Friday, November 20, 2009

60> Prestressed Concrete Track for PRT and Other Automated Transit

One concept worth considering is making track from prestressed concrete. I’m not sure how it would work for the inner city or spans with a lot of curves or branches, but it might be a good candidate for freeway medians.

The groove on top and the corresponding hole in the support structure is for electrical or communication cables, and is meant to be covered by a metal cap. One might be tempted to question whether it is really feasible to cast such a shape. Actually it is really excellent, because by piping steam through a collapsible inner form, the concrete can be caused to set much more quickly. Beams can, in this manner, be removable within hours, allowing multiple castings per day.

The picture above shows the various rubber-mounted running surfaces associated with the previously shown designs. In a situation such as a high-speed longer distance application, not only would the rubber be unneeded, (concrete absorbs sound which, in freeway median applications, wouldn’t be and issue anyway) but most of the steel itself could be dispensed with, as well.
In applications with lots of stations and curves and branches it is easy to imagine a track in terms of a profile that serves all of those needs. For the duration of long, straight runs, however, the metal “fins” used in switching need not be present. Furthermore, larger wheels are probably in order for higher speeds, as suggested in post 56. Therefore the running surfaces normally used for the smaller low speed guide wheels should be removed or recessed, so that the small guide wheels don’t spin. In fact, I’m not sure that any of the steel shown is needed.
Without any buried utilities to prevent more closely spaced support posts, this might be a very cost effective way to handle the commuter market and reduce freeway traffic.

By the way, it occurs to me that most readers, even those with some engineering instincts, would be intimidated by the thought of trying to learn a new program, especially a 3D modeling program. Well the folks at Google are no fools, and they wouldn’t get into the 3D software business if they didn’t have something pretty special.

Here is a chair that I drew in under 3 minutes, following this YouTube tutorial. Try it. It’s fun!


cmfseattle said...

nice work. you could also incorporate Einar Svenson's Urbanaut long spans design.

Anonymous said...

Hi - it's me, the **real** Anonymous.

Pre-stressed concrete? Blech!

One of the best things about Ed Anderson's design is that it isnt made from pre-stressed concrete.

Dan said...

Dan The Blogger Responds-

Hi cmf..
Can’t do it, not without a legal war chest.
This guy’s got quite a minefield of patents on not just his V shaped support but on many other aspects of monorail track. Unfortunately, monorail track patents arguably include PRT.

I, personally, am amazed at the stuff he got away with patenting. Like that V support. It is obviously a take-off on arch bridge design. Take a Roman aqueduct, assume modern materials, (this means you can stretch it) take out the non-essential mass to make a more open structure, and you have his V. Obvious design evolution is not supposed to be patentable. And that is not all. He could probably argue infringement on the stuff I have pictured in this post, because he managed to land the absurdly vague terminology “recess” and “protrusion” in defining what can’t be done in regards to how the rails and supports connect. In other words, no male/female joinery between the rails and the supports, if it is for a monorail/PRT. It’s mind boggling. It is specifically written that nothing obvious is supposed to be patentable.

Anonymous, I am forced to assume that you are not an imposter. So…(I am casting a skeptical eye on your post) Thank you for the scientific analysis… NOT!

Blech? I would remind you that I was talking about a cheap way to get somewhere in freeway medians. (As a first point) Secondly, Anderson’s (most elegant) design is based on intricately cut and welded pipe, like a crane boom. (curved joining cuts in a curved material) It is much more complex and presumably much more expensive. It would be well worth the effort if the longest, most visually unobtrusive spans with a minimal footprint are the order, but in the median of a freeway? I say, “Spend the money on an extra PRT lane. There’s nothing pretty about traffic!..” But that’s just me, on one of these days when I let the exclamation marks fly.

I must say though, it does raise an interesting question. We have all seen our share of raised concrete highways. What would the same type of construction look like if the projected weight load were to be cut by 80%? Maybe the resultant dimensions would have a lot less “blech” factor. Thanks for posting, gentlemen.

cmfseattle said...

Are you talking about patent 6,571,717 (Svensson)? looks like the "recess" and "protrusion" terms refer to the columns and pedestals, not the beams themselves. Also, he cites Anderson's patent 4,665,830, "Guide construction and method of installation."

Starting on p.10 of the skyloop era rebuttal, there's a reference to the Millenium Force rollercoaster, which used m/f joinery in 2000, three years before Svensson's Y patent was granted. (after glancing at the wheels that coaster uses, i'm curious about the maintenance schedule, considering the 90mph speeds).

"My guideway is capable of higher speeds than are likely to be economically justifiable.

Dan said...

I think you’re right. That’s not the patent, though. Svensson lists them on his site. I think it was rail support/column connection, although I’m not sure what all he has slipped in, because he puts a lot of non-dependant claims in, and each needs to be examined separately. I really don’t have time to revisit it.

As for the roller coaster, I would only note that the wheels support very little vehicle weight, save for some moments of high G-forces. The bearings also have frequent opportunities to cool down. The wheels, not requiring traction, can be made of a very longwearing, hard material. Sound is not much of an issue either. I have always been troubled by the small wheel issue when translated into PRT, especially for higher speeds.

