Bridge Designs

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Bridge Designs

Postby brayden box » October 9th, 2015, 7:34 am

What kind of design works the best?
thread for bridge viewtopic.php?f=209&t=7816
Last edited by brayden box on October 9th, 2015, 10:21 am, edited 1 time in total.
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Re: Bridge Building 2016

Postby brayden box » October 9th, 2015, 7:37 am

Do you know a good design to use that's light?
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Re: Bridge Designs

Postby laidlawe18 » October 9th, 2015, 9:31 am

There is already a forum for Bridge Building. Please make new threads regarding bridge building in that forum.

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Re: Bridge Designs

Postby brayden box » October 9th, 2015, 10:22 am

Sorry. I think I did it right, the thread I mean.
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Re: Bridge Designs

Postby bernard » October 9th, 2015, 10:28 am

In response to your first post, I'll quote what I posted in another thread this year: viewtopic.php?f=209&t=7816&start=15#p280859
bernard wrote:
Daquan wrote:Has anyone found some successful ideas for the bridges?

If you're asking about design, there is no one best design. Some of the bridges that placed at nationals last year looked just like mine and others looked nothing like it. The best recommendation I can give is start with a design you like and think will do well (if you don't know what will do well, do some reading or look at pictures of bridges). Then test it, observe it as it is loaded and fails, then make more. Don't change a whole lot as you work towards a successful design or you might not know what's good. Students I've talked to who have done well in the event in the past have made many bridges.

Also, I've moved this topic to the Bridge Building forum.
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Re: Bridge Designs

Postby brayden box » October 9th, 2015, 12:14 pm

thanks for moving it. I forgot to put it in here.
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Re: Bridge Designs

Postby brayden box » October 9th, 2015, 12:14 pm

oh, and thanks for the advice. I did that, and I built a k-truss bridge. I held 42 pounds and wasn't even bowing! Only thing was, it weighed about 25 grams!
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Re: Bridge Designs

Postby SPP SciO » October 17th, 2015, 8:53 am

Curious: has anyone ever built or seen a single-piece bridge? A student suggested starting with a single block of balsa and creating a real fancy looking bridge through subtraction..

On one hand, I think it's really interesting, and not impossible- drills, coping saws, hours of careful sanding ... On the other hand, it's a significant investment of time and money - Any thoughts before setting some kids loose on this project?
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Re: Bridge Designs

Postby UnprunedShrub » October 17th, 2015, 9:08 am

SPP SciO wrote:Curious: has anyone ever built or seen a single-piece bridge? A student suggested starting with a single block of balsa and creating a real fancy looking bridge through subtraction..

On one hand, I think it's really interesting, and not impossible- drills, coping saws, hours of careful sanding ... On the other hand, it's a significant investment of time and money - Any thoughts before setting some kids loose on this project?


Wouldn't that kind of bridge be really weak? In a normal bridge, the grain is parallel to each piece, but in a single piece bridge the grain would be all messed up and could even be perpendicular to the member and would split easily in those locations. It would probably also waste a lot of wood and it would be really hard to make a bunch of these bridges. If you really want to go through this idea, I would suggest that you laser cut your bridge instead of trying to do it by hand.
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Re: Bridge Designs

Postby Less_Incidence » October 17th, 2015, 10:00 am

UnprunedShrub wrote:Wouldn't that kind of bridge be really weak? In a normal bridge, the grain is parallel to each piece, but in a single piece bridge the grain would be all messed up and could even be perpendicular to the member and would split easily in those locations. It would probably also waste a lot of wood and it would be really hard to make a bunch of these bridges. If you really want to go through this idea, I would suggest that you laser cut your bridge instead of trying to do it by hand.


I would be inclined to agree with that statement. I can understand the reasoning with regard to the lack of glue joints, but given that a properly-made glue joint is tight-fitting and nearly always stronger than the wood itself, all that a one-piece bridge would do is create a structure that tends to split and crack along the grain direction. That's not really an ideal scenario for an SO bridge.
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Re: Bridge Designs

Postby SPP SciO » October 17th, 2015, 10:49 am

Great points, thank you. I think I will have the students try the idea by building small hollow cubes, one from 12 sticks and one carved from a block - will post results if/when results come to fruition!
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Re: Bridge Designs

Postby brayden box » October 19th, 2015, 5:56 am

SPP SciO wrote:Great points, thank you. I think I will have the students try the idea by building small hollow cubes, one from 12 sticks and one carved from a block - will post results if/when results come to fruition!

Last year at states, there was a team who had carved their bridge out of a block of wood with a laser. It looked awesome and really strong, but it performed terribly. (It also weighs a lot, because you can't change what kind of wood you use) The sticks and glue method works a lot better.
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Re: Bridge Designs

Postby andrewwski » October 20th, 2015, 12:58 pm

I've seen teams laser cut them from balsa sheets before - they generally don't seem to do well. The grain is the biggest issue - you want to load along the grain, but there's no way to do that when cutting all from one piece. It can also be harder to avoid imperfections in the wood.
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Re: Bridge Designs

Postby Unome » October 20th, 2015, 1:23 pm

andrewwski wrote:I've seen teams laser cut them from balsa sheets before - they generally don't seem to do well. The grain is the biggest issue - you want to load along the grain, but there's no way to do that when cutting all from one piece. It can also be harder to avoid imperfections in the wood.

You're still active!

Back to the topic: the only time I remember hearing of a laser cut piece was at last year's Nationals (I think the picture is on the Best of Nationals page)
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Re: Bridge Designs

Postby JonB » October 20th, 2015, 3:32 pm

Unome wrote:
andrewwski wrote:I've seen teams laser cut them from balsa sheets before - they generally don't seem to do well. The grain is the biggest issue - you want to load along the grain, but there's no way to do that when cutting all from one piece. It can also be harder to avoid imperfections in the wood.

You're still active!

Back to the topic: the only time I remember hearing of a laser cut piece was at last year's Nationals (I think the picture is on the Best of Nationals page)



That would be us. We laser cut tension pieces only. We do laser cut balsa for Wright Stuff, but I do not think we would ever laser cut any pieces of balsa for bridges. The balsa pieces are relatively short and easy to get right when cut by hand. Bass on the other hand is really tough to cut accurately by hand in really long pieces.


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