to be the same you used before. As with P3 Primavera stopped upgrading SureTrak long ago, they upgraded it to a 32 bit engine while P3 is still using a 16 bit engine. Well let see if we can still use P3 when Windows 7 is released and new computers start coming with the new operating system, even with the so called XP mode it might not. That if you can get a hold on a license.

If Spider Project uses other functions it does not matter as long as it does it correctly and the intreface is good, in agreement with standard CPM practice. I believe it does and also can do more than SureTrak, no shame this is what I use.

My point is that although these functionalities can be misused, like any, at times they are handy and should be available. I believe Asta and Power Project attitude toward providing the tools as per the client needs to be the right approach.

Best regards,
Rafael
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Thu, 2009-09-10 15:06
#15
Mike Testro
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Oh Dear

Or in the words of the immortal Walter Gabriel

Oh Dear Oh dear Oh Dear me luvlies.

If you restrict yourselves to only FS links then all your arcane problems will fade away like mist in Scotland.

Give it a try - what have you got to loose?

Best regards

Mike testro.
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Thu, 2009-09-10 14:23
#16
Vladimir Liberzon
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Rafael,
in any case all links that are commonly used in Network logic are of No Earlier Than type.
I did not play wuth Suretrak since early 90-s, so I assume that there are options that I don’t know about.
I am curious about Zero Total Float Constraint. I did not meet or notice it before. I expect that it is some special link, not usual SF.
Best Regards,
Vladimir
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Thu, 2009-09-10 14:12
#17
Rafael Davila
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Vladimir

In SureTrak we have a multitude of constraint options, each software is different, even P3 that belongs to Primavera but was developed by another team is different.

I modeled the issue using SF relationship with negative lag and Zero Total Float Constraint available in SureTrak, the activity was positioned where I wanted and showing no float even with the setting for showing open ends as non critical, with float. I have the software move it and the schedule remained true.

By the way I set my Gantt bars to display float. Immediately I noticed I was in need of some constraint to get my late dates and my float correct.

In SureTrak you create a hammock by designating an activity as a Hammock type; link its early activities to it as start to start predecessors and its later activities to it as finish to finish successors. Here FS is not allowed, SureTrak is a different league, maybe in the Minor Leagues in comparison to Spider Project, is not intended to be a Major Leaguer. But it is not a bad option for the Medium Sized Contractor.

Best regard,
Rafael
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Thu, 2009-09-10 13:47
#18
Vladimir Liberzon
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Rafael,
all PM software packages (except Spider Project of course) use only No earlier than logic constraints.
So if you will link Construction activity with Notice activity by SF relationship with negative lag (let it be 5 days) then Notice can finish five days before the start of Construction or later (imagine the notice that was sent one month later)!!! So it is not correct logic link.
In such cases we usually suggest to use FS from Notice to Construction but to set ALAP type to Notice activity.

Actually we do not recommend to use SF links at all. In most cases it shows some errors in Network logic.

The only reasonable usage is with hammocks like Project Management will finish when project result will be accepted.

Best Regards,
Vladimir
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Thu, 2009-09-10 10:45
#19
Rafael Davila
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Mike

Seems like some Primavera software do not allows you to use all type of links for Finish Milestones. SureTrak allows me to link Finish Milestones only with FS or FF relationships; I would not be surprised if P3 and P6 are different as I understand there are some conversion issues in P6 regarding Milestone dependencies.

Because these work in their own way maybe there are some programming requirements that justify this.

I do not recall using SF relationship within SureTrak as I never came across any of the few occasions where it might be used. Keep in mind scheduling software are not intended to exclude rare instances or to apply exclusively to a specific industry.

I can envision instances in which your contract requires you to give notice to the Owner a few days prior to the start of some construction activity. Here I would use SF relationship with your beloved negative lag. I have never used it in practice but it would take you less than 5 minutes to model this under any software.

I would schedule the notice task as an activity with duration of a few days to allow for time to verify on field, verify with subcontractors and others and to allow for a double check prior to sending the notice. This requires the relationship to be tied to the end of the activity.

For another example follow showing the use of SF relationship with a negative lag in preference of FS just follow the link:

http://www.htcprojectcontrols.com/TTB2004-2.pdf

Best regards,
Rafael
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Thu, 2009-09-10 08:56
#20
Mike Testro
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Hi Ronald

Insofar as milestones have zero duration the finish start points are simultaneous and are therefore completely interchangeable.

The FS SS FF SF demoninations are therefore meaningless.

Best regards

Mike Testro
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Thu, 2009-09-10 08:40
#21
Ronald Winter
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Even though most CPM software packages will let you break this ‘rule’; the only correct relationship link from a start milestone to a finish milestone is a Start-to-Finish relationship type.
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Thu, 2009-09-10 04:09
#22
Mike Testro
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Hi Shahul

With a SF link you will be building the thing backwards.

Best regards

Mike Testro
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