Since this thread is about trains, or long train tracks to be more accurate, have you ever wondered just how long a train can get? 
Well here it is, according to this video. I’m tempted to believe it, too.
It takes over 10 minutes for this train to go by, and it looks like it’s going about 40-50 mph. :eek:
Seems that we do something similar in the UK. For some strange reason I could not quite understand, we have lengths of line cut into 216 metre pieces - they actually are produced in 108 metre pieces and two welded together prior to movement to the site.
I could well imagine that the line itself is delivered some time prior to fitting in place.
http://www.therailengineer.com/2012/11/05/highly-organised-high-output/
[QUOTE=Habeed]
Doesn’t the welding process use thermite and a mold to make a really smooth join?
The reason I ask is that can you be 100% certain it’s all one piece and not smaller sections?
[/QUOTE]
I’ve seen enormously long rail being delivered to the work site. As mentioned above, it’s surprisingly flexible, and as for the compound stiffness of transporting multiple pieces, IIRC, they’d carry about six pieces at a time. The rail delivery train moved rather slowly, and the huge lengths of steel made otherworldly twitching noises.
Thermite welding makes a fairly rough joint. It just takes a lot of grinding to make it smooth.
Yeah, I guess you’re right - maybe it’s simpler than my gut feels it ought to be - it seems like it ought to be almost an insane idea to me; “How are we going to get these long bits of metal to site” / “Oh, we’ll just bend them around every corner”
That’s certainly not always the case. Take a look at the video posted by JBDivmstr upthread - something like 30 to 40 pieces on that train, I’d say.
When they were replacing the old freight line with rail for the new DART rail in Richardson, Texas about 20 years ago, there was a large stack of rail piled up just south of Campbell Road, which I drove by every day, so I decided to measure it with my car’s odometer.
The rails were approximately 1/4 mile long - that’s about 1300 feet, or 400 meters! I have always wished that I had seem them bring the rails in, how they got around corners, how many they could carry at a time, how they unloaded them off the cars, etc.
But about bending around the corners - the ground the rails were lying on wasn’t perfectly flat, and the rails followed the contours of the ground like they were wet pieces of spaghetti.
A friend and I had a discussion about whether he could lift one end of one of these rails - he thought he could, I thought he couldn’t - but we never got around to testing it.
I think people are overthinking and underthinking this at the same time and it is because of looking at it from different scales. A short length of rail track does look very rigid but only because it is short in relation to its width and because it is thich for a human. In terms of lengths of hundreds of meters a rail is just a big piano wire.
Take a short steel nail of 2 or 3 mm diameter. You would say it is very rigid. Impossible to bend with your hands. Now take a steel knitting needle of the same diameter but 30 cm long and you can definitely bend it with a large radius of a few meters. No problem. If the wire were long enough you could easily make a full circle around your house and the wire would spring back .
So what really counts is the ratio between the diameter of the wire and the radius of curvature. Suppose a 1 mm steel wire can be curved with a radius of 1 m, then the equivalent for a 10 cm rail is to be curved with a radius of 100 m. Which in terms of railroad tracks is not too much at all.
And the equivalent of a 10 cm rail track 400 m long (ratio 1:4000) is a 1 mm wire 4 m long. Take a 5 cm length of 1 mm wire and it seems extremely rigid, more so to an insect, but take 4 m and it cannot hold horizontal even its own weight.
Notice how close the track sleepers are. And once you have some bad or unsupported sleepers you will see the track flex very visibly when the train goes over it.
In terms of lengths of hundreds of meters a rail is just a big piano wire. If you had to build a large bridge with rails then the only way to do it is to build a suspension bridge and use the rails as supporting wires. You cannot use rails as beams for significant spans because they would flex way too much. You either use them as suspension wires or you build complex trusses.
The short answer is “no”. Not in any significant, observable way. Even with several people. I suppose if you used a micrometer you might be able to observe a tiny deflection.
The forces acting on rails, beams and other structural components are orders of magnitude larger than human scale. Which is one reason we need tools. Try tightning a nut with your fingers and see what I mean.
WOW, that is 1 impressive video. It more than answers the question about transporting long rails. And it is going around a curve. Thank you JB.
Brings about 2 more questions to me however.
#1
Just how do they load that thing?
#2
If that rail track is 1/2 mile in length, then how do they deal with the expansion and contraction when it heats and cools? That is when it is laid on the rail bed. Gotta wonder how many inches that piece of steel moves and the joint to the next rail.
Tracks are mostly under tension. If laid on colder days they are either stretched mechanically or heated along their length before welding
It is just a highly unusual way of delivering something that is notionally straight - that’s all - things that are bendy are normally coiled, rolled or folded - things that are straight are usually kept straight in transit - it’s just an exception to what we normally expect to see.
Come to think about it rail could be coiled in coils, say, 500 m in diameter. Each coil turn would be about a mile long. I guess it is not practical on land.
As a transportation student, I agree. Railroads have very gradual curves. By definition, no curved segment delivered would have a greater curve than the existing rail. The rail certainly wouldn’t deflect enough to permanently deform, at least at low speeds, which is why straight segments wouldn’t be harmed by the curves.
I think you are mistaken if you think rail is manufactured “curved” (with radius X) or straight. I think rail is manufactured straight and curved when it is laid down.