Hyperloop Gets Test Track in California

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 you don't try to resist thermal movements, regardless of the strength of the cross-section. You let them dissipate and design for the deflection (e.g., at the bearings and abutments), rather than the stress (buckling/tensile) in the beam. If we start allowing stress to develop in the superstructure tube, I can't imagine what the cyclic fatigue impacts of that temperature stress will be. (Maybe it's not significant...)

I am no rail expert (though I am a civil/structural guy), but even continuous welded rail isn't always continuous for hundreds of miles. [1] I think that there are two factors at play: continuity in the maglev/rail structures, and continuity in the superstructure/tube. I do not know what maglev devices look like, but if they do look like traditional rail, then agreed that a CWR solution seems to be the way to go. That being said, no matter how stiff the tube is, it too will have to accommodate thermal movement. My gut reaction is to call everything tube related simply supported, allow for (6.5x10^-6x100ft.x100deg = 0.065 feet) ~= 0.75" of expansion or contraction at each pier, and surround this expansion zone with a metal sleeve of 2"+ greater diameter than the main tube. Simply supported, multi-span structures are a well-studied problem. Adding in the continuity of the rail/maglev structures are what make it hairy, IMO, and the interplay between seismic considerations and thermal considerations becomes important. As far as I can see, it's very important for the maglev structures to be continuous to ensure for smoothness and speed of the ride.

For example, given that you make the superstructure spans simply supported, you have these nearly perfect "mass-on-a-stick" seismic models with well defined, and relatively short periods. Then, you have much longer continuous sections of rail/maglev equipment that contain releases on a far fewer number of span segments. These will have much longer periods of vibration. Maybe I'm stretching here, but the connections between the maglev/rail and superstructure seem like a place that is rife with potential for failure and stress during a seismic event. (I would not want a life-safety issue being my most prominent failure point.)

[1] http://boards.straightdope.com/sdmb/showthread.php?t=471152

This is not Musks project, this is a collective of unpaid academics backed by a kickstarter knockoff and a PR firm in El Segundo

"Now, the company Hyperloop Transportation Technologies Inc. (which is not affiliated with Musk or Tesla) "

Musk is building his own "Separately, Musk has said he plans to build his own 5-mile test track, likely in Texas, for companies and students to test out potential Hyperloop designs."

They are going to do what they did to my friends project. Parade the techies around, get it funded, and then "lose" half the money "he 5-mile test track is estimated to cost about $100 million, which Hyperloop Transportation Technologies hopes to pay for with its initial public offering (IPO) later this year, according to Navigant's blog. "

And what the heck is navigent?

Land while probably an inevitable hot topic, is not actually what would classify as a problem for a project that if sees full scale deployment will most surely have government backing thanks to eminent domain. Yes, the project will still be expensive, but any land owner that tries to be a hold out in selling isn't going to prevent the project.

They will presumably be building this out in the middle of nowhere in CA, not in a downtown urban core. But it is helpful to be in driving distance to a metropolis with a high degree of excellent engineering talent.

People from out of state assume everything in CA is nuts expensive but you have to remember the state is also full of farmland, forests and deserts.

The engineering to do a 5 mile section is pretty straightforward. It's only 5 miles long (25000 feet) and around 250 joints.

1. Giant foundations and just handle the thermal stress by not letting anything move

2. Figure out the slip joints really well to soak up the ~125 feet of travel and still hold a good vacuum

3. Figure them out OK and just install extra vacuum pumps since there are only ~250 joints

4. Try out some/all of these options on 500 feet of tube in parallel to see how it all performs and don't make a final decision on the whole 5 miles until you have real cost numbers

The other thing I'll mention is that you don't need the steel to be continuous in order to hold a vacuum. You need the inside face of the tube to be smooth in order to not jerk around the vehicles, but all the sealing could be done on the outside with clamp-on seals. If the average continuous tube piece is 100 feet long and the max thermal expansion is 0.5% then you only need a half-inch gap between the tube pieces.

If your air bearings are say 3 feet long each and divided into 10 sections internally which are fed through orifices so that no one section can rob all the pressurized air flow then you're never going to lose more than 10% of your bearing force and you should be able to glide right over these 1/2" gaps with no problems. And if there are some problems a few accumulators (plain air tanks or pressurized bladders) inline with the supply lines would probably increase the momentary recharge capabilities enough to negate the problem.

700mph is 1000 feet per second or 12 inches per millisecond. That means a 1/2" gap is crossed in just 40 microseconds or so.