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Lag of Relationship

36 replies [Last post]
Izam Zakaria
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Guys,

Is it possible if we put negative integer for the lag relationship? I guess it doesn’t make sense because it can’t drive the activity…. Am I right?

Replies

Good software shall be flexible enough to simulate any situation in your projects. It does not mean that all software capabilities shall be used in every project. If the software cannot do something it becomes planner’s restriction.

Izam Zakaria
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Trevor Rabey,

Whether software allow it or not, it just only tools.The most important things how we manage the sequence and links. Have u notice some of relationship type and lag in P3 is not recommended in P6? then they have reason why they continous update the the planning software version.In a nutshell we can’t simply rely on software....
Mike Testro
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Hi Trevor

There was no entry for "jhuggiuhu" in google but there is a couple of hits for "jhuggi uhu" I think you may have misspelt it.

Best regards

Mike Testro

Trevor Rabey
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Mike, MSP allows edays as lag.
Trevor Rabey
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Denni, just because software allows it, doesn’t mean that it is a good idea or that it is compulsory to use it, or that it should be splashed around at random.
There may be some special cases where it might be useful, but smack bang in the middle of a critical path network isn’t one of them. Careful judgement, which links to use where, and which not to use, makes the difference between good modeling and bad modeling, and you get to choose which you prefer. There are other things that software allows that should not be used except in very special cases maybe, if at all. MSP allows scheduling backwards from a finish. Someone must have asked for it, it might be useful in some cases, but is definitely nothing to do with the critical path method. MSP also allows date constraints. It even lets you type in "jhuggiuhu" as a task name but not a good idea.
Trevor Rabey
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Denni, just because software allows it, doesn’t mean that it is a good idea or that it is compulsory to use it, or that it should be splashed around at random.
There may be some special cases where it might be useful, but smack bang in the middle of a critical path network isn’t one of them. Careful judgement, which links to use where, and which not to use, makes the difference between good modeling and bad modeling, and you get to choose which you prefer. There are other things that software allows that should not be used except in very special cases maybe, if at all. MSP allows scheduling backwards from a finish. Someone must have asked for it, it might be useful in some cases, but is definitely nothing to do with the critical path method. MSP also allows date constraints. It even lets you type in "jhuggiuhu" as a task name but not a good idea.
Mike Testro
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Hi Denni

The only possible use for a FS+d lead lag is to allow for curing or drying out time.

The problem is that the extended link takes on the calendar of the preceding activity when curing and drying out takes place on a 24/7 calendar.

In powerProject you can set the start link to +?ed - ie calendar days but if the link ends mid holiday the critical path is removed upstream.

I used to set up a specific task between - say - laying a screed > laying stone flooring of 1 day per mm of screed - called "screed drying" and this is set to a 24/7 calendar.

This also broke the critical path.

I now set up a "buffer" using two milestones:

1. Linked to the end of screed
2. Linked to end of the lead lag link and linked to laying stone floor.

These are summarised into a bar called "drying out period" using the regular calendar and the critical path is maintained across holidays.

The PowerProject buffer task option is no use as it tends to go critical even if there is float all around it.

Best regards

Mike T.
Denni Effanusandhi
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This neg lag is available option on any planning software.
We can use it as long as we have acceptable reason.

Whats Ur opinion about positive lag such as FS+d?
What is your reason to use it, or you never use it at all.

Cheers
Mike Testro
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Thank you Vladimir

That was the 1st real laugh of the day.

Being an arrogant Englishman I have no interest in other languages - thoug I am fluent in Rubbish.

Best regards

Mike Testro.
Mike,
sorry for my poor English.
I meant ship body.
Vladimir
Mike Testro
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Hi All

Please tell me what is a ships corpse?

Best regards

Mike Testro
Hi Patricia,
I’ll be glad to answer if you or your collegues will have future questions.
Best Regards,
Vladimir
Hi Mike,
we did not discuss not only calendars but also Resource Critical Path. With limited resources traditional Critical Path method does not work.
We did not discuss simulation of working in shifts, creating and managing buffers and many other interesting topics.
So we have good themes for future discussions.
But consider using both SS and FF links with lags between two activities - it is a good replacement for FS links in certain cases. I hope that Powerproject supports multiple links between activities.
By the way Caspian project used 10 different work weeks.
Today we are involved in the development of Russian Pacific Area program. It is very close to Sakhalin Island.
Best Regards,
Vladimir
Patricia Le Clainche
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Thanks Vladimir.

I do not have such experience, with such detailed schedules and so many tasks. That is interesting... I am going to think of giving a lesson to a few project managers I know.
Best regards.
Patricia







Mike Testro
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Hi All

Please calm down dears - its only a thread.

