HSE Press Release E005:04 - 13 January 2003
Following the partial collapse of a Wolverhampton car park in 1997, the Health and Safety Executive (HSE) has published research into the cause of the collapse.
On the night of 20 March 1997 a 120 tonne section of the top deck at the Pipers Row multi storey car park collapsed. Although open, the car park was unoccupied and no-one was injured.
Pipers Row car park was a flat slab structure, designed and built in 1964/65 using a technique called 'Lift Slab'. It was believed to be the first 'Lift Slab' structure to have failed in service. The research was commissioned following concerns about car parks built using the 'Lift Slab' technique and about the safety of other flat slab structures subject to aggressive environments.
The research found that if properly maintained, Pipers Row car park should have had a reasonable margin of strength in relation to the actual loads imposed in use. However, deterioration of the concrete over and around the column/slab zone led to punching shear failure of the concrete slab. The mechanical column/slab connection unique to the 'Lift Slab' method of construction did not fail.
The concrete deterioration resulted from localised breakdown of the overlying waterproofing membrane. This allowed water access to areas of poor quality concrete in the upper part of the slab leading to frost damage and a loss of strength.
The research also found that assessment of structural integrity of this form of 'Lift Slab' structure requires cautious engineering judgement. Interpretation of the unusual characteristics of the column/slab connection using current design codes can result
in an under estimation of load acting on the structure, and an over estimation of strength. To assist those who have to assess the structural integrity of these structures the report identifies potential pitfalls and makes further recommendations.
The report also highlights concerns about the generalised robustness requirements in current design codes. For some types of reinforced concrete structures, including flat slabs without adequate provision of bottom reinforcement over the columns, there may be a risk of progressive collapse following punching shear failure.
One of the main lessons from the research to help prevent similar collapses is that owners of car park structures need to have robust procedures in place. The employment of people with appropriate levels of competence is also significant, to ensure that these structures are properly inspected, maintained and - where necessary - repaired.
A copy of the report is published on HSE's web site: http:/www.hse.gov.uk/research/misc/pipersrow.htm
Information arising from this investigation has been made available for the preparation of the following documents:
All enquiries from journalists should be directed to the HSE Press Office
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