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Earthquake bridges and towers (new)

  1. Mar 19, 2003 #1
    Bridge to 7 km and towers to 3.5 km. (plus other lightweight designs) at: http://groups.msn.com/DavesBridgesandTowers

    My last thread was just starting to get interesting when the new forum took over! For anyone who missed the final messages, I have recently added more drawings to the site that are an exaggerated view of my webbing designs. I think that you'll agree that it is the obvious next step if we want to go further and higher.
    The design, normally only two to three layers of webbing, would be used for communications towers, earthquqke proofing of tall buildings, stadium and aircraft hangar type roofing and larger bridges.
    I claim that the designs are the lightest/strongest and most economicaol possible ever.
    I am also seeking help with computer analysis and animation if anyone is interested.
    Regards, Dave
  2. jcsd
  3. Mar 19, 2003 #2
    According to an article that i read (not long time ago) on www.popsci.com , they say there is no big deal in making high buildings.
    They say the problem of high buildings is not building them, the problem is maintaining them, and providing services in them, and finally the cost :smile:.
    Architect say they are able to do a building more than 1 KM long NOW if you provide money to them :smile:.

    Dave, can you please give us first an introduction about yourself, your relation to designing, and how you reached those designs ?


    (Dave, if you consider this post as somehow spamming your topic, tell me and i will delete it).
  4. Mar 19, 2003 #3


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    Staff: Mentor

    Hmm.... Its bAAAAAAAAAAAAaaaaaaaaaaaaack. Ok. Certainly bridges can be longer than they are now. Its mostly a question of money but only up to a point. There is a limit on how big they can be and be able to support themselves: the finite strength of steel (or titanium if you have a lot of money).

    If you want to go back to the "bridge around the world" thing, I had a good post up right before the site turned over:

    The axial force inside a bridge around the world is a thin-walled pressure vessel problem and quite simple to calculate. More in a few minutes (after work).
  5. Mar 19, 2003 #4

