Hyperloop Gets Test Track in California(news.yahoo.com) |
Hyperloop Gets Test Track in California(news.yahoo.com) |
[1] http://www.leancrew.com/all-this/2013/08/hyperloop/
Thermal effects on Maglev research: https://www.lib.utexas.edu/etd/d/2007/kimh10315/kimh10315.pd...
EDIT: Apologies for the negativity... I hope this reads as more of thoughtful criticism, rather than as being hypercritical.
Earthquakes require active dampening which defiantly increases costs, but a larger issue is how to cross fault lines as you need a very large turning radius so very long segments of track need to be able to move. AKA you can't do this: http://pubs.usgs.gov/fs/2003/fs014-03/pipeline.html Unless you’re willing to really slow down.
PS: Also of note, you are going to need safety exits on a fairly regular basis and some way to quickly add air to the pipe as people are not going to be able to walk hundreds of miles in case of an issue.
Successfully designing for earthquakes does not necessarily mean active damping. (That is, it is not "required" as you state.) Yes, many large structures use specially designed mass or viscous dampers for dynamic loading (Citigroup Building, NYC; Taipei 101; Millennium Bridge, London), but others are designed to fail safely such that life and structure are preserved to the greatest extent possible. Specifically for bridge structures, there is the notion of plastic hinging in visible locations. [2] This way, the failures can be identified and repaired before normal use resumes. Here are some relevant state DOT guidelines. [3]
[1] http://www.spacex.com/sites/spacex/files/hyperloop_alpha-201...
[2] https://en.wikipedia.org/wiki/Plastic_hinge
[3] http://www.dot.ca.gov/hq/esc/techpubs/manual/bridgemanuals/b...
If the car gets badly damaged, but the passenger stays alive, and the system can be fixed in a reasonable amount of time, then this is fine performance for a major earthquake event. High speed trains have similar performance in the same situation.
[1] https://en.wikipedia.org/wiki/Maglev#Operational_systems
You could also build segments with the intent of inducing displacements to study what's needed for seismic inputs.
The big problem with this is not the technology. It's land acquisition. As with high speed rail, you need a right of way that's straight or has very large radius turns. There are sections of I-5 that are straight enough, but high-speed travel between Bakersfield and Tracy isn't that useful. Tunnels can help, but are not cheap.
China is building high speed rail through urban areas on pylons. As with most elevated rail, the reality is much wider and more heavily built than the concept art. (China's maglev is a one-off demo; China's high speed rail system is huge.)
"The 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."
Run away, run far far away. They might as well do a kickstarter. Seriously, what sort of "business" is a 5 mile test track?
Lets say you charged $25 for a "5 minute ride on the hyperloop!" and you got 8 people in it, and you had perfect efficiency, and you ran non-stop for 10 hrs a day, 7 days a week then $100M is 414 days. And that isn't including the cost of running the ride in the first place. I guess I'll find out why they think I should think about investing in their S-1 but for right now, I am totally not seeing it.
* Invent something totaly new
* Test it on a small scale
* Get a lot of negative comments on HN
Wouldn't that be a "crash" into a gradually rising air preassure? Something like a smooth deacceleration.
Perhaps in the very unlikely event it ever rains again in California, water in the tube could be an issue, or lightning damage. That brings up the logical question of how many customers you'll have if none of them have any water to drink. Perhaps this would make more sense as a project under the Chicago Regional Transit Authority, or parallel to the existing Acela track on the coast.
1 atmosphere of pressure isn't going to suck in anything concrete, except maybe in dust format.
A slow leak that the high-vac pumps cannot deal with is a slow deceleration.
A massive crack will cause quite the stir in the tube. Think of a balloon. When you inflate a balloon you put, maybe, 1.1 atms more into it. This is about 1/10th that of the hyperloop system. You know how loud even a simple party balloon can be, and the forces that you deal with.
I don't really know how that alters what you've stated, if at all, but it didn't seem to be addressed, so I figured I would throw it out there.
If it actually had a test track, then most of the discussion in these comments could be obviated.
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). Could still use the partial-vacuum to keep drag down. And you remove the single-point failure mechanisms of the fans on the carriage and minor misalignment of tube segments.
This article will one day be featured in a museum exhibit on laughably divorced-from-reality bubblethink.
Just because it sounds hard and there are lots of challenges, don't give in to the nay sayers.
