Estimating Activity duration in building project

We all know that estimating the duration of an activity is far more complex than simply dealing with 'canned' production rates, therefore the inherent complexity shall be considered in order to get good enough models. Because P6 and MSP lack the capacity to create such models many of us prefer to use more functional software.

Impact of variable but predictable working conditions such as the change of season shall be considered in any model. The following is a sample schedule where activity duration is determined by the season. While the crew is the same the productivity is reduced during the winter as well as the work hours. Attempting such adjustments using manual methods in large resource leveled projects is not a practical approach when the computer can do it.

Fortunately creating such models is easier than getting reliable estimates of production rates.

Patrick, in any case people and norms estimate resource/crew productivity and this is the basis for estimating activity duration when volume of work is known. For some activities duration does not depend on assigned resources.

If certain activity type meets many times in the project model and the same crew does them all it is reasonable to estimate duration of activities of this type basing on the same estimates of crew productivity.

If risk simulation and management is applied then it is necessary to estimate optimistic, most likely and pessimistic values of resource/crew productivity and composition, volumes of work, activity and resource calendars, and a lot more.

Estimating the duration of an activity is far more complex than simply dealing with 'canned' production rates! For a discussion on the subject see: http://www.mosaicprojects.com.au/WhitePapers/WP1052_Time_Estimating.pdf

Unfortunately P6 does not have activity volume and resource assignment productivity fields and does not do calculations that you need.

It is a pity that you are not able to select and to use the software that better fits to your requirements.

The following schedule is what you will get if you fix the resource quantities with an availability of 9 Resources A and 9 resources B. It will be inefficient and will yield the resources idle for too long.

The following schedule is what you will get if you allow the model to automatically adjust resource quantity and activity duration taking in consideration the relationship with production rates. The schedule duration will be substantially reduced and idle resource time will be reduced and perhaps eliminated.

So easy to implement that all is required is to specify resource productivity, minimal quantity and mark quantity as variable, the computer algorithm will do the math for you.

Vladimir,

The driving resource approach we use frequently with variable quantities as for the activity be scheduled to start as soon as a minimal amount of the required resources are available and to increase the quantity as soon as there are more available.  Anyway this is how even a rookie PM will react in the field if the plan is not good enough to consider these scenarios. No PM is to delay the start of such activity because out of 10 planned resources only 9 are available.

Of course there are many occasions in which it is easier to use the driving resource approach, but not always this represents crew behavior when composition changes. The same resource might still be driving but the relationship to crew production rate as a whole might not be linear and this shall be considered by the model when this might happens and is predictable.

When crew productivity is not in linear relation to a specific/driving resource quantity we use a multi-resource to represent the crew, then by using Skills on the multi-resource the best available crew along with its adjusted production rate will be automatically selected.

All makes sense, all is easy and transparent.

Best Regards,

Rafael

Rafael,

when crew productivity is defined it is expected that crew productivity was calculated for current crew composition.

But yes, crew composition does matter and that is why we suggest to assign productivity not to the crew but to driving resources belonging to the crew. In this case crew productivity is the sum of productivities of its resources and will change together with the changes in crew composition. 

• Composition do matter:
  • An operator and and a small excavator cannot dig at the same speed as the same operator using a large excavator.
  • An operator will produce the same as two operators if there is only one excavator, the second one will be idle.
  • 10 bricklayers will install more bricks per hour than 5 bricklayers.
  • If resources are not available the activity will be delayed until enough are. If you do not consider resource availability there is a high risk the plan will be unfeasible.
• Working conditions do matter:
  • The same crew working at night might have lower productivity than if working during the day.
  • The same crew working on summer might have higher productivity than at winter.
  • The same crew working 4 continuous hours per day might have higher productivity than if working the same hours but intermittently.
• You will get better models if the variations in crew/team composition is included in your model for it to dynamically react to predictable changes in composition due to changes in resource availability as well as to changes in working conditions.

Spider Project is an advanced project management software that is used everywhere in Russia and in 34 other countries.

It is the only PM software that works with activity volumes and resource productivity and so automates calculations you are looking for.

Spider Project is an integrated software that includes everything project planner may need - scheduling, budgeting, advanced resource management, risk simulation, portfolio management, etc.

Demo version of Spider Project with 40 activities per project restriction may be downloaded from www.spiderproject,com. You may also look at Spider Project forum here at Planning Planet.

Regards,

Vladimir

Siddiq,

if activity volume is 2000sqm and crew does 90sqm per day then the job will take 2000/90=22.2 days.

You set productivity for the whole crew. Another approach - to set productivity for the leading resource of the crew that defines the productivity of the whole crew. If this resource or the crew works on activity part time (for example 50% of work day) then resource/crew productivity is lower (45sqm per day in our case) and activity duration will become longer (44.5 days in our example).

This is the way activity duration is calculated in Spider Project when you enter activity volume and assigned resource/crew productivity.