Rafael Says Let’s Challenge Mike.

Hi All,



Allow me to refer to Mike’s post no. 16:



1. "Are you saying that you arrange your work so that rebar fixers - electricians and plumbers are all working in the same place at the same time? I don’t think so".



2. "The rebar fixers will complete the bottom section and move on - the conduit fixers will follow and then the rebar fixers will return for the top layer."



For No. 1 (If I’m allowed to answer), I’d say yes! This always happens before concrete placement and you are running after the inspectors to sign your pouring request!



For No. 2 - Ideal but not always the case, because conduit fixers tie their conduits on top layer bars sometimes (Mike, I thought you are a Builder???).



cheers!

Vladimir



Because of poor software capabilities.



You were correct when you inferred I do not level resources. I resource load the schedule to make sure our soft relationships “solved” the issue. This prevent us from unlevel the schedule, as a consequence we are missing schedule compression options.



Most of our Contractors favor the use of "soft relationships" because our software after resource leveling does not show resource critical path nor resource float, with the lack of this functionality float is meaningless under limited resources. You lose track of what is driving your activities.



Traditional resource leveling reports are kind of cumbersome and even hidden, some P3 and P6 users do not even know about these reports. SureTrak do not provide me with such a report.



Proper Implementation of Resource Leveling



The Contractor wants to see which activity was delayed by predecessor or by resource; resource critical path provides the answer visually on the spot, on every screen.



From the next link:



Resource Critical Path Approach to Project Schedule Management



“True critical path should take into consideration all schedule constraints including resource and financial limitations.”



Nothing, new, we know that, our software developers do not know how to get the resource leveling algorithm to tell what it did. Our software developers are going backwards, re-inventing the wheel, hundreds of definitions for date fields and a database with thousands of irrelevant fields but not much up-to-date functionality. They are a bunch of database managers incapable of any scientific thinking.



Best regards,

Rafael

Rafael,

so you also don’t level resources?

It is interesting who level resources. I have an impression that very few members of PP do it. Can this be explained by poor software capabilities, poor data, or there is some other reason?

Best Regards,

Vladimir

Mike



You got the right sequencing of trades. I was referring to the very common sequence you have when you strip your flying forms, one by one with a tower crane, it might be 2 decks per bay, 8 bays per day. You have 16 decks working in sequence, at 3 activities per deck this would yield 48 activities per day only for your elevated slabs, then for your walls you would get about twice, and so on, for a single days work and only for what is happening on the top floor, it is too much, your approach is not practical. Just imagine the printout for a single day’s work at your typical condo, something the contractor has been doing for many years.



Not all of my laddering are progressive feed but most of them, for progressive feed your best option is to use this functionality if available in your software, if not a progressive feed then your option would be SS and FF relationships.



“Your updating software is just a spreadsheet application that works with P3 or SureTrak where you can’t otherwise copy - paste the data.” - Copy and paste is so error prone that none of the serious scheduling software should have it as the mean for updating the whole thing, a more advanced technique is a better way to do it. Copying and pasting thousands of spreadsheet lines just to update a few cells is not an efficient way of doing things.



“I have listed the reasons for avoiding FF SS lags many times on PP before now and you and I and Vladimir have discussed them all. “ - For the moment I have not seen any valid reason on your part, on the other hand there are a couple very specific exceptions on the references I gave you before.



Your approach to resource leveling I find it to be practical. I use the concept of crews where a crew might be composed of various related trades, at times you do not know exactly your final ratio of masons to helpers and unskilled or labors but you know what size crew it will be. The crew will be working under the same supervisor for many weeks and the personnel are not to be moved from crew to crew on a daily basis. This is how construction works are managed, different to the matrix organization a design firm will use to manage their design teams where a designer might work for different jobs, for different PMs and a design trade supervisor. Here each person would be a single resource, each with a particular set of skills.



Best regards,

Rafael

Construction crews include people and machines, people have different specialities. Activity duration depends on assigned resource productivitries that may be defined by people productivities on some works and machine productivities on others. Changing crews you change activity durations and costs. For some machines like cranes their quantity is always restricted and your schedule shall take it into account. And it is nice to get from the schedule resource plans.

I think that defining activity duration you have in mind some crew that will do the work. Then you count the number of people in this crew and multiply it by activity duration. The result become resource Hours. If I am wrong explain what you do.

In any case not all resources in the crew are driving, some of them are not fully loaded, there are also machines, etc. And it is necessary to know the planned quantity of resources on site at different periods.

Best Regards,

Vladimir

Mike, you wrote:

Laddering looks good on the chart when all tasks are of a similar duration but the symetry goes when they are of different length.