Hyperloop is a nerd dream and it doesn't have a chance at financial success. The fundamental problem has nothing to do with the technology, which appears amazing and viable. If anyone can overcome the few nagging engineering issues, Musk and Co are the ones to do it. No, it has to do with not having a viable market plan, suffering from very common delusional assumptions in business models that have fucked over railroad capitalists for well over 2 centuries now, including three major railroad bubbles (Railway Mania as well as the Panics of 1893 and 1873). [1]
The faulty assumption is that the viability of the railroad hinges on the ability to go from major city to major city as fast as possible. This is only partially true. Of course you want to be as fast as possible, but the worst possible way to be as fast as possible is to eliminate stops in smaller cities and towns, which is exactly what Hyperloop is planning on doing. Those small towns usually end up being the most prominent drivers of revenue, overshadowing the large-city-to-large-city revenue by an order of magnitude. Even the CHSRA business plan shows that their revenue model does not depend heavily on the SF<->LA passenger volume.
You can typically think of demand for travel in terms of cultural dependencies. I have a need for employment, therefore I travel to work. I have a need to visit family, therefore I travel to family. I have a need for tuna, therefore I travel to the wharf market. I have a need for a visa, therefore I travel to the embassy. These cultural dependencies result in a demand distribution for travel that roughly fits a power law profile. The demand for near travel (x > 0) is exponentially greater than further travel (y > x). It is not hard to speculate that the passenger miles travelled by Angelenos traveling to work outweighs the aggregate passenger miles travelled between Los Angeles to San Francisco on any given day...LA County's Metropolitan Transit Authority alone accounts for 5.4M passenger miles a day [2], approximately equivalent to 14,000 passengers traveling between SF and LA. More importantly, the larger the city, the more your cultural needs are met by your own city. If you live in Los Angeles, your probabilistic need to travel to San Francisco is much lower than someone from Fresno, because your needs are mostly met by Los Angeles. When I lived in Stockton, I travelled to Oakland or San Francisco almost on a weekly basis...but now that I live in Seattle, I travel outside of the Puget Sound region maybe 2-3 times per year.
In the very beginning, this faulty assumption was actually a safer assumption to make than it is today, due to the lack of airlines and automobiles. The railroad literally was the fastest way to get from city to city, with no exceptions. But now it isn't. Once you go over about 300 miles, a well timed trip by plane is often as fast or faster (a lot of people will say that 500 miles is the threshold of competitiveness, but travel market share peaks and then drops off after about 300 miles). Under 100 miles, the freedom of a car to leave without a schedule often makes cars faster. Any time you have competition, you lower your market share, with your comparative competitiveness determining how much market share you lose.
So this is how it has played out hundreds if not thousands of times in the history of railroads: 1) Some big city businessman sees a slow trip to a city that he commonly has to travel to. He sees a demand for faster transportation. He throws together a business plan that makes the correct assumption that City A has X people, City B has Y people, and a fast connection between them will yield Z% market share of the travel D demand between them. He figures that in order to get that fast travel time, he can only stop at the largest cities in between...or possibly no stops at all! He then looks up a similar city or railroad (lets say B & S railroad), looks at ridership figures, and tries to back into D, and then inflates the Z figure to reflect the fact that his railroad will be faster because there are fewer stops. Therefore his revenue model becomes X * 0.5D * Z * P + Y * 0.5D * Z * P (where P == ticket price) 2) He sells some stocks and bonds (or in the case of modern capitalism, lobbies for grants), and builds a railroad. From this article, it looks like this step is starting. 3) After a few months, he realizes his model is inaccurate. At this point, he will do one of two things: either advertise more or remove stops to make it faster, both of which exacerbate the cash flow problem. 4) After about a year, he is bankrupt. The bondholders reclaim as much as they can by selling the railroad to some other capitalist who will with high assurance do exactly the same thing, but with a greater chance of success due to a much lower investment. And thus plays out the railroad consolidation game.
In terms of the model, his failure was actually three failures multiplied together. 1) He assumed that the ridership of B & S railroad was primarily between termini. This meant his D figure was too low because he vastly underestimated the demand to and from the small intermediate cities. 2) He assumed that B & S ridership figures were rides at full terminus-to-terminus prices, therefore inflating P. 3) He assumed that D was a linear function of population, ignoring that the larger the city the lower the cultural need for travel, thereby inflating D. The only thing he got right was X and Y.
The practical implication of this is that if you want a successful, profit-maximizing railroad, you need to optimize the need for speed with the need to pick up passengers along the way. If you are a capitalist that cares about maximizing profit, this unfortunately means having a railroad that looks like a slow kludge, because it means making unglamourous stops in unglamourous towns. And it also means that technophile idealism puts you at a competitive disadvantage.
