"it is called Resource Critical Path or Critical Chain"

when you define resources as: Materials, Equipment, & Manpower, these items will compose your physical activity(s).

which means that a certain physical activity is a composition of several elements that can become critical in anyway!

may it be in time, (when calculated in terms of float / CPM), or maybe in quantity or design and function

for me, value is important and must be calculated as to represent the expected end result that the customer wants.

The guy who started this was looking for an answer about the percentage of sactivities that should be on the critical path.
Since then we have had all sorts of assumptions and ideas
For me assuming the critical path is determined as per P3 ie less than say 5 days float there may be no critical path.
In the alternative all activities may be critical if for example it involves the collection of rainwater in a desert with an end date related to an amount neccessary to be collected.
I like to draw up a programme and then press the calculate button
Normally I will have an idea where I expect the path to be however sometimess its not there because
1. I have a mistake in the logic (this occurs often)
2. I have time/date constraints that shove the path in a different direction
3. I have resource constraints

However for me there is no hard and fast rule about the % or the path I follow the rule that if it isnt what I expected to be why has that happened

Personally i feel whether the roof goes on first will depend whether you are building an aircraft hanger or a house

Annon,

No offence just for your info, on my experience I have done so many times a top down constructions which roof & trusses first before the walls. I hung it due to weather condition so the workers can still work during rainy days and the projects are all successful. (I know that the logic is the main discussion in here and not the physical activities.)

Regards,
Rodel

Steve,
I also pretty much agree with your posts though we use slightly different techniques.
I will answer your questions and hope that it will clarify unclear items.

1) "It’s not clear to me why uncertainty/variability on resource availability is any different from uncertainty/variability on an activity."

Let’s suppose that some material is supplied weekly. The quantities are known and requirements on each activity are also known - no uncertainty at all! The only uncertainty is the precedence, it is not obvious what supply activity shall precede to what consumption activity. It is not clear when and on what activity supplied material will be used. It depends on the project schedule that shall be calculated taking into account supply constraints.

2) I did not object to calculating CPM schedule for project analysis and resource optimization. But real feasible floats in the working schedule shall be calculated taking into account all project constraints. We also recommend to use NPV as project success criterion (http://www.spiderproject.ru/library/mps.ppt) but I don’t agree that adding resources is an easy task. If you can install only one crane in the construction site you shall calculate project schedule with this restriction. It is physical.

I will look at your paper later, I think that we use similar approaches.

Best Regards,
Vladimir

Vladimir,

As usual, I pretty much agree with everything you say -- but I feel some of these ideas are so fundamental that it is important to go deeper and discuss the implications.

First:
"4) The steel may be purchased for not one but for many activities and many times during project execution. In this case simple approach with creating link from delivery activity to consumption activity does not work. It may be impossible to know which delivery provides materials that will be used on each activity."

It’s not clear to me why uncertainty/variability on resource availability is any different from uncertainty/variability on an activity. I can think of many project situations (Which of several chemical compounds or delivery devices will prove best for a specific pharmaceutical market niche? Which platform we’re testing will be best for this system? Which precise drilling hole, and how deep, will result in an oil well?), where there is great uncertainty that will affect the start of successor activities.

Second:
"When resources are limited then classical approaches to calculating activity floats based on network logic do not work."

This does not obviate the need to generate an optimized schedule based on network logic, though. In fact, even though I suspect we are in complete agreement that a schedule that is not resource loaded and adjusted for resource unavailability must not be considered the "working" schedule (in other words, it should be the resource-limited schedule, and the working critical path should be the Resource Schedule longest path), this makes it even more important that an optimized CPM schedule be generated first:

a. An optimized schedule can often "pull" an activity’s dates to a resource’s early "window of availability" and thus avoid what would otherwise be huge delays due to later unavailability. This is especially relevant, in my experience, in multiproject organizations and with equipment resources like clean rooms, testing ranges, etc., where availability windows open and close according to the needs of other projects.

b. In the Total Project Control approach, it is absolutely crucial to identify and quantify the constraints and their effects on schedule and project profit. The optimized "classical" CPM schedule is what I’ve started calling the "Newtonian" schedule, i.e., as much as possible, the only limiting factor should be the laws of physics: you can’t proofread something till you’ve written it; you can’t put on the roof till you’ve built the walls. (If you can figure out a way around such physical laws, then see if doing it that way will increase project profit without unacceptable risk -- if it can, do it!)