Anderson’s track design is certainly capable of supporting high speeds.

afransen said...

Hi Dan, I posted an o/t comment in 58, but I'll repeat it here:

"I believe blogger has a feature that shows 'Recent Comments' in the sidebar, making it easier to notice comments on older threads, that might be handy for both you and your readers."

cmfseattle said...

re: small wheels&high speed: you're probably aware that Unimodal (a.k.a. SkyTran) say they'll use Inductrak. you might not be aware that they've been making a lot of progress, lately. they're working with NASA at Ames and they have a bigger vehicle design.

i always figured all those copper coils would be too expensive. maybe not? they're also building a test track.

Dan said...

60- Dan the Blogger Responds-
Thanks afransen. Your contribution has been publicly noted and is much appreciated
Thanks also to you cmfseattle. Waiting for anything to happen on the Unimodal site has been like watching paint dry. I wonder if the new design is ADA compliant.It is worth noting that the Wikipedia entree has recently changed for "inductrack" to more fully express its attributes.(great game,this Wikipedia, eh?)
Nonetheless I was going to sing it's praises anyway. It is very cool technology. I certainly would not want to make "smart" systems be non-compliant with their dimensional requirments at this stage, especially since I believe in including a higher speed, longer haul aspect. Do note, however, that Inductrack, by itself, does not propel the vehicle. Its major drawback would seem to be that it requires a linear motor as well as it's inherent costs, what with the "in-track" coils and all. These costs are not trivial, but not out of line with road costs; The problem is that there is no way to divert road funds to something like PRT at the moment. The funds are paid for by gasoline taxes and are earmarked for gas burning vehicle infrastructure. This forces a bare-bones model which excludes systems like this - At least until someone yells loud enough. Ah-HEM..!(Dan the Blogger clears his voice)

Anonymous said...

Hi Dan,

Just how scientific do I have to be to deplore the butt-ugliness of pre-stressed concrete.

They don't call the architecture "brutalism" for nothing, ya know.

And I don't let you off the hook for proposing these things be installed on freeway medians. What's the logic there - "Already ugly, no need to change that"?

The strongest popular argument against PRT is - "I dont want ugly elevated track running in front of my house". Let's do what we can to avoid giving the Luddites something they can legitimately point to.

Dan said...

60> Dan The Blogger Responds-
Point well taken, Anonymous. The reason I faulted the “science” of your comment is this: Concrete can be made into virtually any shape. It can make sculptures, boats, kitchen counters. It can have any finish, be any color. Therefore it is not immediately obvious how it can be automatically labeled as ugly. Prestressing simply gives it the ability to be made into thin forms that would ordinarily break, such as a long, unsupported beam. (Or graceful, willowy shapes.) If you want to see butt ugly, check YouTube for monorails. There you will see some very ugly steel box-beam track. Anyway, I suppose I am guilty of the architectural “brutalism” you refer to, for similar reasons that most concrete is ugly. I was just in a hurry, and designed what people would expect. I drew the same blocky shaped structural forms you object to, and, in retrospect, that’s not good PRT advertising. Anyway, don’t blame the material, blame the architects and the factors that inhibit them from pushing the envelope. These days steel can be cheaply flame cut and welded into imaginative shapes, so concrete forms could be very complex.

cmfseattle said...

freeways aren't likely to disappear very soon; at least, not during the 50-year service life of most guideways. so concrete support posts make sense, anyway.

been sick for a few days and found some great SWE stuff in the waybackmachine. anderson had written about using an arch, but i didn't know an illustration existed.
T2 and its Biz (page 15) could work just as well for suspended, and made of concrete.

i'd been looking for this hi-res pic of the first prototype skyweb express vehicle. just ahead of the rear wheels appears to be a hinge, maybe? but maybe not, since the upper structure isn't hinged...

anyway, check my math/assumptions on this? they spec'd a 36-foot min turning radius. for a 40-foot radius turn downtown: (40(2*3.14))/4 = ~65 feet of curved guideway between support posts?

they were so close. so much good info, so little time.

cmfseattle said...

swe prototype

Dan said...

Dan The Blogger got momentarily confused - cmf, at first I couldn't understand your work. I was trying to get where you came up with the 2 and the 4, and why you wanted 3.14 to derive support spacing. I now presume you mean to get the circumference by multiplying the radius by 2 then by 3.14. Then you get the length of a quarter turn segment by dividing by 4. (62.8) My question is what relation does any of this have to where or how this arc is supported? It could have one or ten supports regardless of the length of the curve. I think there would be serious problems if they did try to make the turn unsupported. The weight of track and vehicles would be off-centered by up to 12 ft., creating enormous twisting forces (with 31 ft. of leverage) on the track and supports.
Nice pic. That piece of track (not the dolly) shows the pipe/truss construction. Very stiff, very expensive. Needed? debatable.

cmfseattle said...

0:52, 1/4-circle curve over street, posts on sidewalks
0:59, 1/4-circle curve over street, posts in street

pp. 18-32
chapter 10