[1] for more information/history, this is a great writeup, with a couple chapters that clearly describe this delusion. It is very long, but amazingly interesting and worth reading outside of this reference for anyone interested in technocapitalism or bubble economics. http://www.dtc.umn.edu/~odlyzko/doc/hallucinations.pdf)
[2] http://www.apta.com/resources/statistics/Documents/FactBook/...
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.
http://upload.wikimedia.org/wikipedia/commons/thumb/9/9d/Com...
This company (Hyperloop Transportation Technologies) got no funding, Hyperloop Technologies did ($8.5m).(which is in reality a PR firm called jumpstarter pr in El Segundo)
They are hoping to raise the funding at IPO
"Now, the company Hyperloop Transportation Technologies Inc. (which is not affiliated with Musk or Tesla) has inked a deal with landowners in central California to build the world's first Hyperloop test track"
"The 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."
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.
http://2.bp.blogspot.com/-1LB4PjiDdgU/Ur_tPvwj5HI/AAAAAAAAAo...
http://en.m.wikipedia.org/wiki/Line_S1,_BCR
China opened 32 new high-speed rail routes in one day last December.
http://qz.com/308791/china-flexes-its-high-speed-rail-muscle...
By the time the hyperloop connects the 400 miles between SF and LA, China will have 30,000-40,000 miles of high-speed rail.
"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?
Of course it's different because there's a clear post-IPO acquisition market for biotechs. Not quite as clear who would buy Hyperloop if it's proven to work...
Since they aren't one of the big engineering infrastructure companies (Halliburton, Bechtel, Etc.) its unclear what they can do if they run into hiccups (like say nobody can fabricate the parts they need).
So do a $100M series A? Sure I could see that, a collection of billionaires wishing to bet on them making something that can work, but we should have trained people in the 90's to not buy stock in companies that have no hope of revenue in the forseeable future. (and say what you will of the recent Tech IPO's they have all had revenue)
[1] "Now, the company Hyperloop Transportation Technologies Inc. (which is not affiliated with Musk or Tesla) has inked a deal with landowners in central California to build the world's first Hyperloop test track"
Some day, scientists hope, the value of the monorail will be seen. That day, we expect to extend the rail line to other communities. Meanwhile, we just pulled a tunneling machine out of its boring hole, continue to expand the Link Light Rail system, and are developing various trolley-based solutions such as the ones in South Lake Union and First Hill.
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
If you have some thoughts on how that would work please share them. I'd like to learn.
I'm guessing (and I will know more when I read their S-1) that they build their test track, they prove out the concept, then win a contract to build a larger one from one of the states? So how far does that $100M get them? Does it get the 5-mile track built and operating? Looking at other complex projects, say the London Eye, which cost $100M in 1999. And it's just a Ferris wheel. I don't know of a 5 mile rail project that has cost less than about half a billion but I would certainly grant you that those tend to be bid on by cost+ contractors.
So I'm just trying to connect the dots on how they "go to market" as it were.
I doubt it will work, but it's not a stupid plan.
I think using this as a delivery system first, prove it out and increase safety as you go along is the way to go. It should be far cheaper to do it on physical goods first (hell you may even be able to skimp on the safety in some aspects), make lots of money transporting things and then work on a people version.
- For planes, there were 4,394 near-misses in 2012 [1]
- There were an estimated 5,419,000 automobile accidents in 2010, just in the US, resulting in 32,999 deaths [2]
- And the recent Amtrak train derailment, which could have been prevented (although why the prevention mechanism needs to be in the track, and not on the train itself seems strange). [3] There is also an estimated 2,280 collisions at public/private crossings resulting in 267 deaths in 2014. [4]
The question in my mind is whether the proposed Hyperloop system would be more prone to accident than our current systems of transit. I doubt our current means of transit would fare well under some of the proposed scenarios in the comments.
[1] - http://news.discovery.com/tech/airplane-near-misses-how-ofte...
[2] - http://en.wikipedia.org/wiki/List_of_motor_vehicle_deaths_in...
[3] - http://www.huffingtonpost.com/2015/05/13/derailed-amtrak-tra...
The Hyperloop, to put it generously, has a lot of "unanswered questions" and practical limitations. Just considering the safety (and escape) of this thing takes you into areas that raise legitimate concern.
I'm not going to discount it completely with aircraft still around and failing as badly as they fail, it might be workable, I just want to see some figures on how much it will cost Vs. Maglev (a technology already deemed too expensive to deploy on the medium to large scale), and more so how much it will cost to make it safe.
