Not sure if this is the right forum, but i figured this might be an appropriate place to ask regardless.

I'm taking an engineering class and our current project is to build a model bridge using: paper, elmers glue, 2x36" dowels, scotch tape and sewing thread. I've already developed an idea on how to construct the actual bridge, (I've come up with a sort of upside-down cable-stayed bridge that should work fairly well) but the problem I'm having difficulty with is the fact that the bridge needs to span a gap of 36", and the dowels that I'm using are also only 36".

So, totse, could anyone tell me how, or at least give me an idea, of how to extend this bridge using only the materials listed above, so that it will be supported on both sides of the gap, and also be able to support a somewhat heavy load?

Thanks in advance,
Zev

Use the two dowels to build a Wide Upside-down V that will support a deck hanging from cables. Once you have a strong way to hold this V up you can used tightly-rolled paper to make new "dowels" that can be used to build a strong deck and good "holders" fro the V. Attention needs to be paid to the balance of the V and could be accomplished with some wider supports at the base of the dowels of the V.

Ask if you need a rudimentary drawing.

RDP

Ask if you need a rudimentary drawing.

RDP


I think i have an idea of what you mean, and if its what i think then it sounds like a promising idea, but I would definitely appreciate that drawing nevertheless

When I did this we weren't allowed to use tape or thread. My bridge was the best in class it held up 12 pounds. I threw away all my plans it was 4 years ago.

It looked like this,

_______
WWWWW
_________


horrible picture.

I'd go for a conventional truss bridge.

http://en.wikipedia.org/wiki/Truss_bridge

Paper, when you spread glue on it and roll it up tightly, can function as the braces. I'm hoping you are allowed scissors or a knife?

Also lemme guess, you've gotten to play with the West Point Bridge Design software?

I think i have an idea of what you mean, and if its what i think then it sounds like a promising idea, but I would definitely appreciate that drawing nevertheless

http://i100.photobucket.com/albums/m22/RDProgrammer/bridge.jpg

Obviously build a strong joint system where the dowels meet. You can cross them as I have done here or make them meet at an exact point. If you cross them you can make a tight point with thread, if they meet you must make a solid cradle for them to sit or snug into.

RDP

A truss bridge is what I built.

You would be lucky if you are using bridge software. I only got 3 sheets of Keuffel & Esser Paper.

He might use that engineering (*bad-um tish* Possibly only Ytter will get the joke) game where you more or less have to build the most structurally sound bridges possible, for the engine and carriages (a.k.a choo-choo train) to cross. An addictive challenge, especially when you've got a huge gap to span, no piers allowed, and a heavy as hell train to cross it.

@Thread Starter:


Box truss FTW.

1) Your lecturers/teachers/whoever will be looking out for creative use of logic. So you should make it original, really, but with an obviously logical decision process. Don't expect it to be a masterpiece, you're there to learn this stuff after all.

2) If you want to create, you need to understand, and something you should definitely learn straight off the bat is about compressive and tensile forces. An extremely important topic for things that span, it's about way more than just the properties of materials. It's about the bridge itself as a one piece unit. Know about exploiting the equalised core, know about deformations. Reading up on bracing would be good too, for obvious reasons! And then there's Hookes law, and live/dead loads - including wind loads (oh the horror!!!). Learn yourself up on these.

3) That said, this diagram on the Wiki link Ytter posted is more or less what I think you should construct:
http://en.wikipedia.org/wiki/Image:Parts_of_a_truss_bridge.svg

I think the criteria may mean this is one of your best bets anyway, even if it has been done a million times before. It's a million times proven.

Note: I'm not sure about the terminology used there though - Stringer/s is a term used only in stairs AFAIK, and 'floor beams' should be called bearers or LB (load bearing) joists, or struts.

4) If you're able to, and allowed piers/supports of any kind, follow a design like this (also from Ytter's link):
http://en.wikipedia.org/wiki/Image:Hampden_Bridge_Wagga_design.jpg

Unbelievabley I actually know this particular bridge in real life, we go fishing together. Nah, I went there to study it and it's a very good bridge to base a design off - if you could.


*It's hard to describe what kind of course I am studying, and man people get the wrong idea. It won't make me to be a type of engineer or anything of the sort, but (for some reason, obvious to me but too long winded to put in this post) a substantial of it is technically engineering.

So I'm not an engineer nor studying to be one. The guys above possibly know a lot more than me (but I don't know how much they know, you see). Take their advice, it's good! Not a big fan of RD's idea there though, but that's purely subjective.



I have no time to make any of my post eloquent or more helpful, it's a fucken mess, a disaster of disarray, a nightmare. But I have to go.

I proposed the design of the leaning-Y because he said he wanted some of the dowel on both sides of the gap. The dowels are not longer than the gap so whatever secured the bridge to the "cliff edge" would have to be very well built.

RDP

How are you supposed to do the nodes?

http://i100.photobucket.com/albums/m22/RDProgrammer/bridge.jpg

Obviously build a strong joint system where the dowels meet. You can cross them as I have done here or make them meet at an exact point. If you cross them you can make a tight point with thread, if they meet you must make a solid cradle for them to sit or snug into.

RDP

This is exactly what i was thinking, and i believe it will be my design (obviously tweaked a bit as construction progresses)


Also lemme guess, you've gotten to play with the West Point Bridge Design software?

No, I have not. It wasn't even mentioned, for that matter




@Kwinnie - there was too much in your post to quote/reply to, but i still appreciate it and will take it into consideration

Try braiding the thread into rope. You could get really complicated and think if you like. That would make it much stronger.

- Tom

That West Point Bridge Design was pretty cool..

Here are all of the bookmarks I saved when I was going through that class. Some may be helpful, some may not, some may be completely random... They're from a few years ago so some may not work.
Bridge Basics - A Spotter's Guide to Bridge Design (http://pghbridges.com/basics.htm)
Bridge Building Contest Home Page (http://www.iit.edu/%7Ehsbridge/database/search.cgi/:/public/index)
Bridge Building (http://www.42explore.com/bridge.htm)
Bridge Types - Truss (http://www.matsuo-bridge.co.jp/english/bridges/basics/truss.shtm)
BridgeBuilder-Game.com - The ultimate bridge building games website (http://www.bridgebuilder-game.com/) BridgeBuilder-Game.com - (http://www.bridgebuilder-game.com/)
Bridges (http://www.brantacan.co.uk/bridges.htm)
Geometry of Bridge Construction (http://www.faculty.fairfield.edu/jmac/rs/bridges.htm)
http--www.chroniclogic (http://www.chroniclogic.com/)
http--www.jhu.edu-~virtlab-bridge-truss (http://www.jhu.edu/%7Evirtlab/bridge/truss.htm)
NOVA Online Super Bridge (http://www.pbs.org/wgbh/nova/bridge/)
Physics Balsa Bridge Building Contest balsabridge.com ...next contest May 2 2006 (http://www.balsabridge.com/)
The BridgeSite - Fun and Learning (http://www.bridgesite.com/funand.htm)
Truss Types (http://www.maplevalleytruss.com/config.htm)