The "Critical Path" extends from "Today" (the data date) to the end of the project. Due to the dynamic nature of daily CPM activity, the critical Path can switch daily for one chain of activities to another and back again the next day. Each day, there will be a critical path (but not necessarily the same path.)

I am saying that the only thing that the critical path has in common from one day to the next is that ON THE DATA DATE, a certain set of activities were both critical and active. This is the only thing that matters. Note what was critical on any date. Add all of the dates together (one at a time) and you have a list of critical, active activities. This is the only truth.

The daily critical ’path’ may hop from one chain of activities to another without a logical relationship between then to ’model’ it. The ’critical path’ may actually hop between two or more activities as they progress. It does not matter. Each and every day, something is critical and active. All of the rest is either unknown or planned.

Don’t focus on one single critical path. Instead, focus on what was critical and active on any given day. The difference between the two is the difference between classical CPM theory and the truth.

Ron Winter.

Jaco - Yes, you can compute the CPM for completed activities but do not forget that the CPM is computed using activity remaining durations. The remaining duration for a completed activity is zero. This does not tell you much about the critical path in the past.

Philip - You are correct ahout ’hindsight’ but what about ’Today’? You can certainly tell what is critical today. Tomorrow will eventually come and when it is ’today’, you will be able to determine the critical activity for that as well. My point is that for any given date, you should be able to state what was critical for that date - even for dates in the past. I have not said anything about the Critical Path - only the critical activity for any given date.

Hi Ronald

I was looking at your paper and was wondering why can’t you calculate Float on activity’s that is completed. Remember you can change the dates to Non dates (numericals) even though computer systems don’t calculate float in activitys that is in the past you as a person can calc it manual.

I know actual should not have float but to do an as Build Critical Path you must calculate the float manual.

You can do a forward and a Backword pass on actual start & finish dates

Cheers

[Duplicate entry deleted.]

Hi Gerry

Please Explain

Is it not the case that the piecemeal working and intermittent effort upon the activity (especially the kind of activities that Jaco mentioned earlier) seriously compromise the insertion of logic into an *as-built* programme.

Dear all,

This has become a very interesting thread. I would like to return to something that Roger Gibson said earlier. Assuming that Gerry is undertaking some sort of a delay analysis, or is preparing a claim, then that is why he is considering an as-built critical path approach.

In so doing, Gerry also needs to consider what Roger described as the “windows” approach. I concur with Roger, in that it is my preferred method of analysis as well. The reason why is this…..

In producing an as-built critical path programme, you can see what was the longest critical path chain throughout the project as it was at the end of the project. This is fine, but it lacks one vital consideration. The problem is that it considers the project only after it is completed looking back, but ignores what was known about at the time. Let me give a very simple example. Let’s say a house is being built and there are problems with building the foundations. The design is late and this causes a 3 week delay. This is on the critical path and an extension of time of 3 weeks is quite properly given. All quite straightforward and simple.

However, the design also incorporates a swimming pool in the garden, which is a contractor designed item. At the time of granting the extension of 3 weeks due to the late foundations, the swimming pool excavation is on programme and all seems okay with the pool. But, the contractor takes far too long to design the pool and order the water treatment equipment and this turns out to be the eventual cause of the house being completed 10 weeks late.

So if a retrospective as-built programme was drawn, it would show the as-built critical path going through the swimming pool, but not through the main house foundations.

Would you say that this as-built critical path programme was correct? It does, quite correctly, show that the eventual critical path went through the swimming pool, but some would argue that it would ignore the true cause of early delay – the house foundations. This is where a “windows” approach is preferred by some courts, because the windows approach, as Roger has stated, considers what was critical AT THE TIME. This is the important point. An as-built critical path can only consider what eventually turned out to be critical, but doesn’t consider what was known about at the time.

So, Gerry will have to bear this in mind when (if) he produces his as-built critical path. There are drawbacks to this system, as there are with most.

