Engineering Experts Knew Italian Bridge Had Corrosion Problems Before It Collapsed, Report Says (apnews.com)

McGruber shares a report: Engineering experts determined in February that corrosion of the metal cables supporting the Genoa highway bridge had reduced the bridge's strength by 20 percent -- a finding that came months before it collapsed last week, Italian media reported Monday. Despite the findings, newsmagazine Espresso wrote that "neither the ministry, nor the highway company, ever considered it necessary to limit traffic, divert heavy trucks, reduce the roadway from two to one lanes or reduce the speed" of vehicles on the key artery for the northern port city. A large section of the Morandi Bridge collapsed Aug. 14 during a heavy downpour, killing 43 people and forcing the evacuation of more than 600 people living in apartment buildings beneath another section of the bridge.

Comments

The other mistake

[SuperKendall]

If corrosion weekend the cables by 20% of so, it seems like the original design didn't leave nearly enough margin for error!

I imagine they were not as concerned with 20% weakening thinking they had much more leeway.

Re:The other mistake

[fredgiblet]

Read the wiki article on the bridge. They've been fighting it's design for it's entire life and were even starting to prepare a replacement.

Re:The other mistake

[Freischutz]

If corrosion weekend the cables by 20% of so, it seems like the original design didn't leave nearly enough margin for error!

I imagine they were not as concerned with 20% weakening thinking they had much more leeway.

It’s not just that, the bridge was hopelessly overloaded by traffic. There is a longstanding bypass project which has been fiercely opposed by the Five Star Movement for years. The Five Star Movement’s leaders, who now run Italy, actually cracked jokes about warnings that this bridge might collapse at regular intervals since the first warnings in 2012 or 2013. They are now trying to blame the EU (which gave them money for infrastructure sanitation) for the whole ugly mess.

Re:The other mistake

[bobbied]

Time to accelerate those replacement plans I guess.

Re:The other mistake

[Immerman]

It's been a lot of years since engineering school, but I seem to recall the recommended safety margins for most things were 100%-500%, so yes, a 20% weakening causing collapse would be a symptom of serious under-engineering.

However, Wikipedia says this bridge is 51 years old, and that engineers have been expressing concern over its safety since the early 90s, with numerous other static and dynamic weaknesses being uncovered over the years, due to both degredation, and weakness in available computer modeling in the 60s.

Apparently traffic has quadrupled since it was built as well, so it's probably been under a lot more stress than it was really designed for. And to top it all off, eye witnesses say it was struck by lightning just before the collapse - and I would imagine conducting that kind of amperage (~30kA typical) could heat a cable enough to weaken it considerably. You'd think good engineering would factor in lightning strikes on a tall bridge like this, and they probably did, but it was probably just one stress too many on an old bridge.

Re:The other mistake

[Thelasko]

AvE posted a great video on this bridge. The designer of the bridge didn't like adding extra reinforcing. This was probably for aesthetics. This made maintenance of the bridge difficult as structural components couldn't be repaired while the bridge was in service.

Re:The other mistake

[iMadeGhostzilla]

I've read about an engineering principle they used in England in the Middle Ages to make bridges safer: bridge constructors were required to sleep for two weeks under the bridge after it was constructed. With their families.

Re:The other mistake

[mikeiver1]

Though I generally agree with your assessment of the issues there are a few I can take an alternate view of.

First is that the strike to the cables would not have lasted long enough to cause heat induced weakening of them, But... The high current upon entering the the wet concrete could have caused the water to flash over to steam and maybe induce cracking in the structure.

Second is the rebar embedded in the concrete supports has definitely corroded leading to weakened bonding and compromised structure internally. All concrete structures suffer this issue over time. Some deal with it by using epoxy coated rebar, some use composite rebar, and others use stainless steel to stave off this inevitable failure.

Third is that the bridge was carrying four times the original traffic it was designed for and at speeds likely far in excess of those thought prudent at the time of design and build. This again added to the stressed induced on the structure and I would submit accelerated its failure.

It is very likely that there were one or more engineers blowing the caution horn for some time now. It is also likely that they were flatly ignored, removed from the job, or sent elsewhere to silence them. Nice to see that the higher ups that lost their jobs at Morton Thiokol found new places to work and ways to kill others.

Re:The other mistake

[Anonymous Coward]

It's been a lot of years since engineering school, but I seem to recall the recommended safety margins for most things were 100%-500%, so yes, a 20% weakening causing collapse would be a symptom of serious under-engineering.