But then again I am delighted that the discussion is going so well.

I think that the contributors are begining to understand that unles there is a fully developed FS linkage showing a true critical path - with a real resource modelled input (we have not discussed this bit yet) - then there is no real control of progress in relation to events that may combine to delay progress.

Wait until we talk about calendars - that is another overlay.

I worked on a project on Sakhalin Island (calm down Vladimir - I stayed in UK) - where there was 8 different calendars for different daylight hours.

There are many other factors to consider before a project has been properly planned.

Watch this space.

Best regards

Mike Testro.
Hi Patricia,
Caspian Pipeline construction schedule used 1145 renewable resource types (people and machines) and only 28 materials (we selected only main materials), ship corpse construction schedule used 66 renewable and 64 consumable resource types.
Resources were assigned in the fragments, so adding fragments we added corresponding resources.
So we had the schedules for each resource of the project.
One of the scheduling tasks was to determine the necessary number of people and machines that shall be used to finish the project for the certain date.
Best Regards,
Vladimir
Patricia Le Clainche
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Hello Vladimir,

And how do you manage resources for such schedules ?

Best regards.
Hi Trevor,
the schedule we created for building the corpse of one ship consisted of more than 11000 activities. It was fun because the number of typical fragments was small and the schedule was created in two weeks.
Next ship corpse construction schedule was created in one day because we already had all necessary fragments.
You are right, large schedules are not created by entering each activity data one by one.
Best Regards,
Vladimir
Hi Mike,
imagine the situation when for some reason the following task is executed faster than the preceding one. It will start with 500m lag (FS relationship that you suggested) but then the distance will become 400 meters, 300 meters and then the work will stop waiting until 500 m section will be done on the preceding activity. Then this race will repeat.
Besides the lengths of sections between different crossings or soil changes are different. Sometimes it is 800 meters, sometimes 1300.

Creating such schedules we use different approach.
Project Planner creates the schedules for typical schedule fragments like construction of 1000 meters of pipeline in certain type of soil. The project schedule is created by inserting these fragments using multiplication factor that reflects the actual volume (quantity) of work to be done (length in this particular case) in the real schedule at the certain places.
If you have ready to use typical fragments library you will be able to create any pipeline construction schedule easily and fast.
The same approach is used for creating any large schedules where the types of work are repeated.
Mike Testro
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Hi Trevor.

Much thanks.

Best regards

Mike Testro
Trevor Rabey
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I see you are holding the fort all by yourself over here.
I agree. If a project has 20000 Tasks then that’s how many Tasks have to be modeled. Whatever the software, there is fast ways to do the editing and data input, and there are also slow ways. But 20000 Tasks or so is a piece of cake and very fast to set up, if you know how to use concatenation and a few text editing tricks (batch replace etc). And if you don’t then you resort to insufficient detail glued together with weird links and negative lag.
Mike Testro
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Hi Vladimir

Just for the pipeline:

You are working in 500m sections and the key relationships are:

1. Dig Ditch
2. Install welded and tested Pipe
3. Connect to previous pipe
4. Backfill trench

My calculations are that 500m sections over 750km = 1500 sections + 9 activites for each section = 13500 tasks

15 min for each 11m pipe = 11.5 hours for each 500m section.

In PowerProject it would take me less than a day to set up a FS linked programme for the full 750 km line.

Of course river crossing and block valves would then have to be bolted on to the relevant section along the chainage.

Does your spider software allow:

1. Copy paste between columns and spreadsheets.
2. Filter on trades into 1 view
3. Global FS link between filtered trades

If so you can do it in the same time.

Also if your spreadsheet allows for concatination of text then you do not have to type in every 500m chainage in your barchart.

I hope all that makes sense.

Best regards

Mike Testro
The distance between different types of work is 500m. The sequence: Transportation, ditching, welding, Joint control, Joint insulation, joint coating control, testing, lowering, backfilling. Of course there are many other types of work like road and river crossings, Block Valves, etc.
Best Regards,
Vladimir
Mike Testro
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Hi Vladimir

How many m of ditching is done before you lay the pipes in the trench?

When do you backfill and reinstate?

Is Welding - Control - Coating done prior to laying the pipe or after it is in the trench?

Let me know and I will try to set up a reasonable FS model.

Best regards

Mike Testro

Nestor Principe
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Hi Mike..

Am starting to like your style. ha-ha-ha..

Cheers..
Hi Mike,
the average speed per day is 500 meters.
One section is 11 meters.
So each activity (welding, ditching, control, coating, laying, etc.) will last 15 minutes if to follow your advice. The total pipeline length is around 750 km.
Just imagine the dimension of the model.
Our model of this construction consisted of 9000 activities.
I don’t see the real advantage of this approach if to compare with combination of SS and FF links with volume delay.
Best Regards,
Vladimir
Mike Testro
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Hi Nestor

Now you are just being silly.

