CROSS Safety Report
Spalling concrete falling from motorway bridge
This report is over 2 years old
Overview
A major infrastructure owner reports on how an incident occurred at a motorway overbridge resulting in a piece of spalling concrete falling onto the carriageway and striking a vehicle.
They share what they feel were the contributory factors and the lessons that can be learned from it.
Key Learning Outcomes
For asset owners and managers:
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Regular inspections and maintenance can help keep a structure safe and detect any obvious maintenance issues
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Principal bridge inspections should be undertaken strictly in accordance with current standards and with particular emphasis on a close examination of the elements of the structure
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Concrete repairs should be undertaken by a competent contractor in accordance with current good practice with all as-built details recorded
Full Report
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The Full Report below has been submitted to CROSS and describes the reporter’s experience. The text has been edited for clarity and to ensure anonymity and confidentiality by removing any identifiable details. If you would like to know more about our secure reporting process or submit a report yourself, please visit the reporting to CROSS-UK page.
It has been reported that an incident occurred at a motorway overbridge resulting in a piece of spalling concrete falling onto the carriageway and striking a vehicle. This resulted in minor injuries to the driver. It is understood that the concrete which fell was no greater than 50 - 60mm in size. It had spalled from an area of previously repaired concrete on the cantilevered deck soffit located over the carriageway and resulted in closure of the motorway for three hours.
Risk mitigation plan established
During closure an initial special inspection of the structure was undertaken and other areas of potentially loose concrete were removed. Subsequently a full review of all the structures on both carriageways of this section of the motorway was carried out. A risk mitigation plan established based on a programme of special inspections to identify areas of concrete with potential to spall.
This was developed into a programme of ongoing inspections and concrete removal to manage the risk of further such incidents. Risks will be managed further when planned substantial concrete repair works are undertaken over the next two years as part of an upgrade scheme.
Several contributory factors identified
The following have been identified as contributory to the concrete spalling incident:
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Corroding reinforcement as a likely consequence of poor design detailing and quality of construction (reinforcement with low concrete cover in close proximity to a drip detail and relating to the date of original construction in 1962)
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The poor quality of the concrete repair carried out around 2008 (likely poor detailing with feathered edges to the repair, poor adhesion combined with repair material not being anchored around adjacent reinforcement)
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In addition, there was a lack of as-built information relating to the repair
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A recent principal bridge inspection had not included a close examination of the elements of the structure above the relevant lane
The following lessons learned have been identified:
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The need for a good quality of design and construction to provide a safe and durable structure
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The need for quality concrete repairs to be undertaken in accordance with current good practice and as-built details recorded
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The need to undertake principal bridge inspections strictly in accordance with current standards and with particular emphasis on a close examination of the elements of the structure
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Expert Panel Comments
Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.
This is an important report from a major infrastructure owner and is most welcome as the lessons learned from a potentially serious incident are being shared. It highlights the importance of design in its widest sense and not just numerical code compliance.
It is also a reminder that all structures deteriorate in use and inspections are required to look at how degradation is progressing and to be alert for the likely implications. However, the remedial works were carried out only seven years ago which is not a long life span for safety critical repairs.