IAAME (I Am An Mechanical Engineer). For civil engineering projects, a safety factor of 3 to 4 would be normal and more than likely would be documented

However, Wikipedia says this bridge is 51 years old, and that engineers have been expressing concern over its safety since the early 90s, with numerous other static and dynamic weaknesses being uncovered over the years, due to both degradation, and weakness in available computer modeling in the 60s.

Years after it was built, the DESIGNER of the bridge expressed concerns about its safety. Because of pollutants in the air, the weather pattern around the bridge, and the unique design of the bridge, he specifically said that corrosion on its parts was greater than he had observed in other bridges of this same design. HE warned that they really needed to watch this bridge closely for corrosion problems. And because of the lack of computer modeling, that normally causes good engineers (which I believe the bridge designer to have been) to over specify the safety factor. I think this is a clear case of the authorities not doing maintenance on a bridge that clearly needed extra maintenance and it just caught up to them. Gordon

Re:The other mistake

[MightyYar]

Yeah, the design's use of prestressed concrete cables with zero redundancy is borderline baffling. It's a visually stunning design (especially given the era), but come on! I've also never seen suspension bridge (ok, technically cable-stayed bridge) where they span two suspended portions with nothing but a more-or-less standard concrete segment. Maybe this was common at one time, but most of the recent ones seem to overlap the stays.

Re:The other mistake

[Solandri]

Engineering safety margins (you calculate the maximum stresses, figure out how string the structure would need to be to withstand it, then build it x times stronger) are typically:

• Missiles and experimental aircraft - 1.1 to 1.25x
• Aircraft carrying passengers - 1.5x
• Boats - 2.0 to 2.5x
• Cars - 3x
• Static structures like buildings - 10x

These are general rule of thumb. Specific parts may have higher or lower safety margins depending on how predictable or unpreditable the stresses will be. I would imagine bridges fall under the same category as buildings. Although suspension bridges have always been a bit of a balancing act between weight and strength. Some quick googling suggests the safety margin for the suspension elements is typically 2.0 to 4.0.

Also, if you're using metal, corrosion is inevitable. Even stainless steel will corrode (it called stainless, not stainnever). You need to adhere to a strict regimen of inspecting the metal parts for corrosion and protecting it painting, lubricating, replacing). It sounds like this bridge used pre-stressed concrete stays instead of metal wire stays. Concrete is extremely strong in compression, but weak in tension. If you pre-compress it with metal rebar, that can make it usable in tensile applications where you normally wouldn't think it would work. Basically, the rebar is pulling the concrete in compression more than the load is pulling it in tension, so the concrete remains in net compression and doesn't fall apart. But that balancing act between tension and compression is highly dependent on the metal rebar suffering minimal corrosion and retaining its strength.

Tempered glass is another example of how pre-stressing a fragile material to keep it under compression can make it stronger (strong enough to survive being shot by a bullet).

Re:The other mistake

[fph il quozientatore]

They took it offline now (surprise!), but it's still available in the Internet Archive. Google-translated version: https://translate.google.com/t... "We are then told, in turn, the tale of the imminent collapse of the Morandi Bridge"

Re:The other mistake

[pilaftank]

It was designed by Calatrava

The Ponte Morandi bears the name of its designer:
Riccardo Morandi

"Bridges by Morandi have proved to require extensive maintenance and repairs over the years to pass bridge safety inspections. The third span of Ponte Morandi collapsed in Genoa, on 14 August 2018, causing 43 fatalities."

Re:The other mistake

[Hoi Polloi]

I think it was already accelerated at about 9.8 m/s^2

Re:The other mistake

[bobbied]

I think it was already accelerated at about 9.8 m/s^2

Given the gravity of the situation, I believe you are right.

Re:The other mistake

[arglebargle_xiv]

The Full Calatrava gives all the gory details. To his credit, it does list one single project that didn't go over budget or fail. However, although the Ponte Morandi is worthy of the likes of Calatrava or Frank Lloyd Wright, just the name "Ponte Morandi" tells you it was a Riccardo Morandi design, and he's no Calatrava. He's also been safely dead for several decades, so he can't be sued.

Re:That makes sense

[jiriw]

Unless the bridge was already built less strong than specified and the extra 20% was just the tipping point, or there were other factors involved that made the bridge collapse...
Another example: In Italy, many things are built outside specification due to mafia involvement... because taking shortcuts made it possible to pocket construction money. I'm not saying it happened here but it's just to give you another possibly 'far fetched' explanation.

