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Featured Bridge Collapse Genoa - Informed Engineering Perspectives

  1. Aug 15, 2018 #1

    epenguin

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    The dramatic collapse of a bridge in Italy with many fatalities has been the big item of news all over Europe.
    https://www.theguardian.com/world/2...-death-toll-italy-minister-calls-resignations and many other reports.

    I just wonder if the qualified people here can throw any light not on the specifics which would be hard for them to know, but in general.

    I mean bridges are supposed to stay up. Engineers are famous for knowing how to construct bridges. For doing calculations on bridges, that is something they are famous for. And they are pretty successful because bridges generally stay up.

    I realise they cannot be left to themselves to stay up, but require checking and maintenance from time to time. Worrying thing, that does not seem to me at all easy. The temples of antiquity, the Coliseum, I've been told, would still be standing intact if they had been maintained. That what throws them down is plant life, inserting itself between the stones etc (as well as the edifices being used as convenient quarries sometimes), but this can be seen superficially and could be prevented without any advanced technology. Whereas I think of the steel members that might be suffering, corroding or something, as buried deep inside concrete and quite invisible. Difficult.

    A distinguished engineer was asked for comments on BBC last evening, and was not particularly comforting. Said that bridge safety was 'a calculus of uncertainties'. Engineers would give an uncertain warning that it would be prudent to close a bridge for investigation, then it was up to someone else to assume the responsibility of the significant economic damage, a lot depends on them, of deciding whether or not to close them pending investigation.

    There are many of these often spectacular bridges in Italy, basically a mountainous country. There are a number, in my impressionistic memory a dozen or two in the autostrade into and out of Genoa and in the hundred or two kilometres of coastal autostrada South from there, (Where you are more at risk from the drivers than from bridge collapse, more there than anywhere else I know, but that's another matter). The link on the above article notes that there have been other collapses in Italy, put down to inadequate inspection and maintenance. One may suspect in construction too - cutting corners with the materials etc. relative to those specified. In other words corruption. Often enough in Italy buildings calculated to resist a given strength of earthquake have nevertheless collapsed for this reason. That explains why you see in the headline that immediately there is an assumption someone is to blame and a search for a culprit.

    It would be useful to hear from experts here what light they can shed on this, on the state of the art and how things are, can be, managed. The article also states "the bridge was a sort of jewel in Italian engineering, because at that time it was built with new engineering techniques."

    They can surely explain the striking way an entire section collapsed, One would expect it to break in one point, but then I suppose as it kind of pivoted, snaps in another?
     
    Last edited by a moderator: Aug 15, 2018
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  3. Aug 15, 2018 #2

    Astronuc

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    For some images - https://en.wikipedia.org/wiki/Ponte_Morandi
    and https://www.cbc.ca/news/world/bridge-collapse-genoa-italy-1.4784417

    Apparently, there has been some concern expressed regarding the age of the bridge and its design.

    Certainly, modern day methods of bridge design are more robust than they were 50 years ago.

    From several images, it seems the western tower (of three) collapsed. That's pretty significant. They'd want to determine the initial failure point, i.e., did the roadway span fail, one of the cables sets, or the tower itself (base or upper portion).

    Investigators will have to look at the design, construction and maintenance records, assuming that's possible. They'll look for signs of fatigue and corrosion (environmental degradation) of concrete, rebar and steel structures, as well as the design. With respect to design, they'd look for stress concentrations (both tensile and shear). They'll have to look at the quality of the concrete and steel used in the construction, and if possible, the construction methods.

    Static and dynamic loads are part of the design, so they'll want to understand if the design loads were adequate. Dynamic loads include vehicular traffic and weather, and seismic loads. They'll have to look to see if the failed tower had stable footing.
     
  4. Aug 15, 2018 #3

    tech99

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    The BBC reported that work was being carried out "to shore up the tower foundations". So that will be an area for investigation. They also show pictures of the cables, showing corrosion, and also some strengthening from a previous upgrade. Unusually the tension cables are in concrete, so corrosion and the impossibility of inspecting them must be an issue, especially in a marine area. BBC also report the number of cables is much less than present day practice, but I am uncertain what this means exactly.
    On the first suspension bridge across the River Severn in the UK, 1960s, I believe that microphones are installed which listen for wires breaking, and they are heard breaking all the time. Someone has to make a judgement, because such structures have a finite life.
     
  5. Aug 15, 2018 #4

    JBA

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    It will be interesting to see what they find/decide as the source of the failure.

    In the #4 post Wiki.... site "Construction" section there is a photo that if you click on it, the last picture selection to the right shows in red what section of the bridge collapsed; and, apart of short tie-in sections at each end, all of components in that section (bridge & tower components),other than the cables, are loaded in compression.
     
  6. Aug 15, 2018 #5

    anorlunda

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  7. Aug 15, 2018 #6

    JBA

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    Yes, in the section titled "Construction" there is a picture, if you click on that picture, it will open to larger view of that picture with an arrow on the left and right side, if you click on the arrow on the right side twice you will see the picture with the red area.
     
