Bridges have lifespans and need constant maintenance.
One of my first tasks as an intern at the Army Corp Of Engineers was to create 6 inspection packets (copies of every part) of the cape cod canal bridge, which was being inspected.
I know the tappan-zee bridge was replaced because the old one was just too old (designed to last 50 years, it was replaced at over 60 years).
One of the reason I left the engineering profession is no one wants to pay for it so it gets "deferred". The US's bridges get a c+ according to the American Society Of Civil Engineers.
I'm also a little curious why the cables were wrapped in concrete. Steel cables are common on bridges. stability side to side? Concrete is not great in tension (steel is very good in tension). As the article indicates, it was potentially hiding some of the cable corrosion, making the situation worse.
Beside the (wrong) idea of protecting the cables from corrosion, the concrete, as you said, was there to improve stability.
It is pre-stressed concrete, it is working in compression against the cable tension. The idea is that as the load increases, instead of pulling directly on the cables, it just decompresses the concrete.
You can think of the cable as a spring, with the bridge suspended it. As you walk on the bridge, it bounces. To prevent the bouncing, you can put the spring under high tension into a rigid pipe, with the ends of the spring attached to the ends of the pipe. This way, as you walk on the bridge, the spring tension will stay constant, only the compression on the pipe will vary.
>> I'm also a little curious why the cables were wrapped in concrete. Exposed steel cables are common on bridges. stability side to side? Concrete is not great in tension (steel is very good in tension). As the article indicates, it was potentially hiding some of the cable corrosion, making the situation worse.
the concrete was meant to be a protective sheath to stop cable corrosion. poor materials engineering at the time sounds like the issue
>> He believed using the system would reduce the sway of the bridge. Structural engineers seemed to agree.
But Mr. Morandi also believed that the concrete coating would protect the steel cables inside from the wear and tear of the elements.
“Concrete structures seemed to be eternal,” Mr. Majowiecki said. “This was the mentality.”
In that hope, he added, Mr. Morandi was greatly mistaken.
The concrete of the day turned out to be highly vulnerable to degradation, worsened perhaps by salty air from the Mediterranean Sea and the harsh fumes from nearby factories.
Cracks in the concrete shell let water in, and the steel began corroding almost as soon as the bridge was opened for traffic in 1967. But unlike bare cables, any corrosion was hidden deep inside, making it hard to detect."
It's incredible how well documented and rich of information is the article. I'm Italian and I could not find in any Italian newspapers all the information that I needed! It makes me aware of how poor is the information in my country!
> a structural engineering professor at the Politecnico di Milano, Carmelo Gentile, found troubling signals of corrosion or other possible damage...he has performed his tests on some 300 bridges around the world
It would be very interesting to know what he had to say about the other 299 bridges. After all, you can find someone who will tell you you have a structural problem with the safest bridge. It's hard to tell if they are a crank, someone with a vested interest, someone seeking publicity for their new diagnostic method, or genuinely an expert who is giving you good advice. But if Professor Gentile mostly says the bridges are fine, but singled out this one as a danger - then it's really worth listening to his other recommendations.
Slightly off topic, but they way they changed the info graphic as you scrolled was _really_ cool! This is one of the rare cases where extra JavaScript makes sense - it really improves the experience.
By "cool" do you mean it helped you read the article? I'm curious because I had the exact opposite response, I actually quit reading the article at that point. I think it might work better on a small screen, but I was reading it on a full size monitor with the window maximized. It actually took more time to scroll to the next sentence than it took to read the sentence. I found it too annoying to concentrate on the content.
How does this entire article get written without a single mention that much of the road infrastructure here, bridge included, had been privatized and was being managed by the Atlantia corporation. The article actually seems to put the reader on the mistaken impression that Autostrade (former name of Atlantia) is some sort of media management company.
"Autostrade, which handles media queries on behalf of the subcontractor, Spea Engineering, declined to comment."
The technical specifics of the bridge collapse are interesting, but the privatization of multiple road systems should have in theory let the company be cognizant of the systemic issues of the design practices of various eras, but how was this missed? The company was managing the bridge since 1999, almost twenty years now. This is as much or more of an organizational question as well as a private vs public ownership question as it is a technical one.
> He warned the company that manages the bridge, Autostrade per l’Italia, or Highways for Italy, but he said that it never followed up on his recommendation to perform a fuller computer study and to outfit the bridge with permanent sensors.
> For reasons it has not fully explained, Autostrade, which took over management of the bridge in 1999, did not carry out the same operation on the supports of the other two towers — including the tower that collapsed.
