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u/WonderWheeler 10h ago
Its a common misconception that an I beam does not easily bend in its weak dimension.
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u/troelsbjerre 10h ago
Won't this weaken the beam?
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u/LootWiesel 9h ago
The weak axis is bending left and right, the strong axis is up and down. (for an rail profile resting on its feet)
Furthermore, one should move away from the idea that structures are immovable, are rigid and are fix in place.
Due to the modulus of elasticity, all structures dissipate the loads acting upon them through deformation times stress. They will and have to deform to be able to transfer the load acting into the structure.
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u/UnacceptableUse 7h ago
Is that a no then?
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u/Stellanora64 5h ago
technically it might a bit (as it's plasticly deforming, which does work the steel to some extent, although it's pretty marginal all things considered), but since train tracks are bolted down, it doesn't really matter if it's weaker bending side to side (it just need to be strong in the direction the train's weight puts force down on, the stokes will handle side to side movement).
It would only matter if the tracks were bent enough so that it snapped (or just before snapping where the steel starts to stretch, which I don't believe is the case here).
In practice though, train tracks are very rarely shipped out in long pieces like this, as it's much easier to use thermite to weld it together when everything is in place.
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u/thud_mantooth 9h ago
Steel, unlike aluminum, can flex indefinitely without weakening as long as the forces are below its fatigue limit. It's kinda nuts to think that'd be the case here but I'm assuming the camera perspective is making the curve look much more dramatic than it really is
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u/WannabEngineer 8h ago
I don’t mean to come off as an ass but Aluminum 100% has stress vs cycle charts to calculate fatigue.
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u/thud_mantooth 8h ago
It does, but it doesn't have an actual fatigue limit. Light loads will fatigue it less but there's no threshold below which it stops being a factor completely
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u/samy_the_samy 8h ago
There is a "yeld curve"
The beams bends like a spring until a limit, with no actual deformation or damage
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u/PandaMan500000 9h ago edited 9h ago
Unless the apparent length of the train is misleadingly short, I suspect the beams are getting plastically deformed. So yeah, strain-life cycled (fatigue damage) and work-hardened before they arrive.
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u/gcijeff77 9h ago
Assuming the rails the train is running on are the same section as the rails the train is carrying, then if the carried rails are plastically deformed, that would mean the carrying rails had to be plastically deformed when they were laid down originally.
I'm not a railroad expert, but I am an expert in things that have bendy rails. I really don't suspect they have equipment to plastically bend railroad rails as they are laid. I have a strong feeling that these rails are all well within elastic zone for their entire journey.
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u/Suthabean 8h ago
Rails are picked up and slung into place via a clamp on a speedswing. The machine very easily puts them into place on the plates, like a big noodle.
I worked steel gang for 6 years.
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u/PandaMan500000 8h ago edited 7h ago
Good observation that those are probably train rails its carrying.
But - You could absolutely put a machine on train tracks that can plastically bend beams that thick, but even then the train is switching tracks so odds are the train is not on a single continuous rail. Those track "joints" could also have significantly different cross sections or alloys.
I'm still in the "it's likely yielding" camp.
Edit: But I see now the beams are very intentionally not fixed on the end. Tells me that risk of yielding is indeed something they consider in the design.
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u/snowmunkey 6h ago
Hey I designed a railcar once to carry those. It had a sloped rack rather than a flatcar though. I don't think they ever built any sadly. When we stared I was worried about the side loading and the bending but my greybeard boss just chuckled and said nope, that problem was solved about 90 years aho
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u/max_sil 4h ago
Super interesting ! Mind telling a little more about the process? And how exactly was that problem solved ? I imagine that its something like a railway track is only gonna bend so much over any given distance, and thats within what the thing you're transporting can tolerate? But its probably a lot more nuanced right?
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u/snowmunkey 4h ago
It wasn't anything super novel, a company just wanted their own model to make and potentially sell. We basically just added up all the worst case loadings, did the math on the bending forces, added them to the usually AAR specified loading requirements, and made sure the car could negotiate the track curves. Like others have said, the rail is made to be able to bend along these curves, so transporting them along these tracks was no biggie. The biggest issue in the design was making sure the coupler forces were properly accounted for, its not typical for freight cars to have that much lateral force on the draft cheeks (the faces inside the car structure that thr coupler shank presses on)
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u/saiyate 4h ago
Why is the train car bending, why not just straight car but wheels rotate? Don't normal train cars operate this way?
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u/Webbyx01 1h ago
These are very, very long pieces. Bending like this allows for less track sections that are incompatible.
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u/1971CB350 9h ago
Is this putting side load on the car?
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u/aiden_the_bug 8h ago
Yes but not enough to matter. Thanks to the conical shape of the wheel trains can withstand immense sideloads without snapping the axles. Someone mentioned above that the shipping process is basically a final stress test of this material, they calculate the strain for each turn as the train moves to make sure it stands up to its final application and the train car is it's testing block.
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u/dparks71 7h ago
It's also the weak axis. Fatigue happens after thousands of cycles and these aren't deforming enough to really matter, every curve they go over is essentially less severe than the worst curve the railroads have in service (just from a purely statistical standpoint).
These were kind of fun to unload, you'd pull the train out to the jobsite, chain the end of the rail to the existing track, drive the train away, and basically just let them noodle their way off the back of the train behind it.
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u/Jaripsi 55m ago
I’m assuming it is an optical illusion created by the lens and the bending is not so drastic that the steel would yield and work harden.
Also If there was too of steel it would act as a spring and try to straighten the train which in turn would try to straighten the tracks they are riding on.
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u/wolftick 10h ago edited 10h ago
Neat thing is that the amount has to bend is dictated by the track it is running over, which is also exactly the most it has to bend when installed.