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EFFECT OF CONSTRAINTS IN SCHEDULES

16 replies [Last post]
Mon, 2009-03-23 16:10
Kumar I
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IN CONSTRUCTION PROJECTS,IF THERE ARE NO ACTUAL CONSTRAINTS IN THE CONSTRUCTION PROCESS.IF THE CONTRACTOR INDICATES EARLY CONSTRAINTS TO INDICATE THE AVAILABILITY OF CERTAIN EQUIPMENT OR MATERIAL TO COMMENCE CERTAIN ACTIVITIES,IS THE BASELINES WHICH SUCH SCHEDULES ACCEPTABLE.WHAT EFFECT THESE CONSTRAINTS HAVE ON THE SCHEDULE CALCULATIONS.

IF MATERIAL PROCUREMENT ACTIVITES ARE NOT INCLUDED IN THE SCHEDULE,IS IT ACCEPTABLE TO INDICATE RELATED CONSTRUCTION ACTIVITIES WITH CONSTRAINTS RELATED TO MATERIAL DELIVERY
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Replies

Wed, 2009-03-25 13:24
#1
Mike Testro
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Hi Bo

We are Ad Idem on this subject.

I am - as always - in awe of the range of English vocabulary used by people who have had to learn it as a second tongue.

I claim fluency in two languages - English and Rubbish.

I look forward to swapping views on other threads.

Best regards

Mike Testro
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Wed, 2009-03-25 11:19
#2
Bo Johnsen
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Hi Mike,

I do not mean “trick the programme" as to produce a result artificially, but more to “trick the programme" to simulate the real situations taking place on a construction site with respect to the Contract, the BoQ, the specifications, the drawings, etc. If one wanted to produce artificial results, hard constraints would be the easiest way out and that would certainly contradict what I’m always trying to get in programmes, being the highest degree of flexibility.

In my opinion programmes always have to be true to the nature of the work for a specific construction project and able to show what the most likely impacts will be if delay events occur, no matter if caused by the Contractor, the Client, both (concurrent) or Third Party. Therefore, I normally treat the “Total Finish Float”-values as one of the most important issues of all in a programme and check these values for their reasonableness (is that an English word?) before submitting the programme both externally and internally.

However, in many situations all the planning software systems out there on the market do not contain the features necessary to simulate the most likely impacts correctly in relation to Client’s deliverables, approvals, handing over, possession of site, sectional completion, taking over (partly or fully), intermediate milestones, etc. Because of this lack of features one has to “trick the programme” by utilizing e.g. some of the options mentioned in misc. posts below. Take for example your own experience with Powerproject: “…buffer task is not practical as…” and “…hammock task is better…”. Yes, one is better than the other, but is it correct? Therefore, I would also call the use of a hammock task for “trick the programme” - no offence - because one have to use what is available in the software when the correct option is not.

And as an offspring (and maybe another forum): If using a hammock task named “Contractor’s Time Contingency” how many contract forms (or arbitrations) accept this? NEC maybe, but what about JCT, ICE, ICC, FIDIC, etc.?

Best regards

Bo
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Wed, 2009-03-25 07:32
#3
Gary Whitehead
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You don’t know my client!

Thanks for the welcome -I actually joined a couple of years back, but lost my login details
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Wed, 2009-03-25 06:36
#4
Mike Testro
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Hi Gary

If you assume that no progress ahs been made then the solid bar will start to generate delays in week one.

Probably not a bad idea as it will prompt the client to defend his postion and give accurate progress reports.

By the way - welcome to PP - I have just noticed that you joined up this month.

We look forward to your continuing contribution.

Best regards

Mike Testro
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Wed, 2009-03-25 06:26
#5
Gary Whitehead
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Thanks Bo & Mike for your comments. I can see the value in using a bar to help highlight to the client his responsibilities and impact on the plan.
I’m still uncomfortable though in reporting progress that is ’presumed’ rather than verified. I’ve always worked on the principal that unless I know what progress has been made, then no progress has been made.

It’s probably just me following an idealistic principal vs. what is more practically useful.
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Wed, 2009-03-25 06:16
#6
Mike Testro
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Hi Bo

I do not think it is good practice to "trick" the programme to produce a result artificially.

I make it a point to avoid all artifical restraints with two exceptions.

1. Lead Lags for curing - drying out perios but set to calendar days. (A lead lag will take on the calendar of the predecessor unless over written)
2. ALAP postioning in design - procurement sub charts.

Any other situation can be dealt with using solid bars and FS links.

Powerproject does have a "force critical" option to apply to bars but I have not yet forun any use for it.

I have discovered that using a buffer task - as I did in my worked example - is not practical as all up stream tasks leading to the buffer show critical - a by product of a buffer which has zero duration.

A hammock task does it better.

Best regards

Mike Testro
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Wed, 2009-03-25 05:52
#7
Bo Johnsen
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Hi Gary,

If you can represent the Client’s activities with a solid bar instead of milestone - which is not always possible - it would always be best to avoid the "hard" constaints such as MSO, MFO, SNET, FNET, etc. as they will distort the picture of your programme when being impacted by misc. events.

Maybe you can also view it as an advantage instead as a "downside" that you can give progress on the Client’s deliverables as you then every month in the Monthly Progress Report can graphically show that you "presume" he is on track - which is the only thing you can do if haven’t been informed otherwise. You do not "claim progress", but "presume progress". And as you say it will definitely be on the CP - and he is reminded every month by the assumed progress bar instead of just having a milestone which basically says nothing in relation to progress.

