Distinct movement cluster evident on Carola bridge in Dresden prior to collapse | Hacker News Reader

Distinct movement cluster evident on Carola bridge in Dresden prior to collapse

newcivilengineer.com

18 pointseerikkivistik22 comments

I'm sure there is plenty of movement visible on all kinds of bridges. We also know that all bridges will fail eventually, so the real value is having a more or less exact prediction _when_ they will fail, not a "we totally saw that coming" after the fact.

> there is plenty of movement visible on all kinds of bridges

Sure, but "the movements in the cluster began to show an atypical pattern with diverging paths" does highlight that even though movements might be common for all bridges, the particular pattern they discovered for this bridge was uncommon.

Agree that the maximum value one could get from a process like that would be "When will this bridge fail?", but better than nothing, is to get a "This bridge looks like it will fail soon".

Besides, could manual human-driven inspections even be able to give a "more or less exact prediction of when a bridge fails"? If not, then at least a somewhat automated way of getting the same answer would be cheaper for local governments to run, and for the cases where it makes sense, send the human bridge inspectors there.

> a "we totally saw that coming" after the fact.

That's not the case, though. This isn't an "I told you so," like the 2022 Pittsburgh bridge collapse. (https://www.ntsb.gov/news/press-releases/Pages/NR20240221.as...)

The study ended 7 days before the collapse, and it only concluded that an on-site inspection is needed:

> Its findings revealed there were significant indicators present prior to the incident to suggest inspection/consultation with on-site engineers would have been necessary.

This is a random company selling everything from blockchain to big data analysis performing a retrospective analysis of satellite data over a certain period prior to the collapse. In other words it’s a puff piece to promote the capabilities of what sounds like a very dubious firm, not a report of a predictive study.

So they did survey it for over 3 years, had the data and said nothing and now they advertise their failings as a positive?

It is an after the fact survey done on historical satellite data. More data can be found here: https://newsletter.value.space/p/bridge-collapse-germany-aty...

It s a bit bizzare article but the fact we could detect similar failures is good. Not sure tho why anyone would use satelites for this. They could just use normal sensors that would give you way more precision.

https://www.encardio.com/blog/bridge-monitoring-sensors-type...

Captain Hindsight saved the universe. Again!

Seriously, I think if they can show in hindsight how this could have been predicted using satellite data, and then using this knowledge in future to save a few other bridges (and lives), it is quite a cool finding.

That is the goal.

Yeah, I'm baffled by the whole thing too.

- "According to a spokesperson from Dresden's Road and Civil Engineering Office, the bridge was frequently inspected"

Implies it frequently passed inspections–multiple, recent ones. How did the civil engineers make such an egregiously wrong call on this one? They didn't make enough alarm to even temporarily close it; it was a near-disaster,

- "The last tram crossed the span just 18 minutes before the collapse, dpa reported."

https://apnews.com/article/dresden-germany-bridge-collapse-c...

The German system is undoubtedly different to the American system - but [1] an American bridge that collapsed despite regular inspections might give you some idea of how this sort of thing can come about.

[1] https://practical.engineering/blog/2024/6/18/this-bridge-sho...

> Insurtech utilises technologies such as artificial intelligence, big data analytics, blockchain, and machine learning, to support the insurance industry.

What is this strange mismash of terms thrown around? I always assumed(limited liabilities) that machine-learning was a sub-set of artificial-intelligence.

> A distinct movement cluster on the western superstructure of the bridge of up to 23.50 mm per year [...] Additionally [...] from October 2022, the movements in the cluster began to show an atypical pattern with diverging paths

> Additional movement on the northern side of the bridge structure was also revealed, which could have indicated additional stress accumulation in the bridge’s western superstructure

So, the bridge was under stress and moving(breaking off?) slowly by few mm each year causing the eventual collapse? Was the movement due to the traffic over the bridge or also supported by the movement of water on the ground?

> It was also determined that bridge elements in the water, would raise the water level by around 30 to 50cm from the Carola Bridge to the level of the Waldschlösschen Bridge about 4.5km west of the Carola Bridge.

So, the collapsed and submersed debris from the bridge will raise the water levels by several inches having sone consequences for the Waldschlösschen bridge?

Can someone with more knowledge on such topics ELI5 me the overall things I quoted above?

> So, the bridge was under stress and moving(breaking off?) slowly by few mm each year causing the eventual collapse?

This is what it looks like from the data. The key here is "diverging paths", which means different parts of the bridge were moving in different directions, putting strain on it.

> which means different parts of the bridge were moving in different directions, putting strain on it.

Thanks! But how was this not noticed[1] by the maintenance and renovation works? I would assume, such patterns should show visible cracks or some symptoms beforehand.

[1] I know that, for a huge structure, a few mm movement is tough to even notice without major equipment and monitoring, but still I believe inspections are done frequently for structural changes and damages.

Not sure. Perhaps a further investigation by the authorities will reveal the reason.

A commercial venture can observe movements in the millimeter range from space? If this is true, I'm equally impressed as I'm terrified.

In some conditions, yes. You need a cluster of points which have good reflectivity and coherence properties to microwaves over some time (months to years). Manmade steel and concrete structures, like bridges, houses, dams, etc, usually work very well.

You can't measure their position to the millimeter range, but with some interferometry techniques you can measure their movement to the millimiter range, relative to close points. Some variation of https://www.sciencedirect.com/science/article/pii/S092427161... was likely used in that work, I've seen it done for many other structures (and I even tried to setup a pipeline for doing that for commercial customers, but in the end we didn't manage anybody to fund us).

You can probably get better measurements with an onsite survey, but using satellite data has the advantage that with a handful of satellites you can map an entire country once every one or two week, and after throwing some computing power at it you can theoretically monitor all the bridges and houses at once and get early predictors of possible problems.

These case studies give you a hint of what can be done: https://www.sarproz.com/case-studies/ (I'm not and never have been affiliated with that product, just linking some cool pages).

For a advanced course of physics, we had to analyze video image of tiny "balls" in a microscope and track their movement. We were able to track movements of 1/10 of a pixel fitting a function using the tones of grey. Even if a pixel is 10 meters, I think it's possible to track smaller changes assuming the bridge does not change the shape too much.

You absolutely can and it is true.

> [...]the movements in the cluster began to show an atypical pattern with diverging paths

What the heck does this mean?

> Insurtech utilises technologies such as artificial intelligence, big data analytics, blockchain, and machine learning, to support the insurance industry.

Holy buzzword soup, batman.

Why is this being upvoted? This is a meaningless article.

When I arrived at the blockchain part, I knew they wouldn't tell me how they'd done it. Looks like a PR dept wrote some fluff which got taken up by a magazine.

The worst part is how they present it as if they totally could have predicted it if they tried.

So this is done via InSAR (https://en.wikipedia.org/wiki/Interferometric_synthetic-aper...), leveraging ESA satellite data. Not sure on the buzzword bingo there.

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