CROSS Safety Report
Questionable tension bracing arrangement
This report is over 2 years old
Overview
A reporter is concerned about the arrangement of diagonal tension bracing in one bay of a building.
Key Learning Outcomes
For construction professionals:
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If structural modifications are required due to lack of fit issues on site seek approval from the design team prior to making the alterations
For all built environment professionals:
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If you notice a potential safety issue not during the course of your work, consider reporting it to the owner or tenant
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If the owner is not known, then the appropriate regulator could be informed
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A reporter is concerned about the arrangement of diagonal tension bracing in one bay of a building. The connection is formed of four stainless steel bars connected by what looks to be a circular plate. The bars are out of alignment due to incorrect measurement or poor fabrication. To make the connection fit, the ends of the bars have been ground down and the plate skewed resulting in an eccentric loading arrangement.
In the case of a brace under tension, the plate will rotate about its centroid due to the eccentricity of the tension force. The resulting rotation will force the opposing bars into compression increasing the likelihood of the bars buckling - all the more critical if the length of the bars is not as designed.
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Expert Panel Comments
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Another case of a third party picking up on a potential fault. The arrangement of the members is not unusual, but it seems to be a case of the installation not matching the design, and possibly the assumptions in design being breached. No connection is perfect in alignment, but a good robust design will cater for some deviations.
If the members have needed to be altered on site to make them fit, that should have been the trigger to ensure the design was still valid. Any steel structure is only as good, or as safe, as the integrity of its connections. Hence the principal designer must be assured that the design intent overall has been correctly translated into reality.
If the members have needed to be altered on site to make them fit, that should have been the trigger to ensure the design was still valid
However, has the reporter raised this with the building owner? There is no legal duty to do so but as a matter of good ethical practice an engineer who notices a potential safety issue would advise the owner, or tenant of their concern. If it is not known who this is, then the local authority could be informed. Where there might be an immediate and severe risk, then CROSS may be able to advise on a course of action.