> Autostrade won the concession to run nearly half of Italy’s highways from a cash-strapped Italian government, starting in 1999. After that, there were no major renovations of the Morandi bridge.
I'm honestly and sincerely wondering if you read the same article.
"Autostrade won the concession to run nearly half of Italy’s highways from a cash-strapped Italian government, starting in 1999. After that, there were no major renovations of the Morandi bridge."
> of the road infrastructure here, bridge included, had been privatized
That's not correct. They're not privately owned: they're a sort of lease (I can't quite translate "concessione") because the government is still technically the one who onws it.
And for those other HN readers, there's also a public-owned company that handles roads, Anas, which is not doing well with regards to maintenance (this just to put into perspective that's not just a public vs private thing).
> by using investigators’ descriptions of a central piece of evidence — video footage captured by a security camera.
Whenever I read about these incidents, with only one camera angle, I almost want to buy a camera and point it outwards from my apartment just in case I catch something like this happening in my city.
Not a civ engineer... But the way things cascaded and experienced a domino effect seems troubling. Contrast with the ‘89 SF quake caused one upper deck section of the then cantilevered section of the SF-OAK bridge to collapse. It fell into the lower deck, but did not cause the lower deck to give way. This seems to indicate they had better tolerances (higher safery factor). But that may be a very naive take.
The article mentions this. Common engineering practice today is to avoid any single points of failure, but back when this was built, the profession was high on precision engineering based off modern finite element models and other ways to more exactly determine the capacity of a bridge.
It was deliberately built without redundancy, because they thought they could achieve perfection. In fact the models they used were correct -- it was the underlying assumptions about the long-term behaviour of the materials used that were wrong.
This isn't the first such collapse, and it likely won't be the last, but it's safe to say that engineers have learned from their failures. Modern standards generally maximize redundancy. Precision is used to reliably achieve a high margin of error, rather than to get away with the minimum possible.
> But engineers gradually recognized that the structure had so few crucial supports that if even one of them failed, an entire section could collapse.
> “There is no robustness, or the possibility of redistribution of the forces,” said Massimo Majowiecki, an architect and engineer in Bologna, northern Italy.
> That lack of redundancy, as it is now often called, “is not necessarily inconsistent with how bridges were designed in the 1960s,” said Donald Dusenberry, a structural engineer with Simpson Gumpertz & Heger in Boston.
The design was such that as long as all of the parts worked, it remained standing. But it was also such that a very small number of failures would push the remaining supports beyond their capacity to withstand the loads, leading to collapse.
The SF-OAK bridge likely had a much higher level of what this article calls "redundancy" or more generally of simply "over design" (design for loads some multiple of normal loading) such that collapse of the top deck did not push the lower deck beyond its load holding capacity. I'm surprised that "bridge design in the '60s" (as stated in the article) did not take these details into account.
Given that the collapse happened during a thunder storm, and given that there are reports of a lightning strike prior to the collapse [1]: how likely is it that water accumulated inside the prestressed concrete hull was suddenly evaporated by a lightning strike, effectively blowing the cable stay up? I remember reading about this theory in some interview, but never heard anything about it since.
This would have been perfect situation for some destructive testing.
During night time block all traffic. Then drive radio controlled, overloaded trucks over the bridge every six months.
If the bridge fails, you just saved human lives. If it doesn't, the cost of that project is relatively small compared to pre-emptive repairs. The likelihood of regular load destroying the bridge in the meantime could be managed to be negligible.
It's already used with pressure vessels, because hydraulic testing of them is very safe. Now you would no longer need suicidal truck drivers to do it on bridges.
The EU is clearly valuable to many of its partners as a domestic scapegoat. The problems come when people actually believe them and try to 'solve' the problems 'caused' by them and find a stack of disasters that makes being the prime minister a position competed /against/ becoming instead of /for/.
In the last drone video at the end of the article, the sun is quite low in the sky, making the shadows of people and tractors stretch out and play against the shapes. A horrible scene, but the scale and depth and shadows are visually stunning!
Are there any experts here who can elaborate on whether Professor Gentile's acoustic testing of the bridge's cable stays may have had any negative effect on its stability?
Be super careful with that line of thought: it is precisely what they will use to deflect blame from the construction, engineering, and maintenance issues. "The bridge wouldn't have failed if it weren't for that pesky diagnostic procedure that also happened to raise all sorts of problems about corrosion and structural integrity"
edit: also - not an expert but interested and somewhat informed - this is a very common structural engineering technique and should under no circumstances, ever, lead to this kind of outcome on a sound structure.
