OT: Italian bridge collapse

Global warming? Corona Virus? EU? Angle grinder? Not enough car body filler? Probably built by someone who believes in unicorn farts and pixie dust and Cant Do Sums.

A simple ?Don?t know? would have sufficed.

Tim

Really depends on why the first one came off. Its unlikely to just be due to the end of one deck section breaking off so it no longer sits on its pier.

Some kind of domino effect where one collapsing span pushed over the next??

Remember high alumina cement/concrete? Could be another of these.

No foundations to speak of? Built over a void or watercourse? Brian

Actually I remember once a small bridge was built using railway lines along the whole length as a support and one section gave way and of course this made the whole thing try to pivot on the central support cracking the concrete and it fell to bits. Luckily this particular bridge I'm describing was at a theme park and not in use at the time. Brian

Perhaps the concrete was full of body-sized voids.

More likely someone can do the sums and reckons cement is a bit on the expenive side compared with ballast.

One possibility is that it was supported on pre-stressed concrete beams, with tensioning wires running the whole length of the bridge. If they snapped, all the beams would have lost strength together.

Try telling that to the 'Climate Change' advocates...

When the Genoa Bride collapsed it was due a suspension cable snapping. The would unbalance the load on the supporting tower which would probably collapse taking out the deck section on the other side. Like dominoes/

In that case the safety checks were no longer done by their equivalent of the Highways Agency, but by a division of the company that owned tehbridge.

Exactly. Once one bit goes it may well be leaning on one or both of its piers (which were relatively tall and thin, with no bracing). There may be low-friction expansion joints at these supports too.

Good point!

Umm. It looks to me - the piers are still standing - as though the banks and supports *moved apart*. Once one span goes the load on the pier is unbalanced enough to allow it to shift a little and the next one goes,

Subsidence or a minor earthquake?

Anyway it needs a full engineering investigation and speculation at this point is amusing, but pointless.

Having found a couple fo pictures of the brdige re-collapse, I suspect a similar "knock-on" effect.

The carriageway decking is flat and thin, supported by shallow arches underneath. The space between the arches and decking above the piers has a number of columns to support the decking. A shallow arch exerts sideways force where it meets an abutment. Where two arches meet, say at the top of pier these forces are in balance, so the structure is stable. But if one arch collapses this balance is destroyed and the other arch could then push its end off the top of the pier causing it to collapes and so on...

yes. Whether an arch failed because the abutments had moved and it slipped off its perch or whether it failed because it had a structural flaw, the end result is the same. They all go.

Traditional multi arch masonry bridges have more substantial piers

Cf Clare Bridge in Cambridge which has stayed up despite its foundations shifting years ago.

Mafia concrete !.

Italy needs a lot of bridges because of its geography. There was a huge building boom after WW2, and many were not built as well as they could be, and now they are all getting to end-of-life, not helped by Italies regular economic problems and changes of government.

Like the A4 elevated sections in West London which I think had similar construction methods. Needed a lot of strengthening not too long ago.

Those suspension cables were coated in shuttred concrete too, allowing water to gradually get inside and corrode the steel.

And I always thought concrete was supposed to be used in compression, not tension ?. The architect thought it was an innovative design at the time.