Experts say it is too early to know what caused the Morandi bridge in north-west Italy to collapse

Experts described the bridge that collapsed in northern Italy leaving at least 20 people dead on Tuesday as “very unusual” and said that although it was too early to say what might have caused the tragedy, ongoing repairs or recent storms may have played a part.

Ian Firth, a former president of the Institution of Structural Engineers and a specialist in bridges, said the 1km-long structure was supported by two A-frame towers using concrete-encased stay cables, and had been built in the 1960s.

“As this reinforced and prestressed concrete bridge has been there for 50 years, it is possible that corrosion of tendons or reinforcement may be a contributory factor,” he said. “In addition, ongoing work on the bridge may or may not be partly responsible for the collapse.” He added that the bridge, created by the civil engineer Riccardo Morandi, was a “very unusual design”.

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The bridge has undergone frequent repairs since the 1970s and there has reportedly been some concern about its ability to withstand the volume of traffic that used it.

The flyover of the A10 motorway, named after the architect who designed it, spanned railway lines, buildings and the Polcevera stream about 45 metres (145ft) below.

Tim Ibell, a professor of civil engineering at the University of Bath, described the collapse as a tragedy and said skilled structural engineers would “look for tell-tale signs of initiation of failure”.

He added that such incidents were thankfully very rare. “It is of no comfort to today’s victims and their families, but the reality is that the beautiful, enormous bridge structures we see all over the world stand safely due to the extraordinary abilities of structural engineers.”

Prof Gordon Masterton, the chair of future infrastructure at the University of Edinburgh’s school of engineering, said there needed to be a “forensic and thorough” investigation to get to the root cause.

“There are several potential triggers for what appears to have happened and until more evidence is obtained from the debris, the eyewitness accounts and the videos, it is unproductive and disrespectful to speculate as to whether one is more likely than the others,” he said.

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Dr Maria Rosaria Marsico, a senior lecturer in structural engineering at the University of Exeter, also emphasised that judgements must be informed by scientific evidence. She described the bridge as “a beautiful expression of engineering design”, and noted that the prestressed concrete stays were “a common feature of bridges designed by Morandi in the sixties”.

“The viaduct was subject to maintenance work since it was built and in the 90s a complex intervention of repair was carried out involving the installation of conventional steel tendons,” she added.

Though experts were responsibly cautious about possible causes in this instance, it emerged that concerns have been raised about the bridge in the past. In 2016, Antonio Brencich, a professor specialising in reinforced concrete construction at the University of Genoa, called the span “a failure of engineering”.

“That bridge is wrong. Sooner or later it will have to be replaced,” he said. “I do not know when. But there will be a time when the cost of maintenance will be higher than a replacement,” he told the Italian media organisation Primocanale.

Officials have stated that the bridge was properly maintained.