CROSS Safety Report
Multi-storey car parks demolished due to structural defects
This report is over 2 years old
A reporter shares their experience on two instances where their firm has prepared reports and carried out numerical assessments of city centre car parks that have led to the car parks being demolished.
Key Learning Outcomes
For car park owners and operators:
Regular inspections and maintenance can help keep a structure safe and help identify any obvious safety issues that may need to be addressed
The British Parking Association in its Master Plan recommends that: ‘Owners and operators set aside funds from income streams to finance periodic structural inspections and essential maintenance of car park structures’.
The planning portal from the Department of Communities and Local Government has a report ‘Enhancing the whole life structural performance of multi-storey car parks’ which provides guidance and advice
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This reporter has two instances where their firm has prepared reports and carried out numerical assessments of city centre car parks that have led to the car parks being demolished. One had precast concrete beams which had come to the end of their life. The other was constructed in the 1970s using insitu reinforced concrete and is particularly interesting.
The reporter first carried out an inspection of the structure in 2003 and noted that the underside of the reinforced concrete waffle beams were in poor condition at mid span. However, the assessment indicated reserves of strength around the columns where re-distribution of moments would allow deficiencies in sagging to be partially taken by hogging reinforcement. Based on the typical parking usage at the site it was deemed that there was sufficient capacity to allow the car park to remain open in the short term.
The second inspection in 2008 revealed changes that alarmed the inspectors. Although there was little deterioration at mid span, the concrete around the columns was now in poor condition with widespread de-lamination of the upper surface. Due either to time or excessive stress or both, the top reinforcement was corroding, and the spalling revealed that there had been numerous previous concrete repairs to the top of the deck during past decades.
The de-lamination largely remained hidden by the surfacing but could be detected using laborious tapping of the surface. Analysis confirmed that low condition factors around the columns had a drastic effect on the capacity of the deck in both bending and shear, and particularly in bending combined with shear. The car park was shut, and the decks were propped pending demolition which was subsequently completed, but as the multi storey car park was above a town centre shopping area there were major complications.
The reporter’s main concerns are:
These car parks were under the control of local authorities with good technical staff, who were proactive in monitoring deterioration in their car parks. This is probably relatively unusual.
The presence of old repairs to the upper surface of the deck slabs around the columns had remained undetected in at least two previous structural inspections. This is likely to be very common.
The significance of deterioration would normally be missed as it involved relatively minor, if widespread, corrosion and spalling to the upper surface of the deck around the columns. Even an experienced engineer would not generally appreciate the significance of this if viewed in isolation and as a single snap shot in time.
The Pipers Row collapse in 1997 (see reference below) showed that shear failure in car parks has been found to take place with little warning other than relatively minor cracking around the columns. The second example here had a more traditional form of reinforced concrete construction, but the significance of cracking and spalling described above was believed to be very high.
Expert Panel Comments
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Headline events such as the at Pipers Row car park collapse in the UK in 1997, a Montreal parking garage collapse in 2008 (see Canadian News report), and others show that severe, and sometimes fatal, failures occur in such structures.
MSCPs are unique structures in many ways as they are:
Subject to relatively severe weather conditions due to exposed structure, carbonation etc
Sensitive to waterproofing finish failure
Sensitive to expansion joint sealant failure
Subject to extremes of thermal loading akin to bridges but rarely detailed to the same standard as bridges
The typical pattern of deterioration is such that failure is likely to be indicated by spalling but may be sudden and brittle with little or no warning. Given the history, and the likely consequences of failure, there may be a case for making it a legal requirement to have regular inspections of these structures. In the absence of such requirements those involved should ensure that their concerns are expressed in clear terms to their clients, with the consequences (to individuals and organisations) of failing to act being outlined.
Given the history, and the likely consequences of failure, there may be a case for making it a legal requirement to have regular inspections of these structures.
It may be that some owners and operators tend to ignore current legislation (not to mention their own liabilities) on the basis that a collapse of a MSCP is a rare occurrence. This is true, but they may be unaware of how close inadequately inspected and maintained car parks can come to collapse. It has been found that insurers take the same view on the basis that claims for collapses are few and the risk is acceptable given the number of car parks that they insure.
Are lack of funds compromising safety
From work carried out to date by the British Parking Association (BPA) it would seem that the most managers would like to maintain their facilities but are prevented from doing so by lack of funds. The BPA in its Master Plan therefore recommends that: ‘Owners and operators set aside funds from income streams to finance periodic structural inspections and essential maintenance of car park structures’.
Local authorities are non-profit making and any surplus of income from parking may sometimes go to support other services. It would, according to BPA, therefore be a major step forward to have legislation in place to provide an allocation of funds for proper inspection and maintenance in accordance with current legislation. Local authorities, practices differ, and some carry out their responsibilities very thoroughly and have excellent MSCPs.
In the aftermath of the Montreal collapse a coroner called for tighter inspection rules after finding that a car park that collapsed and killed a man was badly built and maintained. She says the structure, built around 1970, was in a sorry state and had surpassed its useful life.
Guidance and publications
Designers should take account of the durability requirements of car parks and there are three helpful publications.
- The Institution of Civil Engineers report ‘Recommendations for the inspection, maintenance and management of car park structures’
- The Institution of Structural Engineers report ‘Design recommendations for multi-storey and underground car parks’
- The planning portal from the Department of Communities and Local Government has a report ‘Enhancing the whole life structural performance of multi-storey car parks’
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