CROSS Safety Report
Collapse of a wall during construction
This report is over 2 years old
An internal corridor wall collapsed in a school under construction.
Key Learning Outcomes
For civil and structural engineers:
The design of internal walls should consider the construction phase and whether the design should be governed by this, rather than the in-use phase
If the walls have been designed for the permanent condition highlight this on the drawings and the risk register
For construction professionals:
If the construction sequence subjects internal walls to greater wind pressures to what they have been designed for, then this should be raised with the design engineer
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An internal corridor wall collapsed in a school under construction (Figure 1). The wall, when checked, was not to be unstable in all stages of its construction even when built up to the head, until the external envelope was substantially complete. Programme constraints indicated that the walls would always be built before the envelope.
A generic assessment of risk by the designer did identify propping masonry in the temporary condition, but, says the reporter, this was not clearly enough set out for the contractor to spot, though he should have questioned it.
There were a number of panels which were subject to temporary situations which were more onerous than the permanent conditions, but the one that fell was off-grid and had no intermediate supports being 37m long by 3.8m high. It was indeed fortunate that the site had finished for the day and no-one was injured.
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Expert Panel Comments
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It is common for internal walls to be subject to temporary wind loads that exceed those in the final condition. For the significant scale of the walls here, it would have been essential for the temporary stability issues to have been identified prior to construction, in order to minimize the risk of collapse.
Designers must eliminate hazards and reduce residual risks in a manner that contractors understand. They must highlight potential risks where temporary load cases are more onerous than the permanent case. They must also identify special cases where extra care is needed, and it might be thought that a wall of these dimensions was one of these on the basis of general building knowledge as well as of regulation.
Contractors also should be more aware of temporary situations and assess each trade package as it develops. A review of temporary works should be carried out on any project to identify any short, or long term, supports that may be necessary, backed up by engineering advice as necessary.
There is also the issue that programme changes may have been made without the knowledge of the designer who should always remain involved. Regulation 28 of ‘Construction Design & Management Regulations 2007’ covers stability of ‘temporary structures’ and ‘temporary states of weakness or instability’ and applies to such situations.