    OK but there's not a real lot to tell.
    I grew up on a farm not far from here. Moved to West Wyalong at age 12. Dropped out of high school at 14. (turbulant teens). Became a bricklayer at 17 and travelled around a bit (mainly the east coast of Aus') Returned to Griffith (100 mls from here) for about 10 years. Learnt building, carpentry and joinery. Started up a business as a joinery in nearby Narrandera. Split with first wife (she got the lot) and travelled around some more before returning to WW where I have remained for the past 13 or so years.
    I'm 48 years (young). A bit of a rebel, with girlfriend and four daughters (3 from previous relationship) 8 to 18.
    About 10 years ago, living on a farm property 10 miles away, needed a shade area on the northern side of the house. The simplest way would have been to put up a few log posts and rails, then attach shade cloth, but thought I'd be a bit creative and make it out of an arched pvc tube, so that it would be able to swivel back on to the foof during winter months.
    Two things I remember from childhood:
    1) I remember one particular TV program on ABC when I was about 12 yo. - Showed what was known about different methods of strengthening steel (hollow tubing with a hollow sphere centre or honeycomb profile) and truss designs. - At the end of the show they concluded by saying "All that is needed now is for someone to put it all together"
    2) When I was around 25 yo, don't remember the program, someone (assume it was an engineer) said, "Design has reached its peak....The only way we will be able to go further is for a lighter, stronger more composite material be developed"
    I understood that all there was to know about spanning was already covered. I had never attempted any type of spanning other than solid timber or steel purlins. - But for some reason thought that the span (14 metres with a 4 metre rise) using only 2" pvc tubing and some type of wiring system, it would be a simple task. Not so! (is now though)
    I tried several ways of tying the wire to the tubing without success. Then I tried running one wire from point 1 to 3,5,7 etc' and the second wire from 2,4,6 etc'. - There was some improvement but not enough! - Then I clamped the two wires together where they crossed over. The strength was, or so I thought, spectacular! - Now I was getting somewhere!
    That was when I started learning! - I abandoned the project and started to build smaller models using 18 mm pvc and 1 mm piano wire. - With the (above) crossover/clamp method, I found that when you placed a compression member (my hand) between the tubing and clamped wires, the strength improved again. - No good for flat spans though! - So included another wire, which became the bottom chord. In fact, it was exactly what is known as a simple "K" type webbing truss. - So all I'd learnt was what was already known!
    I then built an 18 metre model using only 1" steel tube, struts and cable. - It stood up OK but was very floppy. - I'd earlier on played with a double crossover model (total of three wires. One at points 1,4,7. Two at points 2,5,8 and three at 3,6,9) but didn't really think much of it. - Considered adding a second layer of webbing to provide more lift, but understood (and was reassured several times later) that it was too complicated....Too much labour and materials etc'.
    I was "stumped" ....Didn't know where to go from there.... but kept on coming back to the two layer idea. - It was the only way to rid the floppiness, particularly if the span needed to be bigger! - So I kept at it until I understood it!
    After a while it became even more obvious and understandable. - It was embarrasingly simple! - Surely when an engineer seen my design it would be even more obvious to them, so I contacted a few. - The most common reply was, "It's ALL been done before!" - Nothing new! - That's when I realised that engineers DIDN'T UNDERSTAND IT AT ALL! ....All they knew was how each component reacts against another! ....I was assured though that ....They were the experts. I'd need to do 20 to 30 years of engineering before I know what they know!
    The way I see it: - I don't hold any qualifications so.... What would I know!
    The difference: - I learnt from scratch. I was self taught, very determined (and curious). It was "hands on" all the way. Ignorance at first, and now after 10 years, total understanding. (still not sure about the endless bridge though!)
    What now? - I've given up trying to get help from the "experts" and have aimed my understanding at younger students in the belief that they are more open minded and able to think out of the "box", less critical. - It is the same for any profession. The longer you have been there, and the more you learn about what is already known, the harder it is to think out of the box. - Then someone comes along, without qualifications, and tries to tell you that you've got it all wrong! - I was the same! - But I am now able to listen with an open mind - because I've been there!
    I realise now that I should have exaggerated the drawings a long time ago, but didn't then for the earlier reasons (too complicated and too much materials).
    I wouldn't even have a clue which engineers do what! - I've at least been getting replies on this forum though, so it is getting talked about. - So thanks everyone.
    Sorry if I rave on a bit, but the "experts" claim to be looking for new ideas....You try to tell them and they aren't the slightest bit interested! - Darned if you do, darned if you don't!
    That's my story anyways!

    Consider it spam? No way! Thanks for replying.
    No big deal in making high buildings? - I'd say earthquakes and high winds.

    Glad you're back!
    Yes, I was wondering about your last reply. I did manage to get a peek at it (unless there was a second reply) during changeover.... which took me totally by surprise! (I knew there were to be some changes, but thought the existing threads would all continue).
    When you say for longer bridges, it's mostly a question of money, I believe that with my own design, the economics (and easier understanding) will prove to be at least half the cost of present cable stayed/suspension type, which look very "precarious"
    Yes, if this is what I understand it to be, I believe that you will be able to demonstrate clearly....and there should be an easy way to physically test it! - Which is my aim overall.
    I once suggested on another forum that, if you could scale the bridge down to a thin walled cylinder and lower it into water to the related pressure, it would be a true demonstration. - I didn't get any feedback though. - Is this what you are saying?
    Thanks for your comments on my site by the way. Sounds like you've got a good grasp of the concept!
  6. Mar 19, 2003 #5


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    Staff: Mentor

    Ok, thin walled pressure vessels (now where did that damn link go.....) http://www.ae.su.oz.au/structures/mos/mosch09b.htm