If there are both SS and FF links then it does not matter if activities have different durations. With different durations one or another link will become driving and the works will be done continiously.



I don’t share your attitude to Resource levelling and am sure that Hours cannot be considered as Resource at all. If it is good for you and your customers then it is OK. Our customers are not satisfied with the schedules that are not resource loaded.



Best Regards,

Vladimir

Vladimir



It seems like Micro Planner have something similar, they call it "progressive feed", and yes this approach must be more practical and safer than using lag times. Use of lags will not be enough, SS and FF won’t prevent successor from slipping away. Progressive feed or Volume Lag is more than just a safe substitute for SS and FF, has a lot to do with resources and also with float even in the absence of resources. I know you know it but it is important everyone else get it, sorry for being redundant once again. I bet in your favor that they do not have the reports you have for linear jobs.



Mike



What about resource leveling, without resources there is no job? We got to admit Spider Project provides full CPM functionality into linear jobs like no other software. Why two software packages if you can do it with one? Especially good when you have a combination in a single job. Other Linear Scheduling software provides a lot of beautiful graphs at a high cost but not much functionality.



At times I have a need to keep several activities in a ladder with SS, FF and zero lag for activities that are incidental with another. As for example I might have an activity for placing of rebar on an elevated slab but at the same time the electrician and plumber got to be working in the same area. I need to separate them from the main activity for reporting and coordination with the trades. These activities must start and finish at the same time.



For updating our jobs we use Primavera Post Office, a mini application that can run stand alone. We filter the activities to be updated, a 3 month look ahead and e-mail the filtered Primavera Post Office file. This avoid sending the whole count and looking through a large number of activities, no need to send those previously finished or not in the horizon. When I receive back the file in my e-mail box I update the activities at a click of the mouse without need to make sure all activities are sorted out exactly as per my spreadsheet. Activity fields and resources can be updated as you can customize the table with ease. Sorry using a spreadsheet to update a CPM seems like archaic, no matter what gadget you are using.



Please help me with a list of lag traps so I can make a list for my use as to avoid them. For my laddering I will continue using SS and FF lag without the full functionality you can get with progressive feed, volume lags or ladder type activities, I have no other option with my software.



Use of lag other than laddering represent a mere 1% of my activity count but I am still concerned about this 1% (Total activity count x 10% activities with lag x 10% not ladders = 1% of total activity count).



Best regards,

Rafael

Mike,

we repeat the same arguments.

We already calculated the number of activities that are necessary in 1000km pipeline construction project if to use your approch. Dividing the project into small parts is bad idea. These parts are not independent.

And we also discussed that Tilos does not level resources, materials, finances. Maybe it is OK for your projects but not for mine. I chose linear projects because in this kind of projects using ladders is natural and obvious. You did not answer if you understand that replacing continious activities by discreete you make the simulate less accurate. It is your choice what to use in your projects but you did not suggest any real argument why other approaches are not as good.



Rafael,

I already wrote that Spider Project has so called Volume Lags and you can define that the next activity can start after 500m will be done on the preceding activity. This approach is much more practical and safer than using Time Lags. Besides Spider Project has strict links. Activities linked by strict dependencies are pasted and delaying next activity will delay preceding activity.



I don’t know if similar functionality is in MicroPlanner.



Best Regards,

Vladimir

To all:



Managing the Overlap: Where inserting an additional task is not appropriate, the nature of the gap needs to be clearly understood: Why is this lag needed?



Links, Lags and Ladders





Mike



Mike using percentage instead of remaining duration to update your job is usually erroneous; the software computation for remaining duration will usually come out wrong, in disagreement with true remaining duration. In order to get it right when using percentage duration, got to know actual duration and remaining duration; when linked, %complete = 100x (Actual Duration)/ (Actual Duration +Remaining Duration)



In addition you should consider the following;



PITFALL #1: Linking of Percent Complete and Remaining Duration



I find your approach as another way to model the same thing as if you divide a 30 days activity into two 15 days activities in tandem. Construction jobs at this side of the pond are required to have a scale with maximum construction activity duration of 20 days, waiver to this are accepted if justified and non construction activities such as a delivery are exempted. Our good practice protocols are based on this scale, lag is one of the issues our protocols pay particular attention. It can be that applying this protocol to linear jobs might spell disaster.



I was hoping for you to tell me why my model is wrong, the following link is from a book which its first edition was written over 40 years ago, still on the market but I wonder if up to date to 15 years ago after SureTrak update or service pack C. I believe most of the issues about lag in the US have their origin here, when this book was written and O’Brien was one of the pioneers. He was one of the proponents of constraining contractual milestones and project duration, allowing for negative lag and the cause of many headaches.



