CROSS Safety Report
Canopy collapse due to snow
This report is over 2 years old
During bad weather conditions in the winter of 2009 a school's canopy collapsed.
Key Learning Outcomes
For civil and structural design engineers:
Connections can often be the weak link in structures and attention to detail is required
An attribute of ‘safety’ is to assure that the design is not disproportionately vulnerable to minor error
Careful consideration should be given to canopies that abut adjacent structures, and there is a potential for snow drift to occur
For building owners/managers:
The specification of any inspection and maintenance requirements for fixings should be considered and recorded in the operation and maintenance manual
Fixings may require a combination of regular visual inspections with full inspections at appropriate intervals. They should be inspected by a person who is competent to do so.
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During bad weather conditions in the winter of 2009 a school's canopy collapsed (Figure 1). Luckily, the school was closed at the time and no pupil or member of staff was injured. The cause of the collapse has yet to be identified and may relate only to this cantilever type of canopy.
The incident occurred following a period of snow and ice and may also relate to the extra weight imposed on the structure by this.
The reporter’s team is now looking at a number of similar structures across the same Authority. The team also asks if anyone has experience in their own Local Authority of applications being made for these structures and if anyone has had any similar problems.
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Expert Panel Comments
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Whilst the cause of this collapse is unknown the forthcoming Institution of Structural Engineers Guide on Robustness discusses the issue of sensitivity to design assumptions. There is clearly some uncertainty in snow loading on small areas like this with the possibility of drifting and snow accumulation.
It is a sound approach to assuring robustness that the structure does not suffer a gross change of state if one of the design loadings is marginally exceeded. You can search for safety information on snow related collapses on the CROSS website.