c. When going from the optimized CPM schedule to the resource schedule, the delays will be due to (primarily resource) constraints. These can now be measured. In TPC, the reduction in project profit due to each constraint is called the Cost of Leveling with Unresolved Bottlenecks. And that’s the CLUB you use to spend the extra $20,000 to get the resource you need to bring in the delivery by three weeks at $50,000 in increased project profit per week. And the key is: it’s (usually?) a lot easier to change resource availability than to change the laws of physics!

d. In a continuing and multiprojected organization, it is crucial to collect data about CLUBs, by both individual resource/skill and department. The CLUB is of great value to functional managers in their neverending quest to justify staffing up to sate the needs of the projects they support. These CLUB data should be a key part of the output of the project postmortem and ABCP analysis. Failure to do this is one of the main reasons that the same resource’s unavailability delays project after project month after month and year after year, with no improvement because everyone "works around" such delays by planning activities that could be done in one day for one week, because they know the resource could take that long to become available!

For more on that, you can check out the "Post Mortem Agenda" document among the resources at:

http://www.totalprojectcontrol.com/resources/resources.html

Thanks for the info, well i think it really depends on how we will link correctly our activities which will also come from a good knowledge of what we are doing specially familiarization...

Cheers,

Joseph

Can we be simplistic and answer the following yes or no?
1. The critical path must be the longest path from start to completion.

2. The only way activities on this path have float is because certain activies are constrained?

3. Constraints are really activities not defined on the network, (Because they may be by others outside the contractors control.) activities up to starting a steel frame are non critical because steel start is constrained by a steel delivery milestone (steel has been procured by client to a set delivery date.). All following activities are critical. The delivery milestone has behind it a series of critical activities not defined in the programme.

4. If an activity "steelwork procurement by others" had been included in the nework (from contract award to steel delivery (F-S) Then that activity would be on the critical path, and all activities on the longest path would be critical.

Hope that makes sense, from a simple building planner.

Hi all
I think that the critical path is as good as the logic used in the schedule. It depends also on the various calendars pertaining to the critical activities. All of these combined with your own definition of the critical path envelope i.e. total float =< x days may provide a less than accurate depiction of what is going to define your completion of the project. Ultimately, the schedule, particularly the critical path will reflect the thinking and experience of the project team.
I agree with what Ron Winter has to say in regards of the longest path being a more accurate tool to identify which are the activities that really drive your completion date. In fact, I go one step further. When reviewing the critical path envelope, I look at the logic driving the longest path(s) and encourage for those (and only those)critical activities to be broken down to a point where the only relationships used on the such path are FS. This practice is important when setting up the baseline. Obviously, the limitations to the above are 1) the amount of information available when building the schedule and 2) keeping the number of activities to a manageable level.
I will like to hear your thoughts on this view and approach.

Cheers

Jose

Hi all,

Just this few weeks i have tranfered to other company as a planner obscourse and they have ask me to make a programme for a small warehouse and the planning manager ask me to put the end date of the project which constrained almost all the activiries, and when i submitted the programme he saw the float on some activities are less than 5 so he told me that if the float are less than 5 i shoild consider it as critical and so i did, now the result of my programme is all critical...but they also keep on insisting that number of critical path shoul only be 20 to 30 % of the total duration...any idea or comment regarding this method guys?

Best regards,

Joseph

hi guys....

remember that the critical path will depend on the logic that you would create on the activities............

there is no required % of activities in a programme for a critical path..........

you have the full control on how you would create the programme......

be logical on your links dont overdo your links

So Tom then you also say, That the planner should now, whats normal in his schedule towards critical activities. And when the output shows something else, he should look into his schedule to see what’s right (or not)
So dont just relay on the output of your schedule but try to look at the output from the users (builders,managers, etc) point of view. You cannot give one answer because it highly debends on what you’re planning.

Kind Regards

Henk

Hi,

Your critical path will depend on how you link your activity to each other, and so your critical path will depend on it.

Mabuhay,

joseph

I think the point is what do you want people to read out of your planning and critical path.
One thing is for sure. When the manager asks you what the critical path is he dont want to see 50% of the schedule.

So i think a good planning shows a critical path that gives you an idee what are the most important activities that are responsible for the project duration.
When there are to many activities you better start being creative with the software (works for me)

Kind regards
Henk

I have seen many scheduling specifications that require the Baseline Schedule to have no more than 30% critical activities and no more than 50% near-critical. I have never seen a specification detailing any percentages of this type for schedule updates. Good luck!

Charleston is right - could be 1 or could be all of them!