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What does "controlling" (instead of critical) path mean to you? (I will post my def. & use - based on IL IDOT work)

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John Reeves
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What does "controlling" (instead of critical) path mean to you?  (I will post my definition & use - based on IL IDOT work that is kind of useful)

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Rafael Davila
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Your costs are easy to purge no matter the software, just keep the billing costs if required, this is the concern to all including the Client. You have the right to keep for yourself confidential costs; they are relevant for your planning. Purging your costs makes it a Ghost Schedule. They happen very often, even if you do not realize it.

Rafael Davila
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Use a Ghost Schedule if you are worried client/representative might be intrusive and make sure you get it right in your Ghost Schedule.

Ghost Schedule

You might need a Ghost Schedule for many reasons. One such reason might be scheduling specifications that interfere with your ability to create a good model.

Terminal Float, the difference between planned completion and the completion date is mandatory under the NEC contracts. This risk allowance makes so much sense the NEC requires it but if the specifications require you to consume all available contract time they are denying you to plan with time-risk allowance.

Specifications that force you to split activities because of an artificial limit on activity durations, specifications that go as far as prohibiting the use of lag as well as many other valid ways to get a good model might be another reason for the need to create a Ghost Schedule.

For more details click the following Hyperlinks.

Contiguous Performance

No SS and no FF relationships allowed

Zoltan Palffy
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Vlad a lot of times the contractor doe snot want to committ to a certain number of men. Sometimes owners use it against them. 

I noticed that "real" resource and cost loaded schedules are rare.

Why?

Does it mean that the owners of busnesses are so dull that do not understand that proper planning prevents poor performance?

Why people do not even try to optimize project resource requirements and cost?

What do you think?

John Reeves
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There were a couple of answers so I answered this to my post.  I first wanted to clarfy that you are "coloring" days or weeks of an existing longer bar - so it is more like "controlling segments".  I greatly appreciate your input but we are talking apples and organges.  If you work for a road builder you have some 20 Mil jobs etc, but you also have some 500K=1 Mil jobs where resource loading is overkill.  "Everybody" wants a 1 or 2 page schedule with a key feature being that it is to spec and everyone can understand it.  I have worked at 22 companies in the AEC market for some of the largest companies and I am here to tell you getting "real" cost loading from contractors is like pulling teeth, "real" resource loading - even when in the spec - is rare and linear schedules are even more rare.  I am not saying that is a good thing.  I am talking about the largest companies, and when they do something like linear scheduling - they keep it internal because the mantra is "give them as little as possible, or we will have to it for every job."  I have worked at Airports and what-not where I have delved into these topics but there are a 1000 small little jobs that need a 1 or 2 page schedule for every 1 schedule using linear scheduling.  I am not against it and in the last 30 years things have changed where "now" most REs have gone to college and know more about scheduling than 30 years ago.  Didn't mean to preach, just was sharing a term that I do not see often.

Santosh Bhat
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John, this is exactly what linear scheduling is about, that only portions of a task may be on the critical/controlling path. The closest you get to doing it in CPM scheduling is through the use of SS/FF lags, and/or splitting activities into smaller and smaller discrete units. P6 is not the best tool for it (and neither is Tilos as as this backfits everything into a CPM schedule anyhow)

There's enough literature available if you wish to investigate it further, but here is a simple diagram that captures this:

1.gif (500×326) (ascelibrary.org)

 

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https://ascelibrary.org/cms/attachment/e7858e15-7d0d-46ee-970e-523901943dda/1.gif

Rafael Davila
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Not that I would, but you probably could.  It is you who claimed to showcase the methodology!

No matter if using P6, Microsoft Project, Spider Project or any other scheduling software if work can be done in parallel then the fault is on the scheduler.  Any experienced scheduler knows road construction can be done in many fronts at the same time, a good model will tell him what segments can be done in parallel or overlapped with others as long as there are enough resources.

Resource driven schedules are effective in neutralizing preferential logic, a well-known strategy by those who model resource constraints using software resource leveling rather than by forcing the schedule using unnecessary preferential logic.

You said “it was kinda cool” then showcase it.

John Reeves
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Controlling Path.  Lets take a small road building project, for those it might even still be acceptable to send in a schedule on a form filled in by hand.  Not that I would, but you probably could.  So you have a train of activity rough excav., sewer work, excavation and grading, pge stone, ca6 stone, etc.  Say it is a 2 mile long job, these activities overlap.  Say your bars are white.  You fill in with black a controlling schedule within those bars with the assumptions that only ONE activity can be "controlling" or most critical that day.  Why, well if it was done in P6 every activty on the entire project could be critical, and you mainly have at least 4-5 going at the same time - so you can claim anything is delayed.  In this method, only the "controlling" item can cause a delay.  It is kind of flawed, and I would still do it in P6 and create a target schedule that was non-overlapping to comply.  I thought it was kind of "flawed" and you could argue around it, but I learned to like it as way to simplify and convey sequencing within overlapping work.  I have never seen it used anywhere else, thought it was kinda cool.  You won't find it in the AACEi materials at all.  Nothing really to do with linear scheduling or producton rates although that could be part of it if you wanted to get fancy.