You may want to get in touch with [Professor Raimondo Betti][1], who [I spoke][2] with at Columbia University prior to a talk he gave about his research on [a bridge cable corrosion monitoring system][3].
He was optimistic about the ability of his (from my understanding, passive) sensor system in helping prevent these tragedies, but pessimistic about the political will to apply it to bridges.
Reading that paper, it seems it solely comprises attaching sensors (I'd imagine piezo transducers bolted firmly onto measurement points, most likely) and listening - so it's hard to see how it could have had any effect, unless they attached the sensors with a method that would damage the bridge, which seems unlikely.
What I find unusual is - according to the infographic - both southern cables broke in the initial stage. And then that was followed by the northern cables breaking in response to the load shifting.
I presume the two southern cables are independent components and support independent platforms. Why would they both break at the same time, if not for some exogenous event?
It’s amazing to me in this day in age that there are no actual videos of the collapse. Not even from a car camera. I’ve searched everywhere and it would really be a very useful piece of information to have in order to diagnose what really happened.
Per the article, the collapse was recorded by a security camera and the footage is being analyzed by the investigators, but it has not been made public yet.
It cost ~4-5x times more than regular (today, not sure decades ago) but total cost of bridge build for it's majority was probably (overpriced) labor anyways.
In machinery stainless steels have universally poorer mechanical properties vs non-stainless alloys - a reduced corrosion rate is about the only benefit, and even so, it's still just "stain-less" — not "stain-free" — over the timescales of civil infrastructure, it would likely suffer damaging corrosion at some point.
The price ratio is roughly 6 historically, it has lowered to as low as 4 only recently, and stainless steel has been largely used, since the '80's, instead of conventional rebar steel.
But there is no stainless steel capable of having the same resistance/elasticity of cable steel.
To give you some comparative data in EU the normal rebar since more than 40 years is usually grade 44 or 45 that means that it starts elongating (and eventually fail) around 4300-4500 Kg/cm2 and breaks over 5400 Kg/cm2 (still as a reference normally the calculation uses a max of 2600 Kg/cm2).
Cable steel (again since more than 40 years), typically in 7 wire strands, is almost 4 times stronger, the same values are 16700 kg/cm2 and 18600 kg/cm2.
Typically it is pre-stressed to 12500-13600 kg/cm2.
Stainless steel cable is used in the fixed rigging (mast stays) of yachts precisely because of it's anti-rusting properties. Unfortunately the stainless still has to be completely replaced every 5-10 years because it weakens to the point you can't insure the yacht anymore.
Stainless has a very different failure mode to normal steel where a tiny nick in the surface of the stainless under tension forms a crack and corrosion occurs in the very bottom of the crack making it propagate deeper into the stainless until it fails while still looking shiny on the outside.
[+] [-] acomjean|7 years ago|reply
One of my first tasks as an intern at the Army Corp Of Engineers was to create 6 inspection packets (copies of every part) of the cape cod canal bridge, which was being inspected.
I know the tappan-zee bridge was replaced because the old one was just too old (designed to last 50 years, it was replaced at over 60 years).
https://en.wikipedia.org/wiki/Tappan_Zee_Bridge_(1955–2017)#...
One of the reason I left the engineering profession is no one wants to pay for it so it gets "deferred". The US's bridges get a c+ according to the American Society Of Civil Engineers.
https://www.infrastructurereportcard.org/cat-item/bridges/
I'm also a little curious why the cables were wrapped in concrete. Steel cables are common on bridges. stability side to side? Concrete is not great in tension (steel is very good in tension). As the article indicates, it was potentially hiding some of the cable corrosion, making the situation worse.
[+] [-] GuB-42|7 years ago|reply
It is pre-stressed concrete, it is working in compression against the cable tension. The idea is that as the load increases, instead of pulling directly on the cables, it just decompresses the concrete.
You can think of the cable as a spring, with the bridge suspended it. As you walk on the bridge, it bounces. To prevent the bouncing, you can put the spring under high tension into a rigid pipe, with the ends of the spring attached to the ends of the pipe. This way, as you walk on the bridge, the spring tension will stay constant, only the compression on the pipe will vary.
[+] [-] sharkmerry|7 years ago|reply
the concrete was meant to be a protective sheath to stop cable corrosion. poor materials engineering at the time sounds like the issue
>> He believed using the system would reduce the sway of the bridge. Structural engineers seemed to agree.
But Mr. Morandi also believed that the concrete coating would protect the steel cables inside from the wear and tear of the elements.
