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I was testing my bridge today and saw no signs of bending, but then an inner diagonal member buckled and broke (the piece going from the top compression member on one side up the bottom tension member on the other side). It was a singular diagonal piece, not an X. What can I do to prevent this from happening? should I make an X?

Without a picture it is difficult to offer a firm suggestion.
If it buckled, that member was in significant compression. The trick is to find some way to have another member in tension that will stop the buckle.
In some applications, an X brace will help.
A bigger or stiffer member will help some.

jasontang wrote:I was testing my bridge today and saw no signs of bending, but then an inner diagonal member buckled and broke (the piece going from the top compression member on one side up the bottom tension member on the other side). It was a singular diagonal piece, not an X. What can I do to prevent this from happening? should I make an X?

Yes, I agree with retired1. It would be helpful to have a picture or diagram and it would be possibly the only way I can accurately help you. Feel free to send a diagram as a message if you don't feel comfortable posting it publicly.

At regionals this Saturday, we saw a couple of bridges that held their weight from the top, what advantages would that have? Our team won 1st in Varsity and 1st and 2nd in JV

Our bridge always seems to tear away at the bottom right before we make it to full load. Basically our sides and top areas are intact, but the wood at the bottom just pops off. We tried adding gussets, but the gussets tear in half as well. We tried a different glue but that snapped as well. We use normally use Loctite. Is this a design problem or is it a wood problem? Any suggestions?

IvySpear wrote:Our bridge always seems to tear away at the bottom right before we make it to full load. Basically our sides and top areas are intact, but the wood at the bottom just pops off. We tried adding gussets, but the gussets tear in half as well. We tried a different glue but that snapped as well. We use normally use Loctite. Is this a design problem or is it a wood problem? Any suggestions?

Since this seems to happen with every bridge, I would say it is a design problem. But I can't be sure since I have almost no idea what your bridge looks like.

IvySpear wrote:At regionals this Saturday, we saw a couple of bridges that held their weight from the top, what advantages would that have? Our team won 1st in Varsity and 1st and 2nd in JV

It depends on the design. Placing the loading block on the bottom wouldn't work for me since I only have tensile members on the bottom, which can't hold much.

In a bridge loaded at the top . . . the top beams would be in compression while the bottom member would be in tension. If the load was moved to the bottom, the two swap places correct? If loaded at the bottom, the bottom would be in compression and the top in tension. Does anyone know of a good computer simulation for determining which pieces are undergoing which force?

SOCoach wrote:In a bridge loaded at the top . . . the top beams would be in compression while the bottom member would be in tension. If the load was moved to the bottom, the two swap places correct? If loaded at the bottom, the bottom would be in compression and the top in tension. Does anyone know of a good computer simulation for determining which pieces are undergoing which force?

Incorrect. The bottom would still be in tension and the top is in compression. Though that is quite generalized, as it really does depend on your design. But in general, the top is always compression and the bottom is always tension. I suggest JHU bridge builder.

So regardless of where the load is placed (generally) . . the top beam is always in compression and the bottom is in tension.

but if the load is placed on the bottom are the vertical supports from the top to the bottom of the bridge in tension? It would seem to make a lighter bridge you'd want as many pieces in tension as possible because those pieces can be lighter.