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Genoa Bridge Collapse: The Road to Tragedy

238 points by conroy 8y ago

stcredzero 8y ago
For the prudent, form follows function. Doing things because you can, because it's "neat" is courting folly. There is an analogy here for coding.
SamuelAdams 8y ago
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.
- baxtr 8y ago
  Thanks, now I have to click the link ;-) EDIT: the effect is really quite cool and actually useful unlike other animations!
- DonHopkins 8y ago
  NYT is famous for their beautiful yet informative scrolling infographics: https://www.nytimes.com/interactive/2018/01/27/technology/social-media-bots.html https://www.nytimes.com/interactive/2018/01/27/technology/so...
- ProAm 8y ago
  I found the opposite, that article is really irritating to read, I gave up a few pages down.
- gmiller123456 8y ago
  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.
lqet 8y ago
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? I found this paper on the method: https://www.ndt.net/article/jae/papers/20-083.pdf https://www.ndt.net/article/jae/papers/20-083.pdf E: as mentioned below, the method is completely passive.
- hypertexthero 8y ago
  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. [1]: http://civil.columbia.edu/raimondo-betti http://civil.columbia.edu/raimondo-betti [2]: https://www.simongriffee.com/notebook/GRS-20151015-100821/ https://www.simongriffee.com/notebook/GRS-20151015-100821/ [3]: https://www.youtube.com/watch?v=cP1CfGVVXO4 https://www.youtube.com/watch?v=cP1CfGVVXO4
  - lqet 8y ago
    Many thanks! Just out of curiosity: why was he pessimistic about the political will to apply this method? Because politicians fear the results?
    - hypertexthero 8y ago
      I am not sure, but that sounds right. This was a few years ago and my memory may be faulty, but I remember him saying that it would probably take the collapse of a large bridge like the Brooklyn or George Washington bridges in NYC before the authorities in the city would consider using the system.
    - jandrese 8y ago
      From a political standpoint you are spending money that might tell you that you need to blow your budget on rebuilding some infrastructure right now. Bridge collapses are so rare that nobody thinks it will happen to them. Just ask the people of Minneapolis.
mc32 8y ago
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.
- Filligree 8y ago
  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.
  - mc32 8y ago
    So in some respect older bridges were overengineered to compensate for the lack of good modeling. Then good modelling came along and gave engineers overconfidence, now this is being corrected with better understading of materials science? And thanks for pointing out that reliance on precision engineering might have led to safety factor reduction due perhaps to overconfidence...
    - garmaine 8y ago
      Better understanding of materials, and better recognition that “once in a century” events do happen.
      - 8y ago
matant 8y ago
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!
- jaclaz 8y ago
  JFYI (Italian) among many others, these are the more technical ones: https://www.ingenio-web.it/20966-il-crollo-del-ponte-morandi-a-genova https://www.ingenio-web.it/20966-il-crollo-del-ponte-morandi... https://www.ingenio-web.it/20925-il-viadotto-sul-polcevera-ecco-larticolo-di-riccardo-morandi-del-1967-con-tutti-i-dettagli-progettuali https://www.ingenio-web.it/20925-il-viadotto-sul-polcevera-e... https://www.ingenio-web.it/20939-ing-camomilla-come-e-perche-intervenimmo-sugli-stralli-della-pila-11-del-ponte-morandi-nel-1992 https://www.ingenio-web.it/20939-ing-camomilla-come-e-perche...
  - pb060 8y ago
    True, but those are technical ones. I couldn't find any article explaining what a "strallo" is, in fact "cos'è uno strallo" (what is a straw) seems to be a common search based on Google's autocomplete.
    - jaclaz 8y ago
      >True, but those are technical ones. I couldn't find any article explaining what a "strallo" is, in fact "cos'è uno strallo" (what is a straw) seems to be a common search based on Google's autocomplete. It's not a "straw", it is a "stay" in English. Strallo is a term mutuated from boats, a sail boat has a mast (albero) that is kept vertical and strong by one or more sets of "stays" (stralli): https://en.wikipedia.org/wiki/Stays_(nautical) https://en.wikipedia.org/wiki/Stays_(nautical) https://it.wikipedia.org/wiki/Strallo_(vela) https://it.wikipedia.org/wiki/Strallo_(vela) On the sail boat the function of the stay is "opposite" to that of a bridge stay, it is used to keep the mast pressed to the base and more rigid, on a bridge they are simply "suspension supports" allowing to carry the weight of the viaduct deck and transferring the vertical load to the tower or pylon (torre o antenna). https://en.wikipedia.org/wiki/Cable-stayed_bridge https://en.wikipedia.org/wiki/Cable-stayed_bridge https://it.wikipedia.org/wiki/Strallo_(ingegneria) https://it.wikipedia.org/wiki/Strallo_(ingegneria)
dmix 8y ago
> 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.
- tlb 8y ago
  An artist in New York took a picture out his window almost every day for 11 years with a large-format film camera. He indeed caught something notable. https://www.amazon.com/Window-Septembers-1995-2005-Reiner-Leist/dp/3791336797 https://www.amazon.com/Window-Septembers-1995-2005-Reiner-Le...
  - dmix 8y ago
    What a perfect example... I need to do this one day! Thanks for the link
  - benchtobedside 8y ago
    For anyone wondering what he caught: "The resulting bulk of around 2,200 photographs documents both the every-day life and change of Manhattan, including the historic event of the destruction of the World Trade Center on September 11, 2001" -- https://en.wikipedia.org/wiki/Reiner_Leist https://en.wikipedia.org/wiki/Reiner_Leist
lqet 8y ago
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. [1] https://www.dw.com/en/speculation-mounts-over-genoa-bridge-collapse/a-45084494 https://www.dw.com/en/speculation-mounts-over-genoa-bridge-c...
- jaclaz 8y ago
  IMHO not more or less unlikely, simply impossible.
  - lqet 8y ago