You shouldn't put the blame on someone specific (also named: scapegoating) unless research into this catastrophe has a chance to finish and hopefully will find out what really happened... And lets pray that can be done without politics involved because this collapse already seems to be a highly laden subject in that regard.

Re:That makes sense

[lgw]

If the bridge was only over-engineered by 20%, then it would be a disaster to keep using it.

It seems like the engineers have been opposed to this bridge design from the beginning, pointing out the impending disaster since 2012, and advising limiting traffic and building an alternate route. But good luck getting politicians in a democracy to spend money on infrastructure (even when given money by the EU specifically for infrastructure).

Re:That makes sense

[Immerman]

It was an old bridge (circa '67), with lots of other problems too - including the fact that traffic had quadrupled since it was designed. Engineers have been expressing concerns since the 90s. And witnesses say it was also struck by lightning just before collapsing. So it wasn't a simple matter of just corrosion-weakened cables.

But yes, if it was only over-engineered by 20% it would have collapsed decades ago.

Bridge engineers always consider overload

[SuperKendall]

Itâ(TM)s not just that, the bridge was hopelessly overloaded by traffic.

Have you ever driven in New York City? Every bridge is totally full of traffic nearly 24x7, during rush hour basically parked (it took me an hour once to cross George Washington bridge leaving NYC near rush hour). That happens every day, including in driving rainstorms... bridges are usually built assuming the bridge is packed with trucks, during the worst storm imaginable (including many feet of snow, far worse than rain), then use safety margins well beyond that. It seems the designers of this bridge cut some corners.

Re:Bridge engineers always consider overload

[Freischutz]

Itâ(TM)s not just that, the bridge was hopelessly overloaded by traffic.

Have you ever driven in New York City? Every bridge is totally full of traffic nearly 24x7, during rush hour basically parked (it took me an hour once to cross George Washington bridge leaving NYC near rush hour). That happens every day, including in driving rainstorms... bridges are usually built assuming the bridge is packed with trucks, during the worst storm imaginable (including many feet of snow, far worse than rain), then use safety margins well beyond that. It seems the designers of this bridge cut some corners.

I’ve driven in all kinds of places. However, the real question is: Have you ever observed the dysfunctional cocktail of corruption, populism and incompetence otherwise known as Italian politics at work? In this case you have a steadily deteriorating bridge whose load carrying capacity is rapidly decreasing, that may not have been built to specs in the first place due to corruption and that was being subjected to traffic loads and thereby vibrations that its decayed structure could not handle. And the whole time there is a political cat fight going on with a bunch of populists wingnuts who are blocking the replacement bypass project, staging protests against any repair work and ridiculing anybody who spoke out about the danger of the situation. The bottom line is that this bridge should have been replaced and decommissioned at least ten years ago.

Re:That makes sense

[lgw]

They both failed at their jobs resulting in loss of life, by the sound of it.

If by "failed" you mean "consistently warned about the impending disaster for the past 6 year, while politicians openly mocked the warnings", then sure.

And maybe both will see jail time

Probably so. It's not like the politicians who blocked funding of an alternate route are going to let any consequences affect themselves.

re: cutting corners

[King_TJ]

One article I read said there was a good likelihood the bridge was constructed using less concrete than specified, because the mafia was heavily involved in bidding for these projects at the time. One of their favorite ways to win low bids for construction was skimping on the concrete used.

I-35w bridge collapse was USA's wake-up-call!

[Joe_Dragon]

I-35w bridge collapse was USA's wake-up-call!

Corrosion problems on Forth Road Bridge in Scotlan

[Pop69]

When they identified corrosion problems with the main cables on this bridge, they installed dehumidifiers for the cables. They also built a replacement bridge and now use the older bridge as a public transport route, a traffic level it can easily cope with. Perhaps this should have been done with this bridge too ?

The problem was known much earlier

[mi]

The bridge's sorry state was known years ago. A certain political party used the "environmentalist" demagoguery to keep the status quo.

And now the same people are blaming the company that built and maintained the structure:

Transport Minister Danilo Toninelli, a member of the governing Five Star Movement (M5S), called for the immediate resignation of the company's top management Wednesday.

"First of all the top executives of Autostrade have to resign," he said in a message on Facebook. "If they can't manage the motorways, then the state will do it."

Because the government is so good at everything...