Would I love to go across the continental US in a few hours? Heck yeah. Will I be able to afford it if it has Concord's ticket price? Likely not, I'll fly.
It's a chicken-and-egg problem. New things are uncertain, uncertain things are risky, risky things aren't funded, thus new things stay new.
"This new technology is expensive because it's new!" is a tautology that gets us nowhere in terms of progress at a social level.
But don't you think you're failing to account for cultural dependencies that arise as a result of travel possibilities? Of different types of travel altogether?
For example, a 45 min subway commute is average in NYC [1]; as a result, going 30 min on the subway to meet someone who lives an hour away is not a big deal whatsoever. Since Metrocard costs don't vary by distance or time, and you have 8 million people used to lengthly amounts of subway travel, inter-city friends and relationships are more varied and spread out over space. [2]
If we assume that the Hyperloop is _not_ a railroad, or an airplane, and will have different types of time/distance payoffs, then we would have to assume a different form of demand curve altogether. For example: Japan's high speed trains -- and most importantly, their extreme reliability (like, to-the-minute) -- make long-distance commute a completely viable mode of transit. When high-speed trains are so reliable, you can have 9 minute transfer overlaps between two different trains going hundreds of kilometers, expanding range due to the UX, so to speak, of travel. It's qualitatively different than just a faster Amtrak or a slower plane.
[1] http://www.capitalnewyork.com/sites/default/files/Embargoed%... [2] http://observer.com/2015/05/the-social-commute-how-the-big-s...
I'm assuming you already acknowledge this, but successful marketing involves positioning to avoid competition and attempt monopoly on the market segment (It seems Thiel is the latest to rebrand this concept). Low-cost stops at minor intermediate cities is a competitive advantage that no airline would ever be able to compete with, as the costs of takeoff and landing are huge relative to the cost of the trip.
Major city termini > 300mi apart, however, is a huge competitive advantage for airlines. No matter how fast you get, you are always going to give up some market share to airlines on more marginal considerations like schedule flexibility, seat size/comfort, baggage limitations, etc. That is a huge and potentially very expensive rabbit hole for competition that a city-to-small-town transportation system can mostly ignore.
Probably in a few years, when the hyperloops are ready, owning a car won't be as usual as now, but you'll be able to pick a self driven one paying per mile or a fixed per monthly quota.
No.
> I thought we could get advance warning from P waves. (This doesn't work if you're in the epicenter, unfortunately.)
Yes, but the advance warning is on the order of seconds, not minutes (per Wikipedia, for deep, distant, large earthquakes, 60-90 seconds is possible, but that's still at most a minute and a half.)
Everyone's been hearing about Bertha and the tunnel calamity, but almost nobody's heard about the trolley that connects 6 neighborhoods, was installed in about 6 months, and it's already done.
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 transport system will use trains for the high traffic trunk routes and a tightly integrated bus system as feeders for the train line. It should never be expressed as an either/or proposition. Both are necessary.
Edit: I agree with you that the risk is very, very high. But, it at least gives a non-zero potential for investment return - which on that level is better than, say, Kickstarter.
Implies that they are not, and it is not true. Long range, high risk investments are available to any interested buyer.
Generally the challenge that comes up is that the SEC has set standards for someone to meet in order to be a "qualified" investor. Some people interpret those standards as a way of "keeping people out" of investing, but that is not the case. They are there for two reasons, one so that when those people lose all of their investment they aren't "damaged" and more importantly so that unscrupulous sales people cannot dupe people who are unable to distinguish risk for themselves into investing.
So I understand when a smart person who is chafing under the restriction of not being qualified from preventing them from a certain investment. But they have to realize that they are not the ones being protected. The elderly who are being promised a "guaranteed" 20% return on the last of their life savings by a boiler room broker, they are being protected.
Further, qualifying, is simply a matter of building up your portfolio to demonstrate you have the knowledge and presence of mind to make those decisions and if they go badly you knew the risks. The youngest person I've met who was a qualified investor was one pretty much right out of high school. He had started with $5,000 in a Charles Schwab account (his college fund) and moved it over to E-Trade when it was at $30,000 and was over a million about a year after he had graduated high school. He read a lot, developed a much deeper understanding of finance than I will probably ever have, and showed me just what was possible for someone determined to get there. Nearly every day there are stocks that move up by more than a few percent, and if you can anticipate that movement more often than not you can move a portfolio along.
