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Exclusive | Collapsed Italy bridge investigators find corrosion on main stay cables

Italy collapsed bridge

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. 

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Readers' comments (4)

  • Between each of the cable stayed spans there was a short suspended span which appears to be half jointed. There was a similar short suspended span between the collapsed cable stayed span and the approach viaduct. In the video across the rooftop (in heavy rain) that shows the mast collapsing it appears that this suspended span had already dropped before the mast collapsed. It could have been a half joint failure that initiated a progressive collapse.

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  • It now seems quite possible that the principal reason behind this catastrophic failure was the designer's decision, 50 years ago, to use steel tie bars clad in concrete as the bridge's main tension members.

    This was essentially a cable stayed bridge design in which the steel tension cables were wrapped in concrete instead of paint (or a similar corrosion resisting medium). The concrete wrapping provided no structural benefit to the bridge and instead went on to prevent the ready inspection and maintenance of the main steel strength members it enclosed.

    Concrete is excellent for compressive loads but useless in tension. Steel is excellent for tensile and compressive loads but needs a protective coating to prevent corrosion.

    Also it seems that there was also no redundancy in the structure - a single member failure could lead to total collapse.

    These are significant design failings in my view.

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  • @Donald Drysdale : I agree with your appreciation. Having read some pages of books written in the 1960's on Riccardo Morandi's bridges, it is quite obvious that many persons of that era were praising too much Mr Morandi's designs and skill.

    For me, it is a clear case of what I call "The Pygmalion Effect": when a creator of a given work becomes so enamored of his/her work that he/she ends up believing that his/her solution is not only the best, but the only way to go.

    Back in the 50's and 60's, too many engineers were dazzled with the then new possibilities of reinforced concrete construction. Morandi probably became obsessed with the intensive substitution of steel with the much less expensive concrete. One thing is now clear: Morandi could be brilliant,but his obsession with the (ab)use of concrete over steel carried him and their companions to propose what now seems a very bad idea: the use of bridge stays made of prestressed concrete instead of using steel tendons WITHOUT any concrete. I'm no Civil Engineer (actually I'm a Chemical Eng.) but I've known since school days that a long slender member that works in compression is limited by buckling. Now, Morandi obsession with prestressed concrete for the stays of his bridges was a very bad decision, because the stays are very long and slender, so much that their prestressing HAD TO BE VERY LOW (unless risking to bucke them with the prestressing!), which opens the real possibility of cyclic stresses to cause concrete micro cracks that allow the humidity to penetrate and corrode the steel cables, which are not accesible for inspection as they are buried inside the concrete. Your comment on the amazing lack of redundancy is spot on. It appears that Morandi was so convinced of his skill that he disdained the use of several stays instead of his approach: just four stays per tower. a single stay failure DOES bring the entire tower down. In addition to the designer (Morandi), those who praised him and became too enthusiastic about his designs are equally guilty of this disaster: read the many books published in the 60's that praise the designer too much and you can see how everybody contributed to his designs being admired so much that NOBODY felt the need to revise the concept. As of today (2018), at least three of Morandis bridges have failed: the Wadi El Kuf bridge in Libya has been closed since 26 October 2017 when the Security Directorate of the Green Mountain region in east Libya called on the security services to close down the bridge, following recent inspections that identified potential fractures. Surprinsingly, the war-torn Libyans were much more careful than the Italians!, the second Morandi's bridge in Venezuela also has its share of problems, and the third is the Genoa one where almost 40 people died because of the overconfidence of that famous designer, now deceased. All of those bridges are of the very same design: Prestressed concrete stays, too few stays (No redundancy), and all of them were (stupidly) judged as "Works of Art". So, in my humble opinion, you can add petulance to overconfidence in a bad from the start design. Finally, I will risk to forward a prediction: One of these days, one of the "marvellous" bridge designs of Santiago de Calatrava ( that are extremelly 'atractive' ) but absurd because those were designed to stretch the imagination, will come down, sooner or later. To design too fancy and Bizarre bridges is not only wasteful, but reliability suffers and failure mechanisms could be easily understimated. Bridges should NOT be artistic above being safe, reliable and functional.

    Unsuitable or offensive? Report this comment

  • @Donald Drysdale : I agree with your appreciation. Having read some pages of books written in the 1960's on Riccardo Morandi's bridges, it is quite obvious that many persons of that era were praising too much Mr Morandi's designs and skill.

    For me, it is a clear case of what I call "The Pygmalion Effect": when a creator of a given work becomes so enamored of his/her work that he/she ends up believing that his/her solution is not only the best, but the only way to go.

    Back in the 50's and 60's, too many engineers were dazzled with the then new possibilities of reinforced concrete construction. Morandi probably became obsessed with the intensive substitution of steel with the much less expensive concrete. One thing is now clear: Morandi could be brilliant,but his obsession with the (ab)use of concrete over steel carried him and their companions to propose what now seems a very bad idea: the use of bridge stays made of prestressed concrete instead of using steel tendons WITHOUT any concrete. I'm no Civil Engineer (actually I'm a Chemical Eng.) but I've known since school days that a long slender member that works in compression is limited by buckling. Now, Morandi obsession with prestressed concrete for the stays of his bridges was a very bad decision, because the stays are very long and slender, so much that their prestressing HAD TO BE VERY LOW (unless risking to bucke them with the prestressing!), which opens the real possibility of cyclic stresses to cause concrete micro cracks that allow the humidity to penetrate and corrode the steel cables, which are not accesible for inspection as they are buried inside the concrete. Your comment on the amazing lack of redundancy is spot on. It appears that Morandi was so convinced of his skill that he disdained the use of several stays instead of his approach: just four stays per tower. a single stay failure DOES bring the entire tower down. In addition to the designer (Morandi), those who praised him and became too enthusiastic about his designs are equally guilty of this disaster: read the many books published in the 60's that praise the designer too much and you can see how everybody contributed to his designs being admired so much that NOBODY felt the need to revise the concept. As of today (2018), at least three of Morandis bridges have failed: the Wadi El Kuf bridge in Libya has been closed since 26 October 2017 when the Security Directorate of the Green Mountain region in east Libya called on the security services to close down the bridge, following recent inspections that identified potential fractures. Surprinsingly, the war-torn Libyans were much more careful than the Italians!, the second Morandi's bridge in Venezuela also has its share of problems, and the third is the Genoa one where almost 40 people died because of the overconfidence of that famous designer, now deceased. All of those bridges are of the very same design: Prestressed concrete stays, too few stays (No redundancy), and all of them were (stupidly) judged as "Works of Art". So, in my humble opinion, you can add petulance to overconfidence in a bad from the start design. Finally, I will risk to forward a prediction: One of these days, one of the "marvellous" bridge designs of Santiago de Calatrava ( that are extremelly 'atractive' ) but absurd because those were designed to stretch the imagination, will come down, sooner or later. To design too fancy and Bizarre bridges is not only wasteful, but reliability suffers and failure mechanisms could be easily understimated. Bridges should NOT be artistic above being safe, reliable and functional.

    Unsuitable or offensive? Report this comment

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