CROSS Safety Report
Progressive collapse of mill building
This report is over 2 years old
Nearby families were evacuated after part of a four-storey former mill building collapsed adjacent to their homes.
Key Learning Outcomes
For civil and structural design engineers:
Be aware that buildings that have performed adequately during their life may hide vulnerable details which make their behaviour unpredictable during extreme events
If working on older multi-storey buildings be aware of the potential for sudden progressive collapse and routinely raise the risks to contractors and the wider project team
Be aware that Part A of the building regulations, and particularly the section on disproportionate collapse would apply in the case of change of use
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Nearby families were evacuated after part of a four-storey former mill building collapsed adjacent to their homes (Figure 1). Residents reported hearing a sound like a heavy goods train as the building fell. The mill was used for storage and was about to be converted into residential apartments. The reporter said that the construction was typical of 19th century mills with brickwork interior walls, cast iron columns and filler joist floors. It is thought that the sudden collapse was initiated by the failure of one of the columns.
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Expert Panel Comments
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This is a classic example of progressive collapse following the removal of a single element. It happened suddenly and apparently without warning and it was fortunate that nobody was inside and the debris did not hit the nearby houses.
Buildings such as this were not designed with robustness in mind and there was no structural continuity and little in the way of bracing apart from façade walls. They were constructed, not always very well, for specific industrial purposes and are now used for a variety of functions including conversion into residences.
Buildings such as this were not designed with robustness in mind and there was no structural continuity and little in the way of bracing apart from façade walls
Robustness and progressive collapse
Part A of the building regulations, and particularly the section on disproportionate collapse would apply in the case of change of use. The Institution of Structural Engineers is preparing a report on ‘Robustness and progressive collapse’, and CROSS are concerned that the concepts are not well understood.
Buildings that have performed adequately during their life may hide vulnerable details which make their behaviour unpredictable when subjected to ‘Events’. Those involved with damaged buildings and those undergoing alteration should consider this. Developers, designers and contractors, must be aware of the potential for catastrophic progressive collapse of some older multi-storey buildings.
Useful references when examining or altering such structures include:
Appraisal of Existing Iron and Steel Structures -1997 SCI P138
Historical Structural Steelwork Handbook - BCSA 1984
Structural Renovation of traditional buildings - CIRIA 111 1994
Appraisal of existing structures - Institution of Structural Engineers 1996