101–110 of 116 posts
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You could have said the same thing about a guy trying to build a Mars colony...
AS someone who wants to go to Mars, anyone trying to sell you investment shares in a colonization effort is a scammer.
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If you do that, though, then all of your support structures the whole way through need to allow the tube to move inside of them. The tube is supposed to be supported every 100 feet or so (if I remember correctly) so that means that the last pylon has to be at least 500 feet from the station and that the tube has to be able to slide inside the support. I suspect that you'd see a lot of wear on the tube that's sliding…
I think that there are a lot of options for reducing friction wear. My first thought would be to put wheels between the tube an its supports (attached to the supports, not the tube).
So now you have wheels, bearings, preload springs, hinges, travel arms, etc. Instead of a big piece of plate that is welded to the tube and bolted to the foundation you're talking about a big apparatus with moving parts and precision bearings. The plate and welding might cost $500 per. The other might cost $20k apiece. A person can buy a lot of rebar and concrete and forms and whatnot for $20k.
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Thank you for the additional info. I am skeptical merely because they were quite hand-wavy about temperature accommodations, and it certainly is/was simplistic to think that ALL thermal movements can be accommodated for only at stations. (Especially if it's a direct and exclusive SF-LA route) Yes, the cross-sectional properties of the tube are going to be phenomenal, but I've always operated under the assumption that…
If you're dealing with bridges or buildings then you're right of course, you don't stress anything and you just let the stress dissipate through various movements. But thermal stresses are very small, for "normal" steel it's 13e-6 per degree C. If you figure that the temperature variations in CA aren't going to be more than say 40C (and that's probably too much) then you're looking at 520e-6 or basically 5e-4. As far…
ΔL=αΔtL; ΔL/L=αΔt; ϵ=ΔL/L; ϵ=αΔt; E=f/ϵ; f=ϵ/E; so f=αΔtE
ΔL = change in length due to temperature
L = restrained length
f = stress that arises due to full restraint
E = Young’s modulus
ϵ= strain
α= coefficient of linear thermal expansion
Using AASHTO numbers for structural steel:
f= 6.5x10^-6 (1/F)* 100 F * 29000 ksi = 18.85 ksi
That's a big chunk of the elastic 50 ksi range, and it's greater than a good portion of the allowable ranges from the table on page 41 of this PDF [1]. As you might already seem to know, AASHTO doesn't consider temperature loading for fatigue limit states, and in the Strength limit states it considers the force effects to be halved. (Though the displacement effects are multiplied by 1.2) Regardless, fully restraining these things at their ends doesn't seem like a good idea. Am I missing something in what you're talking about? Yes, the strain is low but fatigue generally works in terms of stresses.
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oh, that 600 million dollar per mile tunnel? not a great use of transportation dollars, think of how many EV buses they could buy, which on the whole buses tend to go where people want and do it more often than light rail which not only costs a fortune to build but maintain as well
I won't defend that project specifically because I know nothing about it, but I would like to offer a couple of comments: As a passenger, I have always found the experience of riding rail to be far superior to riding a bus for a lot of reasons including but not limited to speed and comfort. A train generally has much higher capacity than buses, and if well utilised, a lower operating cost per passenger. An ideal tran…
Earlier quoted context omitted.
I think that there are a lot of options for reducing friction wear. My first thought would be to put wheels between the tube an its supports (attached to the supports, not the tube).
You're increasing the cost a lot there because the wheels need to be on bearings because you've going to have to hold the tube with some amount of preload. You can't just let it rest on the wheels, the wheels have to be pressed onto the tube at all times because the vehicle is moving very fast and any kind of minute deviation up or down will result in substantial forces between the tube and the vehicle which have to…
If that is too complicated, just put in replaceable slide plates. More regular maintenance, but fewer moving parts.
Earlier quoted context omitted.
I won't defend that project specifically because I know nothing about it, but I would like to offer a couple of comments: As a passenger, I have always found the experience of riding rail to be far superior to riding a bus for a lot of reasons including but not limited to speed and comfort. A train generally has much higher capacity than buses, and if well utilised, a lower operating cost per passenger. An ideal tran…
When traveling from Seattle to LA, Greyhound buses are better than Amtrak trains for several reasons: faster, cheaper, easier to book, and less risk of Civil Asset Forfeiture.
Earlier quoted context omitted.
If you're dealing with bridges or buildings then you're right of course, you don't stress anything and you just let the stress dissipate through various movements. But thermal stresses are very small, for "normal" steel it's 13e-6 per degree C. If you figure that the temperature variations in CA aren't going to be more than say 40C (and that's probably too much) then you're looking at 520e-6 or basically 5e-4. As far…
Excuse my arcane units, but it is what I am familiar with: ΔL=αΔtL; ΔL/L=αΔt; ϵ=ΔL/L; ϵ=αΔt; E=f/ϵ; f=ϵ/E; so f=αΔtE ΔL = change in length due to temperature L = restrained length f = stress that arises due to full restraint E = Young’s modulus ϵ= strain α= coefficient of linear thermal expansion Using AASHTO numbers for structural steel: f= 6.5x10^-6 (1/F)* 100 F * 29000 ksi = 18.85 ksi That's a big chunk of the ela…
You might also be able to get some nice double-whammy effects from using something like a514 since it's corrosion resistant, has a higher elastic yield, and may well have a reduced thermal expansion coefficient. If you increase the strength and decrease the expansion at the same time then instead of blowing 40% of your "budget" on thermal it might only be 10%. And since you're covering such a large range of climates you might be able to rate every 10 or 20 miles of loop based on the climatic averages in that region instead of looking at the absolute min and absolute max for the whole thing. It might add a few extra weeks of design but make things a lot more feasible.
Earlier quoted context omitted.
Thank you for the additional info. I am skeptical merely because they were quite hand-wavy about temperature accommodations, and it certainly is/was simplistic to think that ALL thermal movements can be accommodated for only at stations. (Especially if it's a direct and exclusive SF-LA route) Yes, the cross-sectional properties of the tube are going to be phenomenal, but I've always operated under the assumption that…
If you're dealing with bridges or buildings then you're right of course, you don't stress anything and you just let the stress dissipate through various movements. But thermal stresses are very small, for "normal" steel it's 13e-6 per degree C. If you figure that the temperature variations in CA aren't going to be more than say 40C (and that's probably too much) then you're looking at 520e-6 or basically 5e-4. As far…
[1]http://www.matweb.com/search/datasheet.aspx?matguid=3f2ce033...
> The problem with traveling in an evacuated tube is, if you lose the vacuum in the tube, everybody in the tube will crash Wouldn't that be a "crash" into a gradually rising air preassure? Something like a smooth deacceleration.
I would not call it gradually rising. Pods would be moving at huge speeds and then hit viscuos fluid (compared with vacuum) It would be like hitting a wall. Pod should be constructed like supersonic jet to avoid crash.
I'm clearly missing something important because otherwise somebody would have built this already, but instead of using the fans for levitation as proposed, why not keep using the magnets? I'm imagining a tube with (8?) magnets equally-spaced around the perimeter so that the carriage inside automatically stays centered in the tube. We already know how to toggle the magnets to produce forward motion (see maglev trains)…