There was one major complication. Instead of being provided with sand to load our towers as the rules specify, we were given pebbles. You can probably imagine the thoughts running through my mind.

But I was surprised at how much my tower held, 14.6kg, and took home a gold. Now on to states. I am hoping for a sub 7 gram tower.

Most of the bridges similar to this design did not have the additional diagonal bracing from the top to the bottom chords. I think this basic design is a good example of trying to figure out a problem without boxing yourself into thinking of only typical bridge designs. This design takes what you have to do and does it very simply. Most of the time, simple is better.

It is pretty easy to see how this bridge failed: the bottom fell out. This is a fairly easy fix, and might have been due simply to poor wood selection. Had I paid more attention to the quality of wood I was using, this failure might have been avoided.

I used two pieces for the arch. I had a square 1/16″ x 1/16″ piece of Basswood for the bottom of the arch. Then I glued a rectangle piece of Balsa wood on top of that to form a T beam. This method worked pretty well, but Balsa is harder to bend than Basswood.

Although it took me 12 hours (whew..!) I could see the good result! It held 15kg!

I saw some other members’ bridge and recognized that the height and span things were different from our rule which is held in New York.

But there is one little problem. My bridge weighs 111g. I don’t understand why. I used balsa wood and bass wood both and only used 1/4×1/4 size. I think using only 1/4×1/4 is the main problem. I can’t upload the picture somehow, so I uploaded them separately. Please help me reducing the mass. Also, when I was
testing the bridge, there was a cracking sound. Can you tell me what that sound means?

It would be great to get advised from all of you.

These two questions are dealing with making an elevated bridge, very similar to the Science Olympiad challenge.

1: I’m currently building an elevated bridge (for my physics class, not for scioly) and I have finished the two trusses and connected them and now only need to add the towers. Would it be a good or bad idea to make the towers slant outwards or should I just have them go straight up and down?

The only benefit to slanting the towers is that the main trusses can be a little shorter. This will reduce the weight of the bridge. The forces will increase on the towers if they are slanting, and then the towers will have to increase in weight. There is a balance to find. Since you have already built the main trusses, slanting the towers will not really help you. Also, it is significantly easier to build the towers so they are straight up and down.

2: For the bracing on the towers, I want to make X’s but I’m not sure how to do it exactly. Would I put one diagonal piece on one side of the corner and the other piece on the other side or put them on the same side and have one overlap the other?

Good question. I would recommend that you overlap the X’s. The X’s themselves do not need to be large pieces and thus won’t add a lot of weight. Rectangle shaped pieces work best. 1/4″ wide and 1/16″ thick should be more than sufficient. In one tower I built, the X’s were 1/32″ deep and 3/32″ wide. I never had a problem with the X’s breaking, it was always something else that failed.

Here is my Science Olympiad Tower.

Elevated Bridge Resources:

Diary of a Bridge Builder

SciOly Elevated Bridge Thread

I really have nothing on this bridge. I have no idea what team it is from, how much it weighed, or how well it did at the Science Olympiad competition.

I have a picture of it, well, because I had a camera, and the bridge was there. So if you have seen this bridge before, and have some info on it, I would love to hear from you.

I Beam Bridge

This was one of my earlier bridges. I built it after talking with my uncle, who is a mechanical engineer. He suggested that I try using an I-beam. This was a very good idea, but my construction skills at the time were not the best. In theory an I-beam is excellent for bridges, but I could not make it very well.

I don’t know how much this bridge weighed, but it did not hold very much weight.

I had problems making the two I-beams for this bridge. I had to cut my own strips of wood, and I was not very good at doing that yet. The wood I used was very thin, perhaps too thin. I believe I used 1/32″ x 1/4″ strips.

I could not cut the wood strips very straight, and that was the downfall of this bridge. The pieces to the I-beam were not glued together well at all. I was trying out some unique things with this bridge. And if I had better building skills, it would have turned out much better. In later years I was able to make good I and T beams which performed very well.

Boy does this bridge bring back memories. I built this bridge in 2001, in the 7th grade. It was my first attempt at building a bridge on my own after building this bridge with my partner.

I had wanted to make an arch bridge, much like the Booth Bridge, but I didn’t have the building skills to do join the arches in the middle. So I simply made an A frame bridge. I never knew how much it weighed as our Science Olympiad team did not have a scale back then. The bridge held about 30 pounds, just 3 pounds short of the magical 15 kilogram mark (33 pounds). Back then the Science Olympiad bridges had to hold the entire 15kg or they would be ranked in the 2nd tier.

This bridge was built only out of basswood, except for the roadbed. Even back then I understood the power of Basswood . I used Epoxy glue to build this bridge. That is because my bridge building coach used it, and I followed his example. I don’t use epoxy glue for bridges anymore, though I have used it for other things. Read more about choosing the right glue.