Italian prosecutors are opening an investigation into the Genoa bridge collapse, as questions swirled over what caused the structure to crumble.
At least 38 people died when a 650-foot portion of the Morandi motorway bridge in northern Italy disintegrated on Tuesday.
The 51-year-old structure, designed by celebrated Italian engineer Riccardo Morandi, has been beset with problems since its construction in the 1960s, leading to expensive maintenance and drawing fierce criticism from engineering experts.
Possible mafia connections have been raised.
Dave Parker, Technical Editor Emeritus of New Civil Engineer told Radio 4's Today programme that the quality of the materials could have been affected by mafia involvement in the construction industry.
"According to urban myths, the mafia had a very big finger in the pie of the concrete industry back then, charging full price and putting less cement in," he said.
Genoa motorway bridge collapses
Concerns have also been raised about the integrity of other structures built following the Second World War, with one engineering body saying tens of thousands of bridges and viaducts in Italy could be at risk.
Giuseppe Conte, the Prime Minister, said "all infrastructure" across the country needed to be double-checked. "We must not allow another tragedy like this to happen again," he added.
Danilo Toninelli, the Transport Minister, said the collapse was "unacceptable" and that if negligence played a role "whoever made a mistake must pay."
Built between 1963 and 1967, the bridge had a maximum span of 718 feet, a total length of 0.7 miles, and concrete piers - vertical structures buttressing the arches of a bridge - that reach 295 feet in height.
'Structural doubts' over design
The technology of pre-stressed reinforced concrete used in the construction was the hallmark of its designer, Mr Morandi, who died in 1989.
Dubbed patent "Morandi M5", he had used the technology for other works, including a wing of the Verona Arena in 1953.
This technique also characterises another, even longer and just as problematic Morandi bridge: the 5.4 mile long General Rafael Urdaneta Bridge that spans the bay of Maracaibo, Venezuela, and was completed in 1962. It partially collapsed in 1964 after being hit by an oil tanker and was rebuilt.
The Morandi bridge in Genoa had always presented "structural doubts", according to an article published by specialist engineering website "Ingegneri.info", which called it "a tragedy waiting to happen".
Antonio Brencich, a professor of reinforced concrete construction at the University of Genoa, echoed those concerns.
"It was affected by extremely serious corrosion problems linked to the technology that was used (in construction). Morandi wanted to use a technology that he had patented that was no longer used afterwards and that showed itself to be a failure," Professor Brencich told Radio Capitale.
Professor Brencich has long been a critic of the bridge. Two years ago, he told "Ingegneri.info" that the bridge's construction went over budget and poor calculations over concrete viscosity led to an uneven road surface which wasn’t fully corrected until the 1980s.
Safety work had been commissioned
Mr Toninelli said the company that has the concession to operate that section of highway said its maintenance on the bridge was up to date and no work was being done at the time of the collapse. But he added that they were about to launch a 20 million euro (£17.8 million) bidding process for significant safety work on the bridge.
"There has not been sufficient maintenance and checks, and safety work for many bridges and viaducts and bridges in Italy constructed - almost all - during the 1960s," he said.
The tender provided for a strengthening of the bridge’s pier cables, including those of pier nine, the one that collapsed on Tuesday.
Notwithstanding the importance of a road that sees 25 million vehicles pass along it every year, the demolition of the bridge was being studied as far back as 2009.
Bridges such as the Morandi viaduct should have a lifespan of at least a century, "Ingegneri.info" reported, but the structure had been the subject of major maintenance work in the years after its completion, in particular to repair cracks and combat degradation of the concrete.
In the early 2000s the suspension cables put in place in the 1980s and 1990s were replaced.
"Fifty years ago, we had unlimited confidence in reinforced concrete, we thought it was eternal, but now we know that it only lasted a few decades," Diego Zoppi, former president of the Genoa branch of the order of architects, told reporters on Tuesday.
Mr Zoppi warned that it was impossible to say similar tragedies would not happen again without serious work on infrastructure built after the Second World War.
"The Italy built in the 1950s and 1960s is in urgent need of renovation. The risk of collapses is underestimated, the works built at that time are coming to an age when they are at risk."
'Tens of thousands need to be replaced'
The Italian CNR civil engineering society said structures as old as the Morandi Bridge had exceeded their lifespan. It called for a "Marshall Plan" to repair or replace tens of thousands of bridges and viaducts built in the 1950s and 1960s.
Updating and reinforcing the bridges would be more expensive than destroying and rebuilding them with technology that could last a century.
They cited previous accidents: a bridge that fell in April 2017 in the northern province of Cuneo, crushing a carabinieri police car after the officers and driver had barely managed to get away in time; and an overpass that in the northern city of Lecco that collapsed under exceptional weight, crushing a car and killing the driver.
Experts also said it was possible the thunderstorm could have contributed to the collapse after witnesses said it was struck by lightning shortly before it crumbled.
"As this reinforced and pre-stressed concrete bridge has been there for 50 years it is possible that corrosion of tendons or reinforcement may be a contributory factor," said Ian Firth, former president of The Institution of Structural Engineers. He called the bridge "an unusual design."
"The fact that there was reported to be a storm at the time may or may not be particularly relevant.”
Mehdi Kashani, an associate professor in structural mechanics at the University of Southampton, said maintenance issues and pressure from "dynamic loads," such as traffic and wind, could have resulted in "fatigue damage in bridge components."