STAii
Dave, can you please give us first an introduction about yourself, your relation to designing, and how you reached those designs ?
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 traveled 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 traveled 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 learned 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 realized 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 learned 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 realize 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!
Dave
Consider it spam? No way! Thanks for replying.
No big deal in making high buildings? - I'd say earthquakes and high winds.
Russ,
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"
The axial force inside a bridge around the world is a thin-walled pressure vessel problem and quite simple to calculate.
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?
Dave
Thanks for your comments on my site by the way. Sounds like you've got a good grasp of the concept!