CROSS Safety Report
Columns missing due to 3D modelling
This report is over 2 years old
Overview
A new eight storey residential concrete frame building was being constructed and several columns were omitted from the ground and first floor level drawings, says a reporter.
Key Learning Outcomes
For civil and structural design engineers:
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A strict quality control system that includes the checking of drawings can avoid errors and near misses like this from occurring
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Consider introducing a quality control system that ensures the checking of drawings has been conducted in 3D as well as 2D.
Full Report
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The Full Report below has been submitted to CROSS and describes the reporter’s experience. The text has been edited for clarity and to ensure anonymity and confidentiality by removing any identifiable details. If you would like to know more about our secure reporting process or submit a report yourself, please visit the reporting to CROSS-UK page.
A new eight storey residential concrete frame building was being constructed and several columns were omitted from the ground and first floor level drawings, says a reporter.
Without the columns, a 225mm thick reinforced concrete 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.
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 Building Information Modelling (BIM) modelling software as the reason for these serious omissions. Is the use of 3D modelling a distraction to producing clear, accurate and well thought out construction drawings?
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Feedback
This issue is something I have been debating and discussing with our own BIM manager for a while. It is my view that engineers have become too remote from the current 3D software, as it is far more complex than the 2D cad in which we were able to dabble. It means that there is less engineering input to 3D models than there would have been with traditional drawings.
In effect the model is owned by someone skilled in operating the software rather than skilled in engineering. Despite having been involved with 3D drafting for the best part of 18 years I now find it very difficult to check 3D model output. I usually need to look at 2D drawings, which are vulnerable to error if they are sliced through the model at the wrong point, because they potentially don’t show features above or below the model slice. This is particularly true if there are changes in level or angle to a floor. There is also increased risk of error due to the fact that each element of a model now has to be given attributes, for example the concrete grade for columns. This might previously have been covered by a single note on a drawing whereas now the attributes of each column at each floor must be checked.
I have also noticed a recent trend where clauses are inserted into our contracts, which legally enforce the pre-eminence of the model over the 2D drawings and other aspects of the contract. I view this as dangerous, particularly as it is the drgs that engineers tend to check, not the model. I always seek to have such contract clauses deleted. I offer these thoughts not as a luddite trying to turn the clock back; I see many positives working in 3D and I am wholly in favour of adopting new ways of working. It is the inevitable future that 2D drawings will in time disappear. My fear is that in the transition period [which we are currently in] we have the tools and ability to produce models, but not the expertise or protocols to check them adequately or at least to the same standard as was common in the 2D world. We are currently looking at ways to improve this; but we are not yet there.
Expert Panel Comments
Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.
This report has generated a lot of comment from our Expert Panel. Is this a case of the following:
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.
Are different models leading to confusion during the review process?
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.
Who is responsible for checking BIM models?
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.
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
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.