Elevated Bridge B/C

[bob3443]

an A frame bridge is a bridge that has beams going directly from the loading point to the base(you don't need a horizontal beam going across on the top, or a much shorter one)
this is what an A frame bridge looks like http://www.bridge-masters.com/photos/954.jpg
it does meet specifications for division B

Actually you cannot build an A frame bridge because the tension member that is required across the bottom of the A is not legal (it won't clear the clearance block). Without that bottom tension member the legs of the A have to take a large bending force that would make them very heavy. 3 and 4 years ago the tension member on the bottom was legal for bridges, as well as with tower for the past two years, and the weights of the most competitve bridges were extremely low (just over 3 grams and just under 4 grams for 05 and 06 Nationals respectively). I don't see how those weights would be possible this year if using only wood and glue.

i'm not talking about a bridge exactly like that, of course you have to change it so it fits the rules, but you can get a pointed tip (sort of) so the horizontal beam on top is shorter, (lighter and probably stronger)

[frontlineballer1]

Well heres my bridge boys, (and girls) tell me what you think it weighs and holds i've got states tomorrow, and i know what it will get. ill post videos and pictures for you guys afterwards because my team is dead awful and can't make it to nationals. i wish we could since last year i wouldve placed in the medals for both boomilever and Wright stuff. . anyways just let me know what you think it will get. woever is closest i will tell in private some secrets and techniques to it. P.S. there are some key pieces i left off when showing you guys so you cant just copy it


i pulled the picture because i dont want anyone to be able to copy it anymore. if you got the design down in the past day that great for you. you will still have fun figuring out what i changed to make it significantly better.
just have fun with it.

[Mike4192]

Use http://imageshack.us/ to upload the image, then post the direct link.

[SLM]

... anyways just let me know what you think it will get.

Assuming that you have used medium density balsa, my guess is that the bridge weighs about 12 grams, and it will hold about 12 kg.

Good luck!

[SLM]

Anyone have a prediction? ]

Clearly, you have spend a lot of time building the bridge, it looks nice.

My prediction: It will fail due to excessive bending in the mid part of the bridge. The long top compression member will fail first followed by some of the diagonal members in the mid section, and the long tension member. I don't think the bridge will be able to handle the entire 15 kg. I say it will fail before the load reaches 12 kg.

[andrewwski]

Is one of the "key pieces" part of the legs?

If not, that's going to slip outward pretty easily. Legs look very weak.

[jazzy009]

Well heres my bridge boys, (and girls) tell me what you think it weighs and holds i've got states tomorrow, and i know what it will get. ill post videos and pictures for you guys afterwards because my team is dead awful and can't make it to nationals. i wish we could since last year i wouldve placed in the medals for both boomilever and Wright stuff. . anyways just let me know what you think it will get. woever is closest i will tell in private some secrets and techniques to it. P.S. there are some key pieces i left off when showing you guys so you cant just copy it

that was a very interesting bridge, ive never seen anything like it, its so...modern? or at the very least different, i dont know, its very amusing though. im glad you built this, at regionals every bridge looked like the ones in the SO summer camp pictures...lame.
I guess at 10g (pretty nice), that would hold 11kg. i'd love to hear it held all 15, but i dont think those legs could take it. sorry your team cant send you to nats, i doubt ill be going to, but we have a shot once all the building events are solid (worked for 12 hours today, no school ). maybe there should be a national tournament with the 1st place state event winners...thatd be pretty insane.

[nejanimb]

Good luck Aia - something tells me you shouldn't have too much trouble, at least not with this event. I'll be interested to hear results when you return.

[Balsa Man]

Good luck, Aia; there is some very nice work there, and some neat design concepts.

I hope better, but my guess is , oh, I'll say 10.9k. Most likely failure mode does look like buckling in the long top compression pieces - in the vertical plane. Again, good luck

We have regionals today - my son is going in with a bit under 15 gr (depends on humidity- its going to be damp today); tested to a little over 13, should hold full; the Gods of Balsa willing- will report.

Len Joeris
Fort Collins, CO

[bob3443]

if some of the "key pieces" are truly the "key" pieces, then i say it might hold all the weight, and adding the "key" pieces on, i'd say it might be around 14 grams?
so 14grams holds all the weight is my guess...