Going back to Kumar’s question I sometimes use "soft" constraints if the software I use have this feature. E.g. in MS Project you have "Deadlines" which will show criticality for a milestone, if applied, but won’t affect scheduling. In Pertmaster there is a feature where you can tick off "Always critical" for an activity and in some ways that is a bit smarter because it doesn’t relates to a specific date which "hard" constraints or "Deadlines" do, but is just always critical. Not knowing Powerproject that much, but having played with a trial version it has something similar called "buffer tasks" (presented in Mike’s Bottom-up programme example from another thread).

Sometimes I also apply a FS-link with a big lag from an intermediate milestone to the completion date to make that intermediate milestone critical if not going down the road with an activity/bar named "Contractor’s Time Contingency" / "Terminal Float" as other people have described.

So there are ways out, but I have to say that I’m not sure which one is correct or best to use and most of the times I feel I have to "trick" the programme. Maybe somebody can explain the most appropiate option to utilize dependant of the situation?

Regards,

Bo
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Wed, 2009-03-25 05:51
#8
Mike Testro
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Hi Gary

The programme is to be used for managing the project showing who is responsible for the timely delivery of what.

The value of a solid bar is that it is up front and visible.

The client cannot ignore it.

If you are not getting progress reports from the client - which you should - then put in assumed progress on a time percentage basis.

This will deffinitely sharpen the clients attention at progress meetings when you say the programme shows 80% completion and the delivery which is due in 2 weeks time - after that your claim for EOT will be rolling in on a weekly basis until delivery is achieved.


Best regards

Mike Testro
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Wed, 2009-03-25 05:03
#9
Gary Whitehead
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Oh, it’ll definitely be on the cp!

What’s the value of a solid bar over a constrained milestones? The downside as i see it is that
a) I would be telling the client his progress on his deliverables, when it should be the toher way round.
b) I’m not going to get an update from the client on, say, land easements every 2 weeks. So for my fortnightly schedule update, I’ll be forced to either claim progress with no evidence to support it, or show slippage which probably isn’t really happening.
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Tue, 2009-03-24 12:06
#10
Mike Testro
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Hi Gary

I would put in a solid bar activity to represent the unknown external activity.

I would give a bright recognisable colour code and if possible make sure it is on the critical path.

Best regards

Mike Testro
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Tue, 2009-03-24 11:55
#11
Gary Whitehead
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I have only ever used start & finish constraints for external activitites over which the project team have no control -typically client deliverables or government approvals.*

Mike’s post would suggest this is not an appropriate use of them, but I’m interested to find out why not, and what alternatives other esteemed planners use to represent external (but potentially critical) activties?

*Of course, I’ve also used them for those 5-min notice jobs where management require a pretty picture to take to a meeting. But that’s not planning, that’s making pretty pictures.
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Tue, 2009-03-24 09:50
#12
Stephen Devaux
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Hi, Kumar. I agree with Mike re the ALAP schedule, with one minor amendment: if you are using earned value metrics and reporting, the EV baseline (BCWS, PV) for *schedule metrics only* should be on the ALAP schedule.

In that way, anything that is delayed from the baseline represents an EV package whose late accomplishment will delay the project completion. If the ASAP (as soon as possible) baseline is used for schedule, EV packages which may be off the CP with lots of float will nevertheless show up as being late on your schedule variance and schedule performance index.

Fraternally in PM,

Steve D.
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Tue, 2009-03-24 04:13
#13
Mike Testro
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Hi Kumar

ALAP means As Late As Possible.

it is a type of constraint that sets the task at the end of available float and becomes critical by default.

Use of this type of constraint should be limited to the procurement sub chart that I described.

It is not good practice to use it in the main programme as the logic and criticality is distorted.

Best regards

Mike Testro
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Tue, 2009-03-24 01:56
#14
Safak Vural
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Dear Kumar,

When you are preparing the baseline create an activity for these material procurements. At least you will have the ETA dates. Call these activites procurements and FS link with the Project start milestone. Give durations as the activities ends in the ETA dates. So you can FS to your activities (You can also emphasize CLIENT deliverables also). At weekly progress updates you can "Update Progress" for this activities unless you have an alternative ETA dates for the deliverables. If you have he alternative dates you can write the ramining dates from data date to this procurement activities. It will not effect any earned value analysis or another reports because it will not have any resources (That means you can have less % from previous week)

This is better thatn using constraints in 2 ways,
1- Check abominations topic
2- Emphasize on deliverables

Regards,

Safak
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Tue, 2009-03-24 01:05
#15
Kumar I
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Thanks Mr Mike,
Can you please clarify regarding ALAP constraints
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Mon, 2009-03-23 17:36
#16
Mike Testro
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Hi Kumar

First thing - please do not use capital letters in threads - it sounds as if you are shouting.

Start finish constraints should not be used in a critical path programme because they distort the logic.

It is good practice to put in an activity that represents delivery and availability of certain equipment linked to the relevant activity.

Particularly if the equipment is Employer supply.

Better still to set up a sub-programme of the procurement stages and link it to the first activity that requires the material - using ALAP constraints.

If there are a number of activities that need the procurement input then set up a hammock with the activities and link the procurement to the start of the hammock.

In Powerproject you have to put a summary bar over the hammock to create the link.

Anyway - AVOID USING CONSTRAINTS!!!

Thats me shouting.

Best Regards

Mike Testro
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