    I am no expert in this field, so: why are you so sure this is impossible? If I understand it correctly, a lightning strike to the (already slightly damaged) cable stays will seek its way through the steel cables, heating them up. If there is water between the cables and the concrete, a small steam explosion will occur. If the cables are already corroded (which they were, according to the article) and thus brittle, this may cause heavy damage to them. As the mentioned corrosion is indicative of water present, and since the cable stays are a single point of failure (also explained in the article), I personally find this a quite likely chain of events.
    - megous 8y ago
      Presumably the bridge had a lightning protection system installed.
    - jaclaz 8y ago
      Check a representation of one of the stays, here: https://static01.nyt.com/newsgraphics/2018/08/27/italy-bridge/0b40f75c7cf935f2ee7d76ff188d2d3a92f8c15f/cutaway-diagram-600.jpg https://static01.nyt.com/newsgraphics/2018/08/27/italy-bridg... Basically the concrete around the steel cables is nothing but a "protection box". From the little I know about explosions, the idea is that there is a sudden expansion from the inside to the outside. For having any damage to parts near the "core" there must be sufficient "containment", that the concrete simply cannot represent IMHO. The actual steel used for cables is high tensile and - believe me - extremely resistant besides rather hard while concrete (particularly concrete so ammalorated to let the water creep in) has very little tensile strength. So, IF actually there was a steam explosion, the result/effect would have been much more likely (besides "nothing") unscathed cables and ruined concrete around them (with no structural failure of the bridge) As an alternative to explosives it is common to use expanding cement grout in actual concrete demolition, which essentially is explosive on slow motion. When dealing with reinforced concrete you normally need to cut the rebars with a torch (or other means) after the concrete has cracked. Check (just an example this kind of cement originated in Japan in the '70's and now there are more similar products than stars in the sky): https://www.youtube.com/watch?v=7cvcnkzK8Jk https://www.youtube.com/watch?v=7cvcnkzK8Jk
PunchTornado 8y ago
And the Interior Minister says that the EU is to blame because it doesn't allow them to invest in infrastructure. When the EU encourages investments in infrastructure. Go figure.
- Nasrudith 8y ago
  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/.
DonHopkins 8y ago
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!
dv_dt 8y ago
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." https://www.cbsnews.com/news/italy-bridge-collapse-genoa-atlantia-autostrade-concession-with-causes-unclear/ https://www.cbsnews.com/news/italy-bridge-collapse-genoa-atl... https://en.wikipedia.org/wiki/Atlantia_(company) 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.
- UAREWRONG 8y ago
  bro you are dead wrong. dead wrong. LITERALLY FROM THE ARTICLE "There is now fierce debate in Italy over whether the company did in fact do enough — along with calls to roll back the privatization of much of Italy’s roadways. 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. In late 2017 or early 2018, tests indicated that the bridge had weakened by an “average” of 10 to 20 percent, Roberto Ferrazza, superintendent at the local ministry of infrastructure and transportation, told The Times in an interview. Experts in bridge construction say it is notoriously difficult to measure the exact amount of degradation of steel elements buried in concrete, in the way that they are on the Morandi bridge. “There’s nothing more imprecise than trying to evaluate the condition of internal cables,” said Gary J. Klein, a member of the National Academy of Engineering in the United States who studies structural failures and is executive vice president at Wiss, Janney, Elstner, an engineering and architecture firm in Northbrook, Ill. “It’s a very imperfect science.” Because the weakest point could be anywhere on the structure, Mr. Klein added, “you have to be in the right place at the right time, and so I’m very skeptical of the accuracy of any such estimate.” A decision was made, by Autostrade in accordance with the Ministry of Infrastructure, to refurbish and repair the stays on two towers, including the one that would collapse. But the work was not yet scheduled."
gesman 8y ago
Use stainless steel cable instead? 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 8y ago
  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.
- jaclaz 8y ago
  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.
- ralphhughes 8y ago
  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 8y ago
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). https://en.wikipedia.org/wiki/Tappan_Zee_Bridge_(1955–2017)#Replacement_bridge 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/ 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.
- sharkmerry 8y ago
  >> 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."
  - acomjean 8y ago
deleted 8y ago
[deleted]
dmurray 8y ago
> 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.
- shkkmo 8y ago
  Since he was contracted to do the inspection, I presume they found his diagnostic method credible.
sonar_un 8y ago
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.
- jpatokal 8y ago
  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.
vlehto 8y ago
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.
- Ndymium 8y ago
  You forget that there are houses below the bridge, that could have been crushed. Not exactly a place for destructive testing.
  - vlehto 8y ago
    If the bridge is fine, there is no problem. If the bridge is rotten, you have lot fewer victims. You want to do pre-emptive repairs? OK, the bridge ought to be fine. We can then proceed with the destructive testing. You could do the testing with something like 110% of the typical max traffic load. A rotten bridge would then collapse within 6 months of it's "natural collapse". Only things you do is to make the collapse more predictable and you save lives.
    - Ndymium 8y ago
      I don't think a testing method where there is a risk of a lot of innocent people dying is going to be accepted anywhere. I guess that is the dilemma with these situations.
      - vlehto 8y ago
        Would not be the first time saving lives ends up being less important than avoiding responsibility. So I agree on your prediction.
  - 8y ago
stillsut 8y ago
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?