“Concrete structures seemed to be eternal,” Mr. Majowiecki said. “This was the mentality.”
In that hope, he added, Mr. Morandi was greatly mistaken.
The concrete of the day turned out to be highly vulnerable to degradation, worsened perhaps by salty air from the Mediterranean Sea and the harsh fumes from nearby factories.
Cracks in the concrete shell let water in, and the steel began corroding almost as soon as the bridge was opened for traffic in 1967. But unlike bare cables, any corrosion was hidden deep inside, making it hard to detect."
[+] [-] microcolonel|7 years ago|reply
[deleted]
[+] [-] matant|7 years ago|reply
[+] [-] jaclaz|7 years ago|reply
https://www.ingenio-web.it/20966-il-crollo-del-ponte-morandi...
https://www.ingenio-web.it/20925-il-viadotto-sul-polcevera-e...
https://www.ingenio-web.it/20939-ing-camomilla-come-e-perche...
[+] [-] lozzo|7 years ago|reply
[deleted]
[+] [-] walterstucco|7 years ago|reply
The best piece I've read about the disaster
[+] [-] dmurray|7 years ago|reply
It would be very interesting to know what he had to say about the other 299 bridges. After all, you can find someone who will tell you you have a structural problem with the safest bridge. It's hard to tell if they are a crank, someone with a vested interest, someone seeking publicity for their new diagnostic method, or genuinely an expert who is giving you good advice. But if Professor Gentile mostly says the bridges are fine, but singled out this one as a danger - then it's really worth listening to his other recommendations.
[+] [-] shkkmo|7 years ago|reply
[+] [-] SamuelAdams|7 years ago|reply
[+] [-] DonHopkins|7 years ago|reply
https://www.nytimes.com/interactive/2018/01/27/technology/so...
[+] [-] baxtr|7 years ago|reply
EDIT: the effect is really quite cool and actually useful unlike other animations!
[+] [-] gmiller123456|7 years ago|reply
[+] [-] ProAm|7 years ago|reply
[+] [-] dv_dt|7 years ago|reply
"Autostrade, which handles media queries on behalf of the subcontractor, Spea Engineering, declined to comment."
https://www.cbsnews.com/news/italy-bridge-collapse-genoa-atl...
https://en.wikipedia.org/wiki/Atlantia_(company)
The technical specifics of the bridge collapse are interesting, but the privatization of multiple road systems should have in theory let the company be cognizant of the systemic issues of the design practices of various eras, but how was this missed? The company was managing the bridge since 1999, almost twenty years now. This is as much or more of an organizational question as well as a private vs public ownership question as it is a technical one.
[+] [-] aboodman|7 years ago|reply
> He warned the company that manages the bridge, Autostrade per l’Italia, or Highways for Italy, but he said that it never followed up on his recommendation to perform a fuller computer study and to outfit the bridge with permanent sensors.
> For reasons it has not fully explained, Autostrade, which took over management of the bridge in 1999, did not carry out the same operation on the supports of the other two towers — including the tower that collapsed.
> Autostrade won the concession to run nearly half of Italy’s highways from a cash-strapped Italian government, starting in 1999. After that, there were no major renovations of the Morandi bridge.
... etc ...
[+] [-] Aloha|7 years ago|reply
"Autostrade won the concession to run nearly half of Italy’s highways from a cash-strapped Italian government, starting in 1999. After that, there were no major renovations of the Morandi bridge."
[+] [-] lbeltrame|7 years ago|reply
That's not correct. They're not privately owned: they're a sort of lease (I can't quite translate "concessione") because the government is still technically the one who onws it.
And for those other HN readers, there's also a public-owned company that handles roads, Anas, which is not doing well with regards to maintenance (this just to put into perspective that's not just a public vs private thing).
[+] [-] walterstucco|7 years ago|reply
[deleted]
[+] [-] UAREWRONG|7 years ago|reply
[deleted]
[+] [-] dmix|7 years ago|reply
Whenever I read about these incidents, with only one camera angle, I almost want to buy a camera and point it outwards from my apartment just in case I catch something like this happening in my city.
[+] [-] tlb|7 years ago|reply
[+] [-] mc32|7 years ago|reply
[+] [-] Filligree|7 years ago|reply
It was deliberately built without redundancy, because they thought they could achieve perfection. In fact the models they used were correct -- it was the underlying assumptions about the long-term behaviour of the materials used that were wrong.
This isn't the first such collapse, and it likely won't be the last, but it's safe to say that engineers have learned from their failures. Modern standards generally maximize redundancy. Precision is used to reliably achieve a high margin of error, rather than to get away with the minimum possible.
