Lateral Bracing Joints

By on January 4, 2009

I want to put x-shaped supports on my bridge, but I don’t know how best to join them. I’ve heard of something, I think it’s called a half-lap joint, that I think might work best. You cut half of the wood off the part of the strip that will be the actual joint, and then connect the two pieces at those joint parts. There isn’t any part of the wood sticking out, and they are very connected, I think, as far as how the weight/force is distributed, which I figured would be good. But is there a better way to make an x?

Perhaps a more simply way to describe this is cutting a notch out of both pieces of the X at the point of intersection. The reason to do this is to avoid one pieces laying on top of the other, which makes it slightly harder to glue and adds additional pre-load force on that piece.

However, I think cutting notches is more trouble than it is worth. All the bridges I have built (see my Science Olympiad Bridge ), using X’s for lateral bracing, have had one piece laying on top of the other. This does mean you have to use clamps or tape to hold the pieces down while gluing. But I consider this less of an inconvenience than trying to cut two notches out of the lateral bracing. In fact, most of the time my lateral bracing is so thin that I couldn’t cut a notch out of it even if I wanted to.

The notches must be cut exactly to the right size. If they are even a little too large, then you weaken your lateral bracing pieces. This may not be a problem, however, because most people use pieces of wood that much bigger than they need to for lateral bracing. Still, I do not see cutting notches as the way to go.

Another way around this issue is to not use X shaped lateral bracing. Instead, you could use a zig-zag pattern. This will look like a Warren truss on top of your bridge. A stronger pattern is the Warren with vertical supports for lateral bracing.

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1 thought on “Lateral Bracing Joints”

  1. i realy love this website, it has helped me sooo much, being my first year in science oly. for elevated bridge. some of your designs are so ingenius! do work son!!

    By madi -- February 19, 2009

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