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‘Scandalous’ failure to replace damaged Menai Bridge hangers 30 years ago put structure at risk

Engineers’ report originally recommended replacement in 1991
By Thomas Johnson

Engineers recommended that hangers on the Menai Bridge be replaced because they were at risk from brittle failure more than 30 years before safety concerns led to the closure of the structure last autumn.

The need for ongoing repairs was identified in 1991 but was not acted on

The 197-year-old suspension bridge connects mainland Wales and the Isle of Anglesey and was originally designed by Thomas Telford. It was revealed to be at “credible risk of an unzipping failure of the bridge deck [which] may have led to catastrophic loss of life” in a technical briefing document shared with NCE in February (NCE, March). The document was produced by consultant Cowi for Menai Bridge operator UK Highways A55.

The bridge was closed to all motorised traffic on 21 October 2022. UK Highways A55 allowed the structure to reopen with a 7.5t weight limit in February following emergency repairs by Spencer Group.

The structure consists of two 52.7m high masonry towers which support two sets of steel chains across the 176.7m main span and pairs of steel chains supporting the two approaches. The approaches are masonry arch viaducts with four spans on the Anglesey side and three spans at the Bangor Mainland end.

The deck of the main span is suspended from the chains via vertical spiral strand hangers. On the side spans, vertical hangers connect the chains to the masonry viaducts to control the profile of the chain and limit the horizontal movement of the roller saddles at the tower tops.

The Cowi document states that the issue which led to the closure centred on an “unacceptable risk of brittle failure” in hanger sockets which were installed during a major upgrade between 1938 and 1941. The document shows that 40 hangers were replaced between 1989-1991 but the remaining 202 were not.

It has now been revealed that the capacity of the hangers which were not replaced during the 1989 to 1991 work was questioned after structural inspection carried out by consultant Sir Alexander Gibb & Partners in 1991. A recommendation that the remaining hangers be replaced was made, but appears to have been ignored. Since the 1991 report no further hangers have been replaced.

Isle of Anglesey County Council chief executive Dylan Williams said: “We are extremely disappointed and concerned.

“Had there been an appropriate maintenance programme in place the recent bridge closure and resulting community impacts may well have been avoided.

“Robust and resilient connectivity between Anglesey and the mainland is essential.

“We remain hopeful that the outcome of the North Wales Transport Review, led by Lord Burns, will influence the Welsh Government to take appropriate and immediate action.”

Rhun ap Iorwerth, who is Plaid Cymru deputy leader and a Senedd for Anglesey member, said: “If 40 hangers were replaced around 1990 and there was a recommendation to replace the rest, then there should have been a programme in place to change all the hangers over time.

“It’s scandalous that successive governments didn’t make sure that the long-term wellbeing of the bridge was assured.

“The way in which the bridge had to be closed with no notice last October was hugely problematic – we shouldn’t have been in a position where a decision to close it needed to be made that quickly.”

Despite the revelation that repairs should have been undertaken in the last three decades, work is now underway to replace the hangers.

In the coming months, 168 will be removed using a custom-designed de-tensioning rig and then replaced with new hangers. A timeframe for completing the work has yet to be announced.

Once the new hangers are installed, the Menai Suspension Bridge will can reopen without restrictions.

Hanger replacement is likely to be tied in with other upgrades to the bridge to avoid future closures.