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645 Response to report 614 on missing columns from drawings

Report ID: 645

Published: Newsletter 57 - January 2020

Report Overview

A reporter shares their views on how to implement robust checking systems for BIM models.

Report Content

A reporter was very interested to read CROSS Report 614 on drawings that contained missing columns and wanted to share their views on the issue. They agree with the CROSS Panel's comments that it highlights the need for drawings to be checked by a competent engineer.

The reporter believes that errors often manifest themselves in the drawing and the subsequent checking process, and not in the design. In report 614, the columns may have been missing from the BIM model used to create the drawings, or they may have been included in the BIM model but were terminated at the wrong level. In the latter case, the base of these columns could be terminated above the slab and therefore above the cut-line for the view that generates the drawings, meaning that the columns would not appear in the drawing for that slab level even though they were in the model.

The reporter says that one way of checking is to overlay the column layout from the BIM model with the column layout in the structural analysis model. However, a column which is simply missing from the BIM model may not be identified as the checker might wrongly assume it is obscured by the column from the structural analysis model in the same location.

The reporter believes that a more robust method of checking is to export an IFC file from the structural analysis model to the BIM model, where it can be imported as a 3D file in a different colour and the model can be interrogated more fully than a 2D DXF layout permits.

They go on to say that the method relies on the model being created perfectly, as any small errors mean that an element becomes corrupted and so doesn't copy over into the IFC file. The reporter encountered this on another project, where none of the walls and some slabs didn't copy over into the IFC file because of miniscule geometric imperfections. There may be settings within the software that enable this to be overcome, but the point serves to highlight the need to enhance our knowledge of how to use the tools as much as maintaining our core competencies.

For the reporter, the near-miss in report 614 highlights the importance of a robust checking regime. If a quality control system had been in place prior to this project, then the near-miss may have been avoided. In their view, a quality control system is not just a paperwork exercise, but if done properly, acts as a guide to help an organisation avoid errors. It also highlights the importance of rigorously checking the drawings; these are, after all, what the contractor uses for building.

Comments

The reporter is thanked for sharing their views on how to implement robust checking systems for BIM models. All designers are potentially fallible, and it is prudent from a commercial and safety perspective to have work properly checked. Moreover, a fairly regular theme in CROSS reports is one of how easy it is to miss a gross mistake like the missing columns in CROSS report 614.

Part of the issue during checking is the desire to go from 3D back to 2D because we have been programmed to view in 2D and see in 3D. As 2D drawings are used to build from on site, some basic checking in 2D is required, but now that the 3D tools are available, should better use be made of them for checking?

One CROSS member worked on a large steel frame building project where BIM was used but all checking was done in 2D. It was only the diligence of the 3D CAD technician that showed that how a complicated part of the structure did not actually work. In the world of 2D, this would have been missed and would probably have led to heated discussions during construction about who had responsibility for final geometric co-ordination.

CROSS would welcome better guidance on this issue so that there is a way to show that checking has been conducted in 3D as well as 2D.

 

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View other CROSS reports published in Newsletter 57


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