  8. Aug 15, 2018 #7
  9. Aug 15, 2018 #8
    I would submit that if wires are breaking, the design was faulty.
     
  10. Aug 15, 2018 #9

    JBA

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    In response to the above, it is also possible that the wires experienced environmental conditions and loadings that were not anticipated during the design some 50 years ago. Since the wires were breaking was a known problem, then the responsibility for the failure should not be assigned to the designers but to those responsible for seeing the bridge was adequately maintained.

    As someone that spent the last 20 years doing new product development of industrial pressure relief valves used extreme services, I can state that, unfortunately, no matter how diligently you design and select materials and how much pre-release testing you perform, the customer is going to be the ultimate test of any new product as to how it will perform and survive under his particular service conditions. That is the reason that we refused to specify any specific maintenance schedule for our valves; as an example, the maintenance schedule for a valve in a corrosive fluid or vapor service or a corrosive environment is drastically different from one in cryogenic service or in an enclosed plant environment etc.
     
  11. Aug 16, 2018 #10

    CWatters

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  12. Aug 16, 2018 #11

    nsaspook

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    That's interesting as a possible trigger in a weakened structure. The bolt current in the re-bar grid from a strike could have flash vaporized the water that had been absorbed by the concrete and caused it to expand so fast that it pulverized the areas immediately surrounding the re-bar in a shock wave of expanding gas. Similar to the effect when lightning strikes a live tree.

    https://www.concreteconstruction.net/how-to/lightning-damage-to-concrete_o
    https://www.facebook.com/ScottEvansTV/photos/pcb.1671244362891545/1671243309558317/?type=3&theater
    http://www.kwch.com/content/news/Lightning-strike-in-Wichita-creates-hole-in-concrete-417679823.html
     
    Last edited: Aug 16, 2018
  13. Aug 16, 2018 #12

    256bits

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    maybe I wasn't logged earlier and tried to post, and it's lost, but.....
    Cracking of concrete would accompanied with an electromagnetic field, oscillating, in the vicinity of the crack, as the stress suddenly is reduced along the crack length. Whether the field is strong enough to initiate an atmospheric lightning strike as a precursor to complete failure is something to look at. The lightning strike may not be the originator of the failure, but an indicator that complete failure is imminent.
    http://framcos.org/FraMCoS-7/01-12.pdf
     
  14. Aug 17, 2018 #13
    It was reported in the news that the load of traffic over the bridge exceeded the load that the designers had planned for. One thing that this event had in common with the Florida International University bridge collapse, is that both bridges were undergoing maintenance at the time of collapse. It seems like common sense that traffic should be halted during maintenance just to err on the side of caution. It turns out that in the case of the FIU collapse, cracks had been much worse than first reported and that a design flaw may have been responsible.
     
  15. Aug 19, 2018 #14

    CWatters

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    Picture and comment in the UK papers today includes discussion around the cable stays which are steel encased in concrete. One picture shows quite a lot of rust staining of the concrete stays near the top where they meet the towers. Comment says the concrete makes it hard to inspect the steel for rust. Apparently the stays on several towers had been reinforced in this area but not on the one that collapsed. This is also the area most likely to be hit by lightening.

    This could be nothing to do with the cause. I understand they were also working on the foundations of at least one tower.
     
  16. Sep 1, 2018 #15
    The reports on the collapse gave two pieces of information:
    1. They were doing maintenance work on the bridge at the time
    2. The collapse happened during an intense rain storm.

    These two together lead to a very prosaic but plausible sugestion:

    Bridge maintenance often includes the mainenance/replacement of the rubber bridge bearings. Temporary supports must be provided while this is done. Is it possible that the temporary supports were in the process of being secured when the rain squall hit, that some aspect had not been finalised but the workmen doing the job dropped their tools and made a dash for shelter. The rest, as they say would be history. Dropping a main support like that even a mere few inches would be enough to collapse the bridge.
     
  17. Sep 3, 2018 #16

    jedishrfu

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    While speculation is a natural consequence of disasters such as this, we must remember that only the final analysis counts. I am reminded of the Infamous Tacoma Bridge collapse and how for decades afterward people described the collapse as a consequence of harmonic vibration.

    However more modern analysis revealed it to be something more insidious.

    https://motherboard.vice.com/en_us/article/kb78w3/the-myth-of-galloping-gertie
     
  18. Sep 4, 2018 #17

    Baluncore

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  19. Sep 4, 2018 #18

    jedishrfu

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  20. Sep 4, 2018 #19

    anorlunda

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    It is still very contentious. https://www.physicsforums.com/threads/expunging-myths-from-the-classrooom.849853/


    But apropos this topic, the TWA 800 case is very on point. There were many theories discussed online. The most popular one is that it was shot down by a missile (backed up with eyewitness accounts). The actual cause, empty fuel tank vapor explosion, was too mundane to make the list of speculations.
     
  21. Sep 4, 2018 #20
    one look at the footage and you can tell there wasn't enough rebar in the concrete having been on enough sites when solid structures are torn down the volume of steel easily exceeds whats exposed at the bridge after the collapse. I'd bet you dollars to donuts the contractors shorted the amount thinking once the concrete is poured no one will see it.its always possible someone called for less rebar at the design stage but I'd be surprised if that was the case

    tension cables inside the concrete is common in concrete highrise construction to adjust the floor so it stays as intended. but they also have all the steel to rely on.as a counter force the bridge looks extremely lacking in that respect.
     
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