And I would have no trouble whatsoever with these guys on a road show trying to drum up investment. And as I've said I'll read their S-1 with interest. I would not want them to do this raise on the general market because that opens up defenseless people to get hurt by folks who just want to push shares.
On the public market, the disclosure requirements are much higher, and you're more likely to find analysis, public articles and reports or other analysis you can buy. As far as I know, there's no qualified investor provision for buying stocks on the public market. In the end you can personally wish this company doesn't offer an IPO, but I don't think there's any systematic rule that prevents it as long as they file all the required disclosures and find a financial firm willing to do the administrative work of putting the shares on the public market. (Again though I'm no expert here... so it would be interesting to learn more.)
On the public market, one could class many tech companies in the long-term, high risk, show little to no profit category.
The disclosure requirements will, I believe, kill any chance HLT has for doing an IPO. I would worry if they were able to get past that hurdle.
My response was more for people who complain they can't invest in pre-ipo companies when they don't meet the qualified investor criteria.
I would respectfully disagree. The rail industry has figured out how to do Continuous Welded Rail (CWR) quite well, using the elasticity of steel.
http://blogs.agu.org/landslideblog/2011/03/08/distorted-rail...
Similarly the tube for the Hyperloop doesn't HAVE to free-float against its foundations. It might be easier or harder depending on various factors to work on expansion joints or doing the tube equivalent of CWR. You'd probably work on both to figure out which is easier in the long run.
Considering that it's a 9-11ft diameter tube with about 1" wall thickness, it's going to be pretty stiff, especially relative to traditional rails. The moment of inertia means that it should be very resistance to bending or buckling under compression and under tension steel is usually very good.
Given that there are going to be plenty of turns that the track has to make, I would look at doing a combination of two things:
1. Working towards a CWR style solution
2. Allow some movement so that the corners can take up the slack as the tube expands
The turns are very gradual and sweeping. But you could imagine that there's a virtual intersection between two straight portions that you determine by drawing lines from the straight portions until they meet. The actual turn will take place far from here, but it's instructive. So as the tube expands, the actual curve is going to move ever so slightly from the neutral position towards the virtual intersection. So long as there is enough room on the pylons to accommodate this, things will be pretty good. The tube will go from being curved 0.1 degrees per 100 feet to 0.105 degrees per 100 feet (or something like this) but this can be designed for and ensured that it doesn't cause the tube to buckle or collapse. It's engineering, not the utter unknown.
At their desired vacuum pressures, the steel doesn't need to be anything special, so I would love to see the mechanical engineering that goes into designing the 5 mile track's materials.
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.
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
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 as strain goes, that's not a terribly big number at less than 0.1% especially considering that most of the stress/strain graphs will go up to 10% or more and the first 1% are usually WELL within the linear elastic region. That means that you're talking about doing perhaps only using a few ksi of the steel's strength for the thermal effects.
Anyway, you don't need active dampening to keep the structure intact, but a 750mph vehicle suddenly needing to lift 10 feet in the air you’re going to need a lot of head room not to hit the top of the tube. Not to mention rapid left right displacement. Granted, cost/benifit let em die yada yada.
I suspect that you'd see a lot of wear on the tube that's sliding over the pylon supports as it might go through at least one if not several heating and cooling cycles daily. I could see two cycles if you've got side heating after dawn, midday shade under the solar panels, and then late afternoon heating after the solar panels stop casting a shadow over the tube. You might get another cycle if you have two parallel tubes with two parallel lines of solar panels above them.
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.
If that is too complicated, just put in replaceable slide plates. More regular maintenance, but fewer moving parts.
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.
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.
[1]http://www.matweb.com/search/datasheet.aspx?matguid=3f2ce033...
You can get a36 for about $1/lb in small quantities. You can get corten (a588) for about $2/lb in small quantities. But the a588 has a yield strength about 50% higher than the a36, so strength-for-strength it's a pretty decent deal.
If you need 1" of a36 then you're going to need only 2/3" of a588 so it's only 33% more expensive. Combine that with the weathering properties which can reduce your maintenance intervals substantially (this is the same steel they make sea containers out of) and your lifetime cost might well be lower.
Further since your tubes now weigh less you might be able to get away with either smaller pylons or greater pylon spacing, both of which might be advantageous.
So you're right that the strain is non-trivial but that's only if you pick basically the toughest, least strong steel available. It's pretty easy to go stronger and to not lose too much toughness and gain other desirable features such as corrosion resistance, and in the process make the strain less significant relative to the elastic region.