Gary France
Chairman
Planning Engineers Organisation

I think Uri is right in general to make As built critical path Schedule. But if you want to keep As built Schedule for future reference of planning then we should consider only those delay points which generally happens in project to identify the critical path. I mean to say that if the delay something like unavailibity of fund or vendor’s bankrupt comes on critical path we should ignore that to say that is not the critical path even though that will be longest path. Then we can say second longest path is really ctritical for future reference of planning but for cliam purpose the longest path will be considered.

Yes, critical path is most commomnly used term in planning and also it is the longest path based on the correct logic whereas "As Built Path" is not commonly used and not depenable.

My answer is yes.

An as build longest Path can be produced. I would suggest to forget about the logic issues. Please note the diffinition of a critical path is the longest path. Not the longest path due to logic. With other words if the logic is wrong (We are all human) the critical path is something else than the longest path.

But why do you require this. I am not sure what type of project you are working on / or refering too.

Cheers

Gerry,

Personally, I don’t think an ’As Built’ critical path with true as built logic can be created. Just because activity B started 3 weeks after activity A started does not mean that the as built logic between these activities is a start-to-start of 3 weeks. It could be because of a number of factors, e.g. shortage of resources or awaining information.

In carrying out a retrospective analysis of actual delay my preferred approach is a series of progress snapshots, or ’windows’, which show which activity was critical at each snapshot. From this, and further investigation and interrogation of the network, progress and other records an ’As Built’ critical path is established.

Roger Gibson

Gerry, Whilst it is acceptable to change the logic by adding links in creating an As Built Critical Path, it is important to justify and explain the reasoning for each change. Another important ’verification’ check of the As Planned network are the activity durations. I have often seen eot/delay calculaions based on original programme durations that were excessive and therefore resulted in eot/delay calculations being longer than reasonable or realistic. Roger Gibson

Gerry,

Gary is right that you have to take care when you add in retrospective logic – hence my caveat about ensuring that there are no inconsistencies with the original logic.

In principle, however, provided that your logic is sound and reasonable, there is nothing inappropriate in inserting retrospective logic (subject to the points that Gary and I have made).

Cheers,

Stuart

www.rosmartin.com

Gerry,

Provided that the logic as inserted is not inconsistent with the other related activities, there is nothing wrong in adding it into as-built already-constructed activities.
This happens all the time when trying to demonstrate that a Delaying or Relevant Event (call it what you will!!) has had an impact on the CP.

Hope this helps

Cheers,

Stuart

www.rosmartin.com

Gerry,
It is essential that an as-built CP is developed if an argument arises over EOT to a Contract.

The as-built CP will sequentially trace the work activities that were executed for the project to reach completion, or up to the time under consideration. If completion is reached, or shown to be reached, later than originally planned, then you have a delay. If all or part of that delay is attributed to reasons not applicable to the Contractor, then the Contractor may be entitled to an EOT, which may equal all or part of the delay.
Subsequently the Contractor may be entitled to costs related to the EOT.

But the foundation for all of this is the as-built CP. If the Contractor cannot demonstrate that the as-built CP was pushed out for reasons not attributable to himself, then he cannot claim an EOT.

And remember that an as-built CP is not just the final one produced at the end of a project; it is the CP that has occurred from the start of the project up to the time in the schedule under consideration.

Cheers,

Stuart

www.rosmartin.com

Dear Jaco,

What you have said is correct, The longest path is the critical path. As Built Critical Path is based on the actuals happening at the site i.e. based on the actual update; when the project is in progress due to the rate of progress of work experienced at site the original critical path(or the baseline critical path) could be altered and may be at the end of the project a new longest path could be found than the expected one. Once the project was over we can say it as a As Built Schedule just like saying as-built drawings. The As built schedule should reflect the history of the project in genuine. Obiviously the longest path formed in the As-built schedule would be a As-built critical path but not necessarily to represent the original baselined critical path.

Regards

Daya