- Video report by Science Editor Tom Clarke
Investigators are working to determine what caused the deadly collapse of the Morandi motorway bridge in Genoa.
Italy's Interior Minister Matteo Salvini, has said that those responsible would "pay dearly" for the tragedy that killed dozens, including a family of three and another family of four.
So why did a 260ft (80m) stretch of the A10 road suddenly crumble 150ft (45m) to the ground of Tuesday?
Genoa prosecutor Francesco Cozzi said that the investigation into the collapse is focusing on human causes, specifically the possibility of inadequate maintenance or a design flaw in the bridge’s construction.
He said: “I don’t know if there is responsibility. For sure it was not an accident.”
Asked if authorities had been given any warning that the bridge — a key link between two major roads, one headed toward neighbouring France and the other to Milan – could be dangerous, Mr Cozzi indicated that no serious safety concerns had reached his office before Tuesday.
Otherwise, “none of us would have driven over that highway 20 times a month as we do,” he said.
Engineering experts, noting that the bridge was 51 years old, said corrosion and weather could also have been factors in its collapse.
Others have noted that although considered innovative in its time for its use of concrete around its cables, the design of the 1967 bridge meant that no repairs could be done to the metal cables if needed.
The bridge had also long been due for an upgrade, especially since the structure saw more heavy traffic than its designers had envisioned.
One expert in construction from the University of Genoa, Antonio Brencich, had previously called the bridge “a failure of engineering”.
Mehdi Kashani, an associate professor in structural mechanics at the University of Southampton in the UK, said pressure from dynamic loads, such as heavy traffic or wind, could have resulted in “fatigue damage” in the bridge’s parts.
The Italian CNR civil engineering society has said that structures dating from when the Morandi Bridge was built had surpassed their lifespan.
It called for a “Marshall Plan” to repair or replace tens of thousands of Italian bridges and viaducts built in the 1950s and 1960s, adding that simply updating or reinforcing the bridges would be more expensive than destroying and rebuilding them with new technology.
Work to upgrade the bridge with a £17.8 million project had already been approved, with public bids for the work to be submitted by September.
According to local media, the improvement work involved two weight-bearing columns that support the bridge – including one that collapsed on Tuesday.
Meanwhile, Italian politicians are busy pointing fingers at possible culprits.
Italy’s deputy premier, Luigi Di Maio, blamed the bridge collapse on a lack of maintenance by the private company that operates many of the nation’s toll highways.
Speaking in Genoa, Mr Di Maio said he was looking at revoking highway concessions.
“Instead of investing money for maintenance, they divide the profits. And that is why the bridge falls,” Mr Di Maio said of the holding company that controls Autostrade Per Italia.
Mr Di Maio, who leads the anti-business 5-Star Movement party that is part of Italy’s coalition government, also blamed previous Italian governments of turning a blind eye to the health of the nation’s toll highways because of political contributions.
Autostrade controls 1,876 miles of major Italian roads.
Italy’s minister of transportation and infrastructure, Danilo Toninelli, also from the 5-star party, threatened in a Facebook post that the state, if necessary, would take direct control of the highways agency if it could not properly care for roads and bridges.
In 2013, some 5-Star MPs had questioned the wisdom of an ambitious and expensive infrastructure overhaul programme as possibly wasteful, according to reports, but a post about that on the Movement’s site was removed on Tuesday after the bridge’s collapse.
Within hours of the collapse, Mr Salvini was vowing not to let European Union spending strictures on Italy, which is laden with public debt, stop any effort to make the country’s infrastructure safe.