[+] [-] pwg|7 years ago|reply
> But engineers gradually recognized that the structure had so few crucial supports that if even one of them failed, an entire section could collapse.
> “There is no robustness, or the possibility of redistribution of the forces,” said Massimo Majowiecki, an architect and engineer in Bologna, northern Italy.
> That lack of redundancy, as it is now often called, “is not necessarily inconsistent with how bridges were designed in the 1960s,” said Donald Dusenberry, a structural engineer with Simpson Gumpertz & Heger in Boston.
The design was such that as long as all of the parts worked, it remained standing. But it was also such that a very small number of failures would push the remaining supports beyond their capacity to withstand the loads, leading to collapse.
The SF-OAK bridge likely had a much higher level of what this article calls "redundancy" or more generally of simply "over design" (design for loads some multiple of normal loading) such that collapse of the top deck did not push the lower deck beyond its load holding capacity. I'm surprised that "bridge design in the '60s" (as stated in the article) did not take these details into account.
[+] [-] jakelarkin|7 years ago|reply
[+] [-] lqet|7 years ago|reply
[1] https://www.dw.com/en/speculation-mounts-over-genoa-bridge-c...
[+] [-] jaclaz|7 years ago|reply
[+] [-] unknown|7 years ago|reply
[deleted]
[+] [-] vlehto|7 years ago|reply
During night time block all traffic. Then drive radio controlled, overloaded trucks over the bridge every six months.
If the bridge fails, you just saved human lives. If it doesn't, the cost of that project is relatively small compared to pre-emptive repairs. The likelihood of regular load destroying the bridge in the meantime could be managed to be negligible.
It's already used with pressure vessels, because hydraulic testing of them is very safe. Now you would no longer need suicidal truck drivers to do it on bridges.
[+] [-] Ndymium|7 years ago|reply
[+] [-] PunchTornado|7 years ago|reply
When the EU encourages investments in infrastructure.
Go figure.
[+] [-] Nasrudith|7 years ago|reply
[+] [-] DonHopkins|7 years ago|reply
[+] [-] stcredzero|7 years ago|reply
[+] [-] lqet|7 years ago|reply
I found this paper on the method: https://www.ndt.net/article/jae/papers/20-083.pdf
E: as mentioned below, the method is completely passive.
[+] [-] throwaway5752|7 years ago|reply
edit: also - not an expert but interested and somewhat informed - this is a very common structural engineering technique and should under no circumstances, ever, lead to this kind of outcome on a sound structure.
[+] [-] hypertexthero|7 years ago|reply
He was optimistic about the ability of his (from my understanding, passive) sensor system in helping prevent these tragedies, but pessimistic about the political will to apply it to bridges.
[1]: http://civil.columbia.edu/raimondo-betti
[2]: https://www.simongriffee.com/notebook/GRS-20151015-100821/
[3]: https://www.youtube.com/watch?v=cP1CfGVVXO4
[+] [-] madaxe_again|7 years ago|reply
[+] [-] stillsut|7 years ago|reply
I presume the two southern cables are independent components and support independent platforms. Why would they both break at the same time, if not for some exogenous event?
[+] [-] sonar_un|7 years ago|reply
[+] [-] jpatokal|7 years ago|reply
[+] [-] gesman|7 years ago|reply
It cost ~4-5x times more than regular (today, not sure decades ago) but total cost of bridge build for it's majority was probably (overpriced) labor anyways.
[+] [-] AceyMan|7 years ago|reply
[+] [-] jaclaz|7 years ago|reply
But there is no stainless steel capable of having the same resistance/elasticity of cable steel.
To give you some comparative data in EU the normal rebar since more than 40 years is usually grade 44 or 45 that means that it starts elongating (and eventually fail) around 4300-4500 Kg/cm2 and breaks over 5400 Kg/cm2 (still as a reference normally the calculation uses a max of 2600 Kg/cm2).
Cable steel (again since more than 40 years), typically in 7 wire strands, is almost 4 times stronger, the same values are 16700 kg/cm2 and 18600 kg/cm2.
Typically it is pre-stressed to 12500-13600 kg/cm2.
[+] [-] ralphhughes|7 years ago|reply
Stainless has a very different failure mode to normal steel where a tiny nick in the surface of the stainless under tension forms a crack and corrosion occurs in the very bottom of the crack making it propagate deeper into the stainless until it fails while still looking shiny on the outside.
[+] [-] unknown|7 years ago|reply
[deleted]