238 points by conroy 8y ago

For the prudent, form follows function. Doing things because you can, because it's "neat" is courting folly. There is an analogy here for coding.

SamuelAdams 8y ago

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.

baxtr 8y ago
Thanks, now I have to click the link ;-) EDIT: the effect is really quite cool and actually useful unlike other animations!
DonHopkins 8y ago
NYT is famous for their beautiful yet informative scrolling infographics: https://www.nytimes.com/interactive/2018/01/27/technology/social-media-bots.html https://www.nytimes.com/interactive/2018/01/27/technology/so...
ProAm 8y ago
I found the opposite, that article is really irritating to read, I gave up a few pages down.
gmiller123456 8y ago
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.

lqet 8y ago

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? I found this paper on the method: https://www.ndt.net/article/jae/papers/20-083.pdf https://www.ndt.net/article/jae/papers/20-083.pdf E: as mentioned below, the method is completely passive.

hypertexthero 8y ago
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. [1]: http://civil.columbia.edu/raimondo-betti http://civil.columbia.edu/raimondo-betti [2]: https://www.simongriffee.com/notebook/GRS-20151015-100821/ https://www.simongriffee.com/notebook/GRS-20151015-100821/ [3]: https://www.youtube.com/watch?v=cP1CfGVVXO4 https://www.youtube.com/watch?v=cP1CfGVVXO4
- lqet 8y ago
  Many thanks! Just out of curiosity: why was he pessimistic about the political will to apply this method? Because politicians fear the results?
  - hypertexthero 8y ago
    I am not sure, but that sounds right. This was a few years ago and my memory may be faulty, but I remember him saying that it would probably take the collapse of a large bridge like the Brooklyn or George Washington bridges in NYC before the authorities in the city would consider using the system.
  - jandrese 8y ago
    From a political standpoint you are spending money that might tell you that you need to blow your budget on rebuilding some infrastructure right now. Bridge collapses are so rare that nobody thinks it will happen to them. Just ask the people of Minneapolis.

mc32 8y ago

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.

