4 ms·

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

by 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
- heimdall 8y ago
  Lightning Strike Energy == 1,000,000,000 Joules 1 Joule heats 1g water 0.24 C 1 L water == 100g 1 cu.meter water = 1000L Room Temp == 23 C Thus: (77/0.24) = 320.8 Joules raises 1g water from 23 C to 100 C (boiling). (1E9 Joules / 320.8 Joules) lightning strike with no losses along the way heats 3,116,883g of water. 3,116,883g of water == 31,168 L of water == 31 cu.meters of water. This is a block of water 1m x 3m x 10m. Steam volume is 1600x liquid water volume. So even if we say that 90% of the energy is lost in the transfer, that's still 3 cubic meters of water that flash-boils into steam, quite possibly causing damage to the bridge. So: perhaps unlikely, but quite possible. Edit: 3,116,883g of water == 3,117 L of water == 3 cu.meters of water. Damn math errors, always creeping in. Still unlikely, still possible.
  - jakewins 8y ago
    Indeed. Lightning does this to trees all the time, there's a lot of crazy videos on YouTube of lightning causing trees to explode. https://en.wikipedia.org/wiki/Exploding_tree#Lightning https://en.wikipedia.org/wiki/Exploding_tree#Lightning
    - astrodust 8y ago
      Trees have relatively high resistance so they absorb a lot of energy. The lower the resistance, the lower the impact.
  - silvestrov 8y ago
    3,116,883g water is 3,117 liters and not 31,168 liters: http://m.wolframalpha.com/input/?i=3%2C116%2C883g+water+in+liter http://m.wolframalpha.com/input/?i=3%2C116%2C883g+water+in+l...
  - UnFleshedOne 8y ago
    1L of water is 1000g, then you need additional 2261 joules per gram to evaporate. So 1E9j will evaporate 384 liters of water, so 0.384 cubic meters (unless I lost a degree of magnitude here or there myself :)).
    - 8y ago
deleted 8y ago
[deleted]

by lqet 8y ago

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
heimdall 8y ago
Lightning Strike Energy == 1,000,000,000 Joules 1 Joule heats 1g water 0.24 C 1 L water == 100g 1 cu.meter water = 1000L Room Temp == 23 C Thus: (77/0.24) = 320.8 Joules raises 1g water from 23 C to 100 C (boiling). (1E9 Joules / 320.8 Joules) lightning strike with no losses along the way heats 3,116,883g of water. 3,116,883g of water == 31,168 L of water == 31 cu.meters of water. This is a block of water 1m x 3m x 10m. Steam volume is 1600x liquid water volume. So even if we say that 90% of the energy is lost in the transfer, that's still 3 cubic meters of water that flash-boils into steam, quite possibly causing damage to the bridge. So: perhaps unlikely, but quite possible. Edit: 3,116,883g of water == 3,117 L of water == 3 cu.meters of water. Damn math errors, always creeping in. Still unlikely, still possible.
- jakewins 8y ago
  Indeed. Lightning does this to trees all the time, there's a lot of crazy videos on YouTube of lightning causing trees to explode. https://en.wikipedia.org/wiki/Exploding_tree#Lightning https://en.wikipedia.org/wiki/Exploding_tree#Lightning
  - astrodust 8y ago
    Trees have relatively high resistance so they absorb a lot of energy. The lower the resistance, the lower the impact.
- silvestrov 8y ago
  3,116,883g water is 3,117 liters and not 31,168 liters: http://m.wolframalpha.com/input/?i=3%2C116%2C883g+water+in+liter http://m.wolframalpha.com/input/?i=3%2C116%2C883g+water+in+l...
- UnFleshedOne 8y ago
  1L of water is 1000g, then you need additional 2261 joules per gram to evaporate. So 1E9j will evaporate 384 liters of water, so 0.384 cubic meters (unless I lost a degree of magnitude here or there myself :)).
  - 8y ago

deleted 8y ago

[deleted]