Structure strength

This discussion area is for basic structure building concepts. Not intended for advanced concepts.
*Good Example: Balsa can bend with the addition of boiling water.
*Good Example: Triangle is the strongest shape for most applications of bracing.
*Bad Example: Balsa can hold X pounds under these conditions.
*Bad Example: Use this shape for this application.
Basically I want you to think a design through with the basics instead of someone else thinking through your design for you.
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Structure strength

Post by Taishaku » Fri Mar 24, 2006 12:30 am

My Physics teacher wants us to build a bridge with balsa without laminating.

It has to have an 8 inch base and 6 inch top... so there's no support being put on the pedestal it's placed upon.

Which structure is stronger? Trapezoids or domes?

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Post by GmL » Sat Mar 25, 2006 7:25 am

I am not entirely sure - but this edges on OA. Granted your project is not OM or DI related, but giving information as to which shape is stronger could be interpreted as OA for other builders here.

Can anyone confirm if this could be OA for others or not?

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Post by Garrett » Sun Mar 26, 2006 9:04 am

I am not too familiar with the "OA" rule, but to some extent you have to get assistance to be able to do anything.

Taishaku, you can build either a dome (I am assuming this is just an arch bridge) or a trapezoid and make it strong. Other considerations are how easy each is to build. A dome would involve bending wood, which is a time consuming and frustrating project for a beginner. And because of that, you may end up being able to build a better bridge out of a trapezoid.

Or, if you have time, build both a dome and trapezoid bridge and test them beforehand.

But remember this, even if a dome was inherently stronger than a trapezoid (which it may or may not be), the quality of construction is the final factor in how strong the bridge will be. If you build a dome bridge poorly, it will hold less than a trapezoid that is build well.

I don't think, however, that a dome is inherently stronger than a trapezoid in any given situation. It depends on how the bridge is loaded, and other factors.

Another thing to consider. Your teacher doesn't allow lamination. And it only makes sense that the larger the piece of wood is, the harder it is to bend. Therefore, you are limiting yourself as to the size (strength) of a domed bridge.

But don't think I am trying to steer you away from an arch bridge. I personally think arch bridges are more pleasing to the eye. And while in none of the competitions I have been to do the judges count that as a factor, other it is always impressive to the competitors.

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Post by Taishaku » Thu Apr 20, 2006 9:27 am

OA = Outside Assistance?

Well, I'm doing this for Odyssey or any competition, it's a Physics project at my school.

I basically need to design a bridge with a 8in base and 6in top. The project scoring will be similar to Odyssey's. A stand with a gap 6in across and weights ontop. All the weight therefore must be shifted to the outside.

Would building an arch UNDER a trapezoid present even more strengths? Or is this just a complicated exercise in futility?

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Post by Alexandre25 » Fri Mar 21, 2014 8:36 am

id go for the trapezoids myself

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