Filligree 8y ago
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.
- mc32 8y ago
  So in some respect older bridges were overengineered to compensate for the lack of good modeling. Then good modelling came along and gave engineers overconfidence, now this is being corrected with better understading of materials science? And thanks for pointing out that reliance on precision engineering might have led to safety factor reduction due perhaps to overconfidence...
  - garmaine 8y ago
    Better understanding of materials, and better recognition that “once in a century” events do happen.
    - 8y ago

matant 8y ago

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!

jaclaz 8y ago
JFYI (Italian) among many others, these are the more technical ones: https://www.ingenio-web.it/20966-il-crollo-del-ponte-morandi-a-genova https://www.ingenio-web.it/20966-il-crollo-del-ponte-morandi... https://www.ingenio-web.it/20925-il-viadotto-sul-polcevera-ecco-larticolo-di-riccardo-morandi-del-1967-con-tutti-i-dettagli-progettuali https://www.ingenio-web.it/20925-il-viadotto-sul-polcevera-e... https://www.ingenio-web.it/20939-ing-camomilla-come-e-perche-intervenimmo-sugli-stralli-della-pila-11-del-ponte-morandi-nel-1992 https://www.ingenio-web.it/20939-ing-camomilla-come-e-perche...
- pb060 8y ago
  True, but those are technical ones. I couldn't find any article explaining what a "strallo" is, in fact "cos'è uno strallo" (what is a straw) seems to be a common search based on Google's autocomplete.
  - jaclaz 8y ago
    >True, but those are technical ones. I couldn't find any article explaining what a "strallo" is, in fact "cos'è uno strallo" (what is a straw) seems to be a common search based on Google's autocomplete. It's not a "straw", it is a "stay" in English. Strallo is a term mutuated from boats, a sail boat has a mast (albero) that is kept vertical and strong by one or more sets of "stays" (stralli): https://en.wikipedia.org/wiki/Stays_(nautical) https://en.wikipedia.org/wiki/Stays_(nautical) https://it.wikipedia.org/wiki/Strallo_(vela) https://it.wikipedia.org/wiki/Strallo_(vela) On the sail boat the function of the stay is "opposite" to that of a bridge stay, it is used to keep the mast pressed to the base and more rigid, on a bridge they are simply "suspension supports" allowing to carry the weight of the viaduct deck and transferring the vertical load to the tower or pylon (torre o antenna). https://en.wikipedia.org/wiki/Cable-stayed_bridge https://en.wikipedia.org/wiki/Cable-stayed_bridge https://it.wikipedia.org/wiki/Strallo_(ingegneria) https://it.wikipedia.org/wiki/Strallo_(ingegneria)

dmix 8y ago

> 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.

tlb 8y ago
An artist in New York took a picture out his window almost every day for 11 years with a large-format film camera. He indeed caught something notable. https://www.amazon.com/Window-Septembers-1995-2005-Reiner-Leist/dp/3791336797 https://www.amazon.com/Window-Septembers-1995-2005-Reiner-Le...
- dmix 8y ago
  What a perfect example... I need to do this one day! Thanks for the link
- benchtobedside 8y ago
  For anyone wondering what he caught: "The resulting bulk of around 2,200 photographs documents both the every-day life and change of Manhattan, including the historic event of the destruction of the World Trade Center on September 11, 2001" -- https://en.wikipedia.org/wiki/Reiner_Leist https://en.wikipedia.org/wiki/Reiner_Leist

lqet 8y ago

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. [1] https://www.dw.com/en/speculation-mounts-over-genoa-bridge-collapse/a-45084494 https://www.dw.com/en/speculation-mounts-over-genoa-bridge-c...

