Vladimir,

What you say is true, but Sabu has already told us there are no lags on either the FS or FF relationship.

Sabu,

To try and return the discussion back to your original question, there is no logic to having both an FF and FS link between 2 activities. This is an error.

Whilst both links are there, the FS link will automatically take precedence in all situations, other than this one exception:

 Predeccesor activity has not finished, but successor activity is in progress (i.e. out of sequence working), and you are using "Progress overide" scheduling option. In this case, Primavera will ignore the FS link, but comply with the FF.

Cheers,

G

Planner's brain, software and experience are all important but none is a substitute of the other, they complement each other. If one is broken the chain is broken.

If you do not use software to plan then software does not matter, this I can understand from people who do not get involved into the details. But for people who use the software to really plan the software matters. Some go as far as integrating the software into their accounting, an outsider telling them what software to use because make it easier for him is non-sense.

Volumetric calculations are the day to day concern of every Project Manager, the man who is in charge and who needs this information. If his software provides for volume of work then the software can be integrated with all the remaining modules such as Unit Job Costing, Payroll, Purchase Orders ..., otherwise you just get mere budgeting, good for top management but not good enough at the level where true action is, at the project level, where transparent production [volume of work] and productivity [volume of work per unit of time] metrics are of concern. For large jobs use of Excel is like using an Abacus, you need something better to tame productivity.

Rafael,

It is because of detailed design development, say for an EPC project.

Volumetric calculations can only be derived from detailed BOQ, and I guess using Excel is much easier for tracking volume of materials or works.

Activities with volumes to be measured against time is too complcated that you will need a detailed BOQ in place in order to develop a time schedule, and this is not possible in EPC projects where sometimes design development is going in progress with construction at the same time.

I'm certain that Dieter is not only IT projects.

cheers!

Dieter,

Planner's brain, software and experience are all important but none is a substitute of the other, they complement each other. If one is broken the chain is broken.

I can see you are on IT projects therefore P6, setting bugs aside, can be an option but I cannot understand how construction schedulers can work without volume of work and productivity based on volume of work.

How you measure volume of work and productivity on an IT job is different to how you measure volume and productivity for construction works.

It is not about labels, like P3e vs P3ec [c for construction].

P3ec was missing volume of work and productivity in the construction language! P6 no matter how you label it was designed in its core logic for IT jobs, adding good functionality for construction work means serious surgery, a band aid wont do it.

At the end of the day the very first thing a PM does is check on the productivity, how much concrete per mh, how much earthwork per crew hour was poured today. If his software lacks functionality to track and manage productivity the scheduler will be blind, the CPM will be a very limited tool to project the effect of productivity trends.

Rafael

Volume lag represents a distance that is converted to an equivalent and variable time duration. If your reported volume of work is slower than planned this means the equivalent time lag is increased.

Say for example you require to keep a distance between the drywall and painting of 100 lm of wall but your production is such that at a point your walls are 200 lm ahead, this means you can instantly paint 100 lm of wall and then keep the pacing.

On the other hand if the production of drywall is reduced to less than 100 lm difference the painting must be stopped or the production of drywall shall be speeded or the crews will collide. An out-of-sequence flag will warn you about the problem.

Also if your activities are volume of work and the links have volume lag as you change crew composition and productivity the duration of activities as well as the lags will be adjusted accordingly.

If you increase the Drywall crew as to produce twice the walls on any given period the activity duration will be reduced to half as well as the lag. You will need half the time to keep the distance.

Remember that crew composition might be a function of resource availability that changes with time, you want to make use of available resources and avoid keeping idle resources when they can be accommodated to productive work. It is a functionality that works in conjunction with others, including the resource allocation and variable quantities and workloads.

I don't believe you can easily substitute a volume lag with an activity, not even with a production type activity as the work is done by the predecessor and not the activity per-se. Volume lags are a must have functionality.

The best way to understand it is by following a model using Spider Project as many of these functionalities are lacking in P6 and compare to how you would model such scenarios using P6.

The following figure shall be enough to illustrate a simple scenario.

calendar 1 = 6 work days/week

calendar 2 = 7 days per week

Some people have suggested that to provide for software limitations you can use activities instead lf lag, but it can duplicate the number of activities and so the number of items to update. Activities and links are not 100% interchangeable at least not with regard to updating.

It is not difficult to figure out in the model same as we have 2 FF links we shall have 2 SS links, yes a few are missing. If this is modeled using activities it would mean that instead of 2 activities and 4 links we would need 6 activities, with 8 FS links to make the substitution on each original pair.

Also want to mention that usually the correct lag type to keep distance between crews is volume lag while to keep curing time is time [sorry for the redundancy]. But the concept of volume lag is usually not understood by those who use software that have no such functionality.

Time lag is automatically consumed while volume lag consumption is a function of realized volume of work, it keeps active until all volume is realized, therefore can flag an out-of-sequence event as you progress your activities warning you that some corrective action is needed.

That time elapsed does not means you have realized enough drywall to start painting, a relationship or distance you shall keep at all time. Ironically at all time means avoid using time lag and use volume lag.

Fortunatelly not many activities require the modeling of curing time while some require the modeling of volume lag.

Rafael

Weird that P6 does not allows to link two activities twice with the same type of link.

That two links are of the same type does not makes them equal, the can have different lag and different calendars, depending on when the lags become active one or the other might be the driving link.

sabu,

I ned your answer to Mike's question in order to make further comments.

Rafael

Hi Sabu

Are the FS and FF links coming in from the same Predecessor?

Best regards

Mike Testro

These are basic link types but I will assume that you are referring to the special situation were you model some activities overlap by linking two activities using SS and FF links with some lag.

Although time lag is different to volume lag some software use time lag because this is all they have.

Usually the better model will use volume lag to keep a distance between the two activities. This is a better modeled that uses volume lag that will be active until all volume is realized. Time lag is consumed with the passage of time, can happen before required volume is realized and therefore does not warn you of out-of-sequence progress for volume of work. It is simple, that some time elapsed it does not means the volume of work progressed accordingly, you must follow up on volume of work to make the appropriate adjustments in your crews,you got to manage your schedule, your productivity.

You need the SS+lag to establish and control the distance while the FF+lag will keep the float calculations.