I built this bridge for the 2005 Fernbank Science Center bridge design event. The bridge spanned 16 inches, weighed 37 grams, and held 346 pounds. That puts its efficiency over 4200! One commenter said, “So if this bridge weighed one pound, it could have held up my car.”

Fernbank Project: Strongest Bridge Design

I built this bridge for the 2005 Fernbank Science Center bridge design event. This is the strongest bridge I have ever built. The bridge spanned 16 inches, weighed 37 grams, and held 346 pounds. That puts its efficiency over 4200! I had never even come close to getting this amount of strength out of a bridge design before. I was really surprised. One person said, “So if this bridge weighed one pound, it could have held up my car.”

The first time the bridge was tested it did not break. The testing machine was set to only apply 250 pounds. This bridge was too strong for that! Here is the bridge after the second testing:

The secret of a strong bridge design

As you can see, the bridge stayed mostly intact. I talked to a couple engineers at the event and asked them what they thought made my bridge break. One suggested that the bridge failed in torsion, as I did not have any diagonal braces in the bridge. That is definitely a design flaw I will fix if I do this again. I would love to try and break an efficiency of 5000. That would be a strong bridge indeed!

For more information on this competition, see Atlanta Toothpick Bridge Competition. I encourage anyone in the Atlanta area to try and go to this event. It is free and open to all, both young and old. Try your hand at making the strongest bridge. And when you do, send me photos of your bridge 🙂

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55 Responses to “Fernbank Project: Strongest Bridge Design”

  1. Mike - March 15, 2011 at 11:00 am

    what truss design did u use?

    • Garrett Boon - March 16, 2011 at 4:15 pm

      This bridge used a hybrid truss design. Mostly it was a Subdivided Warren, but went to the Howe Truss on the ends.

  2. Saga - March 15, 2011 at 10:59 pm

    I was wondering, how was the bridge loaded?

    • Garrett Boon - March 16, 2011 at 4:14 pm

      This bridge was loaded from the top with a metal plate that was attached to a hydraulic loading machine.

  3. Steve Amdhome - March 22, 2011 at 2:42 am

    what do you mean by diagonal braces? and how long did it take u?
    i tried to copy your design except with popsicle sticks didnt turn out very well. was kinda crooked and twisted.
    hope i can still beat my class in most durable bridge

    • Garrett Boon - March 22, 2011 at 3:30 am

      Good question. Diagonal bracing here refers to any pieces that would have connected the sides of the bridge on a diagonal. So if I had a piece that was glued on the bottom of the left side and sloped up to the top of the right side of the bridge.

  4. Balsa, Balsa Wood...ha - April 12, 2011 at 7:26 pm

    What kind of truus did you use? A howe, pratt, or warren?

    • Garrett Boon - April 12, 2011 at 10:01 pm

      This bridge used a hybrid truss design. Mostly it was a Subdivided Warren, but went to the Howe Truss on the ends.

  5. Tessa - November 7, 2011 at 5:26 pm

    What kind of popsicle sticks did you use, just regular, or a certain kind. Also, what kind of glue?

    • Garrett Boon - November 7, 2011 at 5:32 pm

      Tessa, I did not use popsicle sticks on this bridge. I used Basswood. I used two types of glue, Weldbond mostly and a little Probond.

  6. Tessa - November 7, 2011 at 7:01 pm

    If this design was used with popsicle sticks would it work?

    • Garrett Boon - November 7, 2011 at 10:22 pm

      Probably, although you might have make some minor modifications.

  7. Sam Witwer - December 2, 2014 at 9:48 pm

    Hey Garrett, I’m Sam, and I was wondering what a good ratio of height to length to width ratio would be for a truss bridge, in general. If you need me to be more specific, then, as an example, let’s assume that we have a Pratt bridge that’s 25 inches long. Do you have any insight on how high or wide it should be then? I’m no expert, so just a general idea would really help me out; if you have enough time.

    • Garrett Boon - December 3, 2014 at 12:14 am

      Sam, I’ve had good success starting with a 1:6 height to length ratio. In general a wider bridge will be more stable but also adds weight. If you are testing the bridge with a load that won’t move around lateral, then a more narrow bridge is fine. But if you are planning on standing on the bridge, you probably want to make it wider. The popsicle stick bridges I make that are 25 inches long are about 3.5 inches wide. This is mostly because of the limitations from using popsicle sticks, but it does seem to work out well.

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