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Location conflicts cause productivity loss

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February 21, 2008

 

The basic assumption of location-based planning is that working continuously results in higher productivity. Multiple crews working in the same location also result in decreased productivity and increased risk because resources might leave the site and return late.

 

In my PhD research I collected progress data from three projects weekly. All the projects showed the same result. If multiple crews are working in the same location, work either slows down or stops altogether. Slowdowns and stoppages happened even if the tasks did not have technical logic link with each other. Many tasks can be done in free sequence but they can not be done at the same time in the same location. For example floor covering work or plasterwork interferes with any other trade working in the same area.

 

Figure below shows a typical example from one of the case projects showing interference. Notice that the actual slopes of all of the tasks are very close to planned slope but only if the tasks can keep the complete location to themselves. Immediately when tasks happen at the same time in the same location, work either stops or slows down considerably. Average productivity loss is 20 to 50 % depending on the particular mix of tasks. In a project of 15 000 m2, I identified over 350 issues where productivity was lost because of these conflicts. It was also scary to notice from meeting memos that subcontractors had the same crew on site but achieved 50 % of production rate when there were conflicts. Think about the effects on subcontractor bottom line...

 

 

What are the implications for planning?

  • CPM is not a valid planning technique because slowdowns and stoppages happening in locations even without technical precedence have larger effect than a delays on critical path (will be shown in my PhD)
  • Buffers are necessary to keep trades far enough from each other
  • Weekly location-based controlling is required to achieve productivity benefits and to prevent trades from clashing

 

For subcontractors, this will affect the bottom line directly. For General Contractors, project contractual milestones become easier to achieve because each task can be produced faster. Schedule risk of the project will decrease because slowdowns and stoppages are by nature unpredictable. Some of the time saving is required for buffers but at least 10 % duration reduction is possible without increases in risk level. Alternatively the same duration can be achieved with much lower risk.

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COMMENTS

Hi Olli 
 
Great stuff. Your research opens up the big conundrum about exactly how CPM and BIM and VCM with interlinking databases relates to real world activities both the proposed and more importantly with actual feedback as its happening or worse when it is not. 
 
How many times have we all seen the stupidity of a manipulated CPM flowchart of a project in crisis to try and hide a major on project problem then everyone runs for cover when the balloon goes up. 
 
I think Mark sent you some of our views on this but just in case http://www.ideapete.com/workinglogic.html. and more importantly after that http://www.ideapete.com/6-dimensionalmodeling.html 
 
Its interesting to note than in corporation document workflow efficient ( and inefficient ) processes can be modeled assessed and more importantly monitored from actual operations but somehow when this moves to the infrastructure surrounding that dataflow and where its really ( or the building that its happening in ) we forget all the rules that the efficient digital workflow taught us. .  
 
Buffers are also intriguing because you are taking about space pauses in operations that impact other actions and could affect them even unseen ( Team 1 has a personal relationship to team 4 but its not shown ) ( Team 6 has Islamic members and this work is scheduled for Ramadan etc ) . This could also be feedback ie: this part of the job has a defect and needs to be rectified before this function starts. Taken further it could be crew or company location issues, crew training, have they seen the design data, did they agree and a myriad of other issues and last but not least does this task action amplify the clients REAL needs ( covered in a blog post to Mark and Dan ) , oppose it etc. 
 
What would be really neat is to take your static chart conclusions and then use the cloud or Constructor with hooks to add multiple dimensions to your research and bring it alive and then take similar data from active good and bad projects to develop best practices. 
 
Here is our view of the future http://www.ideapete.com/AATG.html 
 
Marty Golobitsky http://www.math.uh.edu/~mg/ who did the " Patterns Patterns everywhere " had a wonderful saying I believe attributed to Rene Thom " " When you build a model its really just a theory and may have nothing whatsoever to do with the real world except in the opinion of the modelers " Doesn't this match perfectly most CPM ( nas Maybe BIM ) that you have seen 
 
Again great directive thinking about real world validity, keep it up. 
 
 
( : ( : pete

posted @ Monday, November 03, 2008 6:57 PM by pete baston

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