Bridge problem could have led to ‘loss of life’
THE problem which caused the sudden closure of the Menai Bridge last year could have led to “catastrophic loss of life”, engineers ruled at the time.
The bridge was closed to traffic in October after issues with the span hangers were detected during routine maintenance.
A technical briefing document shared with the New Civil Engineer magazine has now shed more light on what exactly led to the closure.
It states that the issue centred on an “unacceptable risk of brittle failure” in hanger sockets which were installed during a major upgrade of the bridge between 1938 and 1941.
The briefing document, based on analysis by engineering and architecture consultancy Cowi, said that, “were a given hanger to fail in a brittle manner [...] the impulse loading from this event had the potential to cause brittle fracture in adjacent hangers, leading to a progressive and disproportionate collapse of the bridge deck”.
It added: “Due to the inherently unpredictable nature of brittle fracture, it is extremely difficult to accurately determine the probability of such an event, but the analysis showed there was a credible risk of an unzipping failure of the bridge deck.
“Such an event may have led to catastrophic loss of life and was thus considered an unacceptably high consequence event that could have credibly occurred.”
The bridge reopened to traffic earlier this month. Emergency works – started in January – were completed in the four-week timeframe. The first phase of temporary mitigation has seen work to strengthen the historic bridge’s hangers.
The Welsh Government and UK
Highways A55 Ltd, alongside engineering firms Spencer Group and COWI, said they are continuing to “work closely” to develop a plan for longer-term remedial work to bring the Menai Bridge back to full capacity. This work is anticipated to start in late summer.