jaclaz 8y ago
IMHO not more or less unlikely, simply impossible.
- lqet 8y ago
  I am no expert in this field, so: why are you so sure this is impossible? If I understand it correctly, a lightning strike to the (already slightly damaged) cable stays will seek its way through the steel cables, heating them up. If there is water between the cables and the concrete, a small steam explosion will occur. If the cables are already corroded (which they were, according to the article) and thus brittle, this may cause heavy damage to them. As the mentioned corrosion is indicative of water present, and since the cable stays are a single point of failure (also explained in the article), I personally find this a quite likely chain of events.
  - megous 8y ago
    Presumably the bridge had a lightning protection system installed.
  - jaclaz 8y ago
    Check a representation of one of the stays, here: https://static01.nyt.com/newsgraphics/2018/08/27/italy-bridge/0b40f75c7cf935f2ee7d76ff188d2d3a92f8c15f/cutaway-diagram-600.jpg https://static01.nyt.com/newsgraphics/2018/08/27/italy-bridg... Basically the concrete around the steel cables is nothing but a "protection box". From the little I know about explosions, the idea is that there is a sudden expansion from the inside to the outside. For having any damage to parts near the "core" there must be sufficient "containment", that the concrete simply cannot represent IMHO. The actual steel used for cables is high tensile and - believe me - extremely resistant besides rather hard while concrete (particularly concrete so ammalorated to let the water creep in) has very little tensile strength. So, IF actually there was a steam explosion, the result/effect would have been much more likely (besides "nothing") unscathed cables and ruined concrete around them (with no structural failure of the bridge) As an alternative to explosives it is common to use expanding cement grout in actual concrete demolition, which essentially is explosive on slow motion. When dealing with reinforced concrete you normally need to cut the rebars with a torch (or other means) after the concrete has cracked. Check (just an example this kind of cement originated in Japan in the '70's and now there are more similar products than stars in the sky): https://www.youtube.com/watch?v=7cvcnkzK8Jk https://www.youtube.com/watch?v=7cvcnkzK8Jk

PunchTornado 8y ago

And the Interior Minister says that the EU is to blame because it doesn't allow them to invest in infrastructure. When the EU encourages investments in infrastructure. Go figure.

Nasrudith 8y ago
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/.

DonHopkins 8y ago

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!

dv_dt 8y ago

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." https://www.cbsnews.com/news/italy-bridge-collapse-genoa-atlantia-autostrade-concession-with-causes-unclear/ https://www.cbsnews.com/news/italy-bridge-collapse-genoa-atl... https://en.wikipedia.org/wiki/Atlantia_(company) 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.

UAREWRONG 8y ago
bro you are dead wrong. dead wrong. LITERALLY FROM THE ARTICLE "There is now fierce debate in Italy over whether the company did in fact do enough — along with calls to roll back the privatization of much of Italy’s roadways. 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. In late 2017 or early 2018, tests indicated that the bridge had weakened by an “average” of 10 to 20 percent, Roberto Ferrazza, superintendent at the local ministry of infrastructure and transportation, told The Times in an interview. Experts in bridge construction say it is notoriously difficult to measure the exact amount of degradation of steel elements buried in concrete, in the way that they are on the Morandi bridge. “There’s nothing more imprecise than trying to evaluate the condition of internal cables,” said Gary J. Klein, a member of the National Academy of Engineering in the United States who studies structural failures and is executive vice president at Wiss, Janney, Elstner, an engineering and architecture firm in Northbrook, Ill. “It’s a very imperfect science.” Because the weakest point could be anywhere on the structure, Mr. Klein added, “you have to be in the right place at the right time, and so I’m very skeptical of the accuracy of any such estimate.” A decision was made, by Autostrade in accordance with the Ministry of Infrastructure, to refurbish and repair the stays on two towers, including the one that would collapse. But the work was not yet scheduled."

gesman 8y ago

Use stainless steel cable instead? 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 8y ago
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.
jaclaz 8y ago
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.
ralphhughes 8y ago
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 8y ago

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). https://en.wikipedia.org/wiki/Tappan_Zee_Bridge_(1955–2017)#Replacement_bridge 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/ 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.

sharkmerry 8y ago
>> 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."
- acomjean 8y ago

deleted 8y ago

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dmurray 8y ago

> 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.

shkkmo 8y ago
Since he was contracted to do the inspection, I presume they found his diagnostic method credible.

sonar_un 8y ago

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.

jpatokal 8y ago
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.

vlehto 8y ago

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.

Ndymium 8y ago
You forget that there are houses below the bridge, that could have been crushed. Not exactly a place for destructive testing.
- vlehto 8y ago
  If the bridge is fine, there is no problem. If the bridge is rotten, you have lot fewer victims. You want to do pre-emptive repairs? OK, the bridge ought to be fine. We can then proceed with the destructive testing. You could do the testing with something like 110% of the typical max traffic load. A rotten bridge would then collapse within 6 months of it's "natural collapse". Only things you do is to make the collapse more predictable and you save lives.
  - Ndymium 8y ago
    I don't think a testing method where there is a risk of a lot of innocent people dying is going to be accepted anywhere. I guess that is the dilemma with these situations.
    - vlehto 8y ago
      Would not be the first time saving lives ends up being less important than avoiding responsibility. So I agree on your prediction.
- 8y ago

stillsut 8y ago

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?