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Comment by laurencerowe | Hacker News Reader

Wouldn't the gap simply be the result of loss of tension after the weld broke? Metal expands in the heat (about 1cm per degree C per km). Weather shows it got down to around 0C in Córdoba last night while the summer record is around 47C so one would expect a fairly large gap once tension is released.

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That's not the way stuff like this is built nowadays. Meaning the thermal expansion and shrinkage of rails is considered and accounted for(or should).

Thus things like these are integrated:

https://en.wikipedia.org/wiki/Breather_switch

As I understand it breather switches are used rarely in high speed rail systems. The ride on Spanish high speed trains is very smooth. At 300km/h (5km per minute) you’d notice going over a breather switch. It’d be like taking Amtrak’s Acela.

The gap looks about 50cm which is maybe 1.5km of contraction from installation tension.

I disagree. Though I've never ridden Acela, I did Intercity Express at 330kph. Since I've been rail fannig in my youth, I still look out for rail-related stuff. Even if it's 'only infrastructure'. Meaning I notice that stuff in pictures in reports about building/opening new HSR track. No matter where. Seems like they are mandatory. You just don't notice them, even when looking out of the window onto the other track, because it's all just a blur. Need to be on an overpass, and looking down onto where they are, for instance, or from the side, during construction or maintenance, watching how the machines operate, and wondering about what they are doing there. Because it's an interruption :-)

Some better pictures:

https://www.eisenbahn.gerhard-obermayr.com/produzenten/vae/s...

https://slabtrackaustria.com/our-technology/red/

https://www.voestalpine.com/railway-systems/en/products/rail...

https://upload.wikimedia.org/wikipedia/commons/7/7d/Oelzetal...

https://upload.wikimedia.org/wikipedia/commons/b/bf/Schienen...

https://cmi-promex.com/wp-content/uploads/2023/06/CurvedRail...

https://cmi-promex.com/wp-content/uploads/2023/06/Sound-Tran...

https://www.hsrail.org/wp-content/uploads/2024/06/HSR_Track_...

Your pictures show breather switches installed at a tunnel portal where they are necessary to handle the large differences in temperature and on what looks like various bridges which can be subject to their own thermal expansion. But at least as I understand it there's normally no need for them on continuously welded rail otherwise.

We will know once the report is public. In Poland, they explicitly left C14 to make sure everybody understands who did it.

C4?

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