Investigators examining the scene of the collapsed Polcevera Viaduct, more familiarly known as Morandi bridge, have found damage to the main stay cables on the collapsed section of the bridge, New Civil Engineer can reveal.
Sources close to the investigation told New Civil Engineer that when examining the main stay cables evidence of corrosion and damage had been found.
They suggested a failure of the cables – which were encased in concrete to protect them from the elements – may be behind the collapse.
“I have heard that video footage from the CCTV cameras on the bridge just before the collapse showed concrete being exploded off the main stay because of the violence of some of the cables snapping underneath,” one source said.
Thirty-eight people were killed last week when a 250m section of the bridge, including one of three 90m high towers collapsed during a heavy thunder storm.
Engineers have also suggested a potential cause for its collapse could be that the heavy rain washed ground from underneath the tower, undermining its foundations. The bridge’s foundations were undergoing strengthening works at the time of collapse, according to Italian highways operator Autostrade.
However, while the source close to the investigation said that nothing was being ruled out at this stage, he said that the foundations for the collapsed tower “appeared to be stable”.
Likewise, New Civil Engineer’s founding editor Sydney Lenssen – who visited the site during its construction in 1965 – believes that other factors are more likely to have caused the collapse.
“At first look it doesn’t look like a fault in the foundations,” Lenssen said. “It appears to me that the structure has fallen down from above. So it looks like the structure has collapsed around the foundations, rather than the foundations causing the collapse.
“I suspect that one of the supports from underneath has given away. That or the cables above have suffered from corrosion.”
Likewise former president of the Institution of Structural Engineers Ian Firth said that corrosion of the cables was a likely cause of collapse.
“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.”
The Italian government has now launched an investigation into Autostrade following the collapse, which claimed at least 38 lives.
Autostrade now has until the end of the month to produce a report detailing any works undertaken on the bridge to ensure its safety.
Like what you’ve read? To receive New Civil Engineer’s daily and weekly newsletters click here.