    Ok, the reason it applies is what you have is a distributed load - in the pressure vessel its a fluid pressure, with your bridge its gravity. The key is that your bridge is circular and the vessel is circular (cylindrical). So the forces look exactly the same. Also note, that the equation is reversable - it works the same for positive and negative gage pressure.

    s = stress
    p = pressure
    r = radius
    t = thickness (vertical)

    s = p * r / (2 *t)

    Now here's what's beautiful about it:

    w = weight
    wd = weight density
    v = volume
    a = cross sectional area

    Since the pressure is just equal to the weight of a section divided by the (horizontal) cross sectional area, you get this:

    wd = w/v and p = w/a

    Combine the two and you get:

    p = v * wd / a Cancel v with a and you get

    p = t *wd

    Throw that into the axial stress equation and cancel thickness:

    s = wd * r / 2

    Simple and elegant.

    Now, the numbers:
    r = 2985 miles (approximate radius of earth)
    wd = .2836 lb/in^3 (weight density of steel)

    s = .2836 * 2985 *(5280*12) / 2 (converting to inches)

    s = 26,818,577 psi or 26,818 kip

    Now the compressive stress an object can sustain DOES depend on geometry (there are other equations for that), so there is no standard value for steel. Tensile yield stress though is on the order of 500 kip. Maximum compressive stress is LOWER.

    If you remember from the now dead thread, the equation is very similar to one someone derived for you except he lost the "2." Essentially though, he derived the thin-walled pressure vessel equation from scratch.
    Last edited: Mar 19, 2003
  7. Mar 20, 2003 #6
    Thanks russ,
    Is there a scaled down example you can give me? - Say steel, half the thickness of fax paper over a 10 metre radius (probably a lot more), and at what depth?
    Sorry, I don't understand the maths a bit better....My limit is circumference of a circle, area of a cylinder! - Calculate diagonals for square footings etc'.
    I'm sure the figures are right, but I need something to visualise. Don't bother though if it is too much trouble, as I am willing to accept that what you have all done is equal to a physical test. It was a very interesting topic though, and thanx for putting up with me! - especially Enigma. He put a lot of work into it!

    Still on the same subject (oh no, what am I doing!) I once saw a program about Mars....How they would be able to build a "Buckminster Fuller" type structure around the whole planet, due to the low gravity. - I think that Bucky (could have been someone else) also stated that the geodesic domes were unlimited to their size here. - To my understanding, say a dome spread over a 500 km radius.... The tubing would have to be only short lengths (many triangles) or else be very large diameter/larger triangles. - Therefore, would buckle easily....Don't know!
    Anyway, I agree that the bridge subject is dead and buried. Wonder though if it helped others understanding on other things?
    I hope my recent drawings have provided a better idea of what I have been trying to say about strengthening/webbing etc' ....Which were a result of the debate anyway. - So it wasn't a total waste!

    Any comments on the 3.5 km tower....Or 7 km bridge? - The tower I am absolutely certain about! Bridge....At least 4 km and far more economical than existing! - Very simple to build also! - Even on a 2 km span, would be half the cost of suspension bridges. What do you think? Does anyone see it the way I do?
  8. Mar 20, 2003 #7


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    Staff: Mentor

    Well, as I showed, thickness is irrelevant. But let me see if I can give you a scaled down example using an arbitrary thickness. I'll get back to you.
  9. Mar 24, 2003 #8


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    Staff: Mentor

    Ok, lets try steel one inch thick. And drop our bridge down to 10' in radius.

    p = wd * t so
    p = .2836 * 1 = .2836 psi

    Now, this is just a ratio. At 10' radius our scaled down bridge is:

    10 / (2985 * 5280) or .0000007345 times the size of the full sized bridge.

    So ratio up the pressure by the same amount.

    .236 / .0000007345 = 371,955 psi

    Water has a weight density of 62.4 lb/ft^3 or .03611 lb/in^3

    371,955 / .03611 = 10,300,609in or 858,384 feet under water. I think the max depth of the ocean is about 20,000 feet.
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