The programme would be in much greater detail than the drawings.

Best regards

Mike Testro
Mike Testro
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Hi Vladimir

You cite activities working in parrallel when it is really sections.

You do a section of ditch then lay a section of pipe along the chainage.

You have to break down the pipeline into sections - daily if necessary - certainly no more than 10 days - and use FS links between each section.

Once you have a cascade for each section it is very easy to copy paste and link up FS sections.

You then have a true critical path for the pipeline.

If your ditching gang hits an obstruction in section 17 you can then show the likely delay effect immediately.

Best regards

Mike Testro
Nestor Principe
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Good Day Mike..

That was incredible. I can imagine the person whose doing the construction need not even to look at the drawings because all the details are already in the schedule.


Cheers..
Mike,
the scheduling model shall represent the real life. So if some activities can be done in parallel then SS and FF links shall be applied.
Simple example from the pipeline construction project:
Ditching, Welding, Joint Control, Joint Coating, ... can be done in parallel with the positive volume lags.
I am against negative lags but positive lags are sometimes necessary.
Of course it is necessary to use both SS and FF relationships linking two parallel activities.
I prefer to use Spider Project, but also think that it does not depend on the tool.

I agree with all other rules that you suggested.
Mike Testro
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Hi Patricia

How many activities do you have in a single project?

The answer is how many do you need.

Please follow my basic rules - I say my rules because most memebers of PP threads say I am wrong - you choose.

1. One activity represents one trade in one location with no interuption.
2. If an activity is more than 10 working days it is too long.
3. Only use Finish Start links.
4. Every activity must have at least one outgoing link - if only out to project completion.
Never Use:
1. Lead lag links
2. FF SS links.
3. Constraint flags.

This applies to whatever software you are using.

I prefer PowerProject but even in P6 or 5 the same bottom up planning rules apply.

I have just completed a programme for a 3 storey house with more than 2500 activities - it was the minimum necessary.

Actually if you have a copy paste facility in your software it can be done very quickly - 16 hrs in the last case.

Thanks for listening and best regards

Mike Testro
Patricia Le Clainche
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Hello everybody.

I share Mike & Trevor’s opinion.

But I just have one question : how many activities do you have in a single project (for instance planned through Primavera P5 ou P6) ? If you have to split a task in several, what is the duration of each of them ? I knew some planners who chose to use lags in order to avoid having too many tasks, too much detailed to manage in a single project.

What do you think about it ?
Kindest regards.
Patricia
Mike Testro
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Hi All

Trevor is right - use of any lead lags whether positive or negative are a bad thing - they distort the critical path and the logic goes haywire when entering part progess that bridges the link.

Stop doing it now.

Break up the activities into constituant parts and use FS links for each activity.

In PowerProject this takes seconds but I understand that with all P3 users this is a labour of love that may take hours.

Best regards

Mike Testro
Denni Effanusandhi
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Depends on the task.
1. If we have 1 piece of pipe to be CUT fs BEVEL fs FITUP fs WELD, so the relationship should be FS without neg lag.

2. If we have 1000’s piece of pipe and only have Activity ID for CUT fs BEVEL fs FITUP fs WELD with limited time and resource, we may apply those FS negative lag.

3. Lets say we prepare level 1 of EPCI project schedule which contains only Key Milestones, Engineering, Proc, Fabrication & Installation. The Fabrication may be started when engineering has finished by 70%. In this case we can use FS-30% of total Duration of Engineering to start our Fabrication.

The best approach is to apply the combination of SS+d and FF+d to avoid “Out of Sequence” issue.
Trevor Rabey
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Negative lag is a very bad idea because the trigger for the start of the successor goes off in the future.
"Task B cannot start until 5 days before Task A has finished"
You cannot know when to start Task B because you can never know if you really are 5 days away from the finish of Task A.
You really mean that a certain part of Task A must be finished before Task B can start, so you must identify that part.
Good modeling, rather than lazy modeling, simply requires that you break Task A into two parts, A1 and A2, so that you can make a FS link from A1 to B and also from A1 to A2.
Lloyd Young
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Yes it is possible to put a negative lag on the relationship. In some cases you may have a Finish to Start relationship with negative lag to allow the activity to commence prior to the pred finishing, although in the real world this isn’t a "Finish to Start" logic but it may occur when, the activity has procurement built into it and materials are ordered ready for the work to commence as soon as the pred is finished.... as an example. Note this still can be part of the critical path so yes it can drive, obviously depends on the negative integer you use.