John Reeves
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Controlling Path.  Lets take a small road building project, for those it might even sill be acceptable to send in a schedule on a form filled in by hand.  Not that I would, but you probably could.  So you have a train of activity rough excav., sewer work, excavation and grading, pge stone, ca6 stone, etc.  Say it is a 2 mile long job, these activities overlap.  Say your bars are white.  You fill in with black a controlling schedule within those bars with the assumptions that only ONE activity can be "controlling" or most critical that day.  Why, well if it was done in P6 every activty on the entire project could be critical, and you mainly have at least 4-5 going at the same time - so you can claim anything is delayed.  In this method, only the "controlling" item can cause a delay.  It is kind of flawed, and I would still do it in P6 and create a target schedule that was non-overlapping to comply.  I thought it was kind of "flawed" and you could argue around it, but I learned to like it as way to simplify and convey sequencing within overlapping work.  I have never seen it used anywhere else, thought it was kinda cool.  You won't find it in the AACEi materials at all.  Nothing really to do with linear scheduling or producton rates although that could be part of it if you wanted to get fancy.

Zoltan Palffy
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to me it is the same as the critical path as both of these do control the project completion date.

its more like the critcal path CONTROLS the project.

Rafael Davila
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Dealing with production rates is not an advanced issue, it is basic and essential to good planning. LOB is all about production rates. 

Illinois Construction Scheduling Expert System I find it not good enough for management of construction jobs, no WBS, no cost accounts, no Earned Value, no resource leveling, no S curves, no seasonal production rate, no so many things.  But better than scheduling software that cannot show transparent production rates.

Press the full screen icon above for a better view   ↑↑↑

Activity assigned resources and their productivity usually changes when the crew composition/production-rate changes among the work shifts.  Not taking into account the work shifts and the resource skills availability, many with different production rates, is not real and will not make good planning models.

If time location charts are required and your software cannot draw them to your satisfaction then consider third party software that transfers the data using Excel, this is not a big deal.

Turbo Chart - Linear Project Software 

The following animation is only for the 3 activities of my sample Seasonal Resources Schedule, although they can be grouped, these charts get cluttered easily. Because of their summary nature too much information is missed.

To be useful the proposed methodology should be transparent to all stakeholders, site personnel included, and relatively easy while keeping all the functionality we expect of current scheduling software.

Santosh Bhat
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Perhaps  John is referring to a Department of Transport use, in which case it may be in reference to a linear schedule or linear scheduling?

I've seen "Controlling Path", "Controlling Activity Path" terms used in Linear Scheduling. Its akin to a critical path of a CPM schedule, but is derived from the location of tasks and rates of progress between tasks along the linear alignment of a project.  

There are also secondary controlling paths, etc, again analgous to "near critical paths" in CPM. 

I might this is quite an advanced use of Linear Scheduling, particularly if its a part of guidelines or recommendations of an owners authority! And if this is the case I am definitely interesred in finding out more about this!!

 

 

Rafael Davila
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AACE 29R-03 makes reference to a path calculation that breaks under any type of constraints, among others; traditional renewable resource constraints, consumable resource constraints, financial constraints, date constraints...  Longest Path is an archaic calculation valid for outdated CPM calculations when the models at the time (late 1950's) did not considered constraints or resource leveling.  If prospective path calculation breaks it is to be expectad that retrospective driving (controlling) path also breaks.

Ironically Line of Balance originated by the Goodyear Company in the early 1940's was already ahead of CPM with regard to dealing with resources and their production rates. Eighty years latter most scheduling software does not disclose resource production rates along with their unit of measure as if must be kept hidden very deep.

If using the software resource leveling/constraints most software longest path and float calculations will be unreliable.  P6 calculation of longest path breaks under resource constraints as documented by Oracle, P6 float calculations are unreliable as documented by many others.  Delay Analysis that is dependent on float/path calculation when it is so unreliable does not make sense.

Resource Driven Schedule

Anyway, John reference to IDOT tends to point toward road construction and Time Location Charts.

Tom Boyle
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AACE International terminology applies it to the apparent critical path when considering completed (in the past) activities.  E.g.  

CONTROLLING PATH - An alternate term used in place of 'as-built critical path' in order to technically preserve the use of the term critical path to denote only activity paths identified by float calculation using early and late dates....

Since total float doesn't exist for as-built activities, their membership on the Controlling Path is identified by other means (like retrospective driving path analysis.)

Rafael Davila
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Controlling Path and Resource Continuity

Controlling Path is the Resource Critical Path, in other words the critical path considering resource constraints.  Because traditional CPM technique did not considered resource constraints some use the term Resource Critical Path (RCP) to distinguish it from traditional CPM.  Resource-driven scheduling methods account directly for work continuity as well as re-source availability to ensure effective resource utilization.

A time-location chart (TLC) is a graphical representation of a construction program against axes of time and location (distance).

Line of Balance (LOB) Charts are just another graphical representation of the schedule, they show production rates as a slope. 

RCP software capable of modeling production rates such as Spider Project gives you the production rate values value within the Gantt table and can provide you with the Time Location Chart as well.  

Because Gantt can provide you with time production data distributed along the bars while showing you resource production data I see no need for the Line of Balance Chart.

Image-102 Click and zoom thumbnail for a better view.

In its infancy Line of Balance was a solely graphical tool, modern LOB software can find the Resource Critical Path but its use has been diminishing.  Most RCP & LOB software has not evolved enough to effectively deal with the resource continuity problem. 

The referenced paper suggests a convoluted way to identify "Controlling Path" in repetitive schedules.  While I agree that non graphical solution of complex problems is superior the proposed method is currently reliant on specific software and "macroprogram" where only the most significant resource will be considered (single resource) and this is not acceptable.  Maybe I am missing something but in this paper I only saw calculations for "Controlling Path" but nothing about reducing idle resource hours.

Traditional scheduling techniques (i.e., bar chart and networks) applied to repetitive projects have been criticized widely in the literature for their inability to maintain work continuity.  But resource continuity can be optimized if using Spider Project Schedule Optimization.

Schedule Optimization

Rafael Davila
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Maybe it is an outdated term for Resource Critical Path.

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