Lag Algorithm





In the link you will see an example of the traps in the use of lags, but I could not even re-create the trap in my model using my version of SureTrak following good updating practice. You are welcome to use it as a reference in your quest to invalidate the use of lags in my model. You are also welcome to show us other situations where the use of lag tricks the CPM computations, now we understand your model, let’s move to the next stage.



The idea is if there are traps (we know there are) in the use of lags, let’s go to the bottom of it. I am sure we can get a set of rules that will avoid most of the traps without banning all lags.



Vladimir,



With traditional SS and FF links you cannot fix the distance between two activities so related that if the second is delayed the first must slow down and is also delayed, resource allocation will follow. Probably your software can do that without resort to cumbersome relationships, I am sort of becoming lazy. The idea of having a definition for a SS and FF to create a fixed steps, equal rungs ladder is a functionality I would like to have. I don’t remember if Micro Planner ladder activities behaved in this way but believe it does.



Best regards,

Rafael

Mike,

we repeat the same arguments.

With your approach 1000 km pipeline model will have close to 1 mln activities and you did not try any project of that size with PowerProject. I don’t think that it will be easy to work with this model. And multiple activities on the same line do not add much to the way people work with the data. Besides your approach means that you replace continious work with discreet elements that creates unnecessary delays.



If you have objective (physical measure of the work performed then long durations do not create problems. If you know the direction of pipeline construction and know that 5km were done you know the exact point where the crew is at the moment. In this case activities may be longer.



So you will agree with Rafael if he will suggest 14 days example instead of 30 days example?



Best Regards,

Vladimir

Mike,

I did not find in Rafael post anything about long activity durations. More than that we recommend to restrict activity durations not by 14 but by 7 days and we still use SS and FF links.

The distance between construction crews at pipelinbe construction is usually 500 meters and the speed of construction is close to 500m/day. And it is easy to estimate where each crew is knowing the volume of work that have been done measured in physical units.



You did not answer Rafael’s question, you discussed other topic.

Mike



By subdividing CMU Partitions into 6 stages then you are opening the door for six out-of-sequence occurrences between CMU Partitions and Cement Plaster after it happens at the first stage there is no reason why it cannot happens during the next stages, most probably it will. Similarly with Cement Plaster and Paint Walls, is kind of complicating things. I accept naming the stages got to be fun.



From four activities now we got into 19, there’s got to be some justification for it otherwise is nonsense.



I never had problems with my updating except when out-of-sequence occurs, why increase the chance? We use the correct methodology in our updating, I don’t see any valid reason to increase the number of activities by a factor of 19/4=~5 and in addition increase the chance for out-of-sequence occurrences from 2 to 12 this yields a factor of 12/2=6 is kind of insane. In this regard I find the first model superior.



Can you be more specific about the progress updating issues your software has? It cannot be something you got out of an old book or someone told you. I want to make sure my software does not show this kind of behavior using our method of updating and calculation options. I would appreciate if you use my model so I can easily follow you; anyway you say it is wrong, just 4 activities instead of 19, is a bargain.



If I got a SS1 (one day lag) relationship how many stages will I get, what if SS0? If it cannot be 0, then Lim (lag --> 0) ?



Best regards,

Rafael

Mike



Let’s make it a model for CMU Installation, Cement Plaster and Painting something many must be familiar with.



Activity-Duration-Successors

A1 CMU Partitions -30d-A2SS5, A2FF5

A2 Cement Plaster-30d-A3SS10, A3FF10

A3 Paint Walls-30d-A4

A4 Misc. Surface Repairs-5d     



Show us how you will model the network using only FS0 relationships and at the same time all work on the activities kept continuous during any update, maybe at a variable rate, and of course all relationships maintained.



You got to consider activities no A2 and no A3 have other successors and that subdividing the activities in many small duration activities would never show true relationships as you always can further divide the activities as if you were solving a calculus problem. This would be nuts.



Finally tell us why the use of lags makes invalid the above model. Please be reminded that many of the traps with lags are related to updating, these can be avoided with the proper use of your scheduling options. As for example, do not link remaining duration and percent complete, this creates problems with lag on some old software versions, this is a lazy scheduler option as well as any other option that automates updating, the problem is in the options not in the use of lag. Keep as a reference your outdated CPM books but don’t take for granted all you read on them.



Best regards,

Rafael

Yes, it may be interesting.

If you will not be able to find a solution using PowerProject let me explain how to do it in Spider.

Best Regards,

Vladimir

Mike,

I understood that we discussed if SS/FF relationships shall be used in project modelling. Why PowerProject and software query?

Best Regards,

Vladimir