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614 Columns missing due to 3-D modelling

Report ID: 614

Published: Newsletter No 45 - January 2017

Report Overview

A new 8-storey residential concrete frame building is being constructed and several columns have been omitted from the ground and first floor level drawings, says a reporter. Without the columns, a 225mm thick RC slab was being asked to span up to 14m.

Report Content

A new 8-storey residential concrete frame building is being constructed and several columns have been omitted from the ground and first floor level drawings, says a reporter. Without the columns, a 225mm thick RC slab was being asked to span up to 14m. Some of the missing columns were spotted by the concrete frame company's project manager. Others were not immediately obvious due to transfer structures and column plan positions changing up the building. Consequently, these columns were not built by the contractor, who continued to prop off the slab in the usual way during construction of the upper floors. The consulting engineers cited the use of BIM modelling software as the reason for these serious omissions. Is the use of 3-D modelling a distraction to producing clear, accurate and well thought out construction drawings?

Comments

This report has generated a lot of comment from our panel. Is this a case of user incompetence, lack of experienced engineering supervision, lack of checking, lack of ability to understand conceptual design, or all of the above. It would be hoped that any engineer would spot such gross errors in his/her checks, yet in this case it was missed. BIM is a great tool to assist with sequencing and fit, but it must be operated or overseen by experienced engineers who have a full grasp of conceptual design and can recognise fundamentals such as columns being missed. Whatever the system clear, accurate and well thought out construction drawings are an absolute necessity.

It is not stated how the issue arose with the 3D BIM model. However, it is possible that the BIM model used different software to the analysis model. It is becoming more common to import the analysis model into the BIM model and when this works the advantages are clear but in many cases the imported model needs tidying up. It is unusual to lose complete elements but it is possible that the columns were deleted by someone not appreciating their structural role. The BIM model would likely have been a multidisciplinary model and there is the possibility of another discipline inadvertently deleting the columns due to clashes with their elements. Structural Engineers need to appreciate that they are still required to check the final output regardless if this appears to simply be a copy of their analysis. As BIM becomes more common Engineers need to improve their skills and develop tools to check final BIM models against their design intent.  It is they who are responsible for design not the software. 

On a wider theme, the history of failures reveals a frequent pattern of gross error: that is an error so bad, you wonder how no one spotted it. This report seems to fall into that category. A lesson is for engineers to always start with looking at the big picture: are the load paths clear, is there a stability system and so on? - all before they get down to detail.


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