Balsa Bridge

By on May 25, 2006 -- Modified on August 17, 2017

This balsa bridge was built by some students of mine for a Science Olympiad competition. It spanned 14 inches, weighed 8.1 grams, and held 29 pounds. That puts its efficiency at 1630.

This photo makes the bridge look a little lopsided. That wasn’t the case, however.

Here is a photo of where the bridge broke. Click the picture to get a really good close-up.

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27 thoughts on “Balsa Bridge”

  1. I have to build a bridge that will be tested with one side elevated 5cm higher than the other. It’s not elevated as part of the bridge but there’s a block that has to elevate it. Also, the lower end of the bridge must be 2.0cm or less in height perpendicular to the test support at the end of the test support. Do you have any advice on designs for this?

    By Sam -- October 18, 2015
    • Hi Sam,

      This sounds like Science Olympiad. Am I right? If so, Science Olympiad bridges are all about simplicity. Try to envision how to make your top chords (in compression) the shortest they can be.

      By Garrett Boon -- October 20, 2015
      • Yeah, it is Science Olympiad. Thanks for the advice.

        By Sam -- October 20, 2015
        • Also, if you haven’t already, check out .

          By Garrett Boon -- October 23, 2015
  2. Can you tell me the differance between the span and the length of a bridge?

    By Chris -- April 11, 2012
    • The length refers to the measurement from one end of the bridge to the other. The span refers to how much of the length is suspended over air. For instance, my model bridge might be 18 inches long, but 1 inch on each side rests on blocks. Thus, the span is only 16 inches.

      By Garrett Boon -- April 11, 2012
  3. Any tips for a first time builder Garret?

    By John Rubyslinger -- September 12, 2011
  4. my bridges had a set of x’s on all side it held 60 piunds im in 8th g

    By levi -- February 4, 2010
  5. hey garret do you know what science olympiad is?

    By superstar -- March 20, 2009
    • Yep, I spent 7 years competing in SO, and these past few years keeping tabs on what’s been going down in the SO world.

      By Garrett Boon -- March 20, 2009
  6. i am a 7th grader and i have to build a bridge out of balsa wood and i have 20 ft of sticks to work with. how many feet was used for the 2nd bridge?

    By Wildcat -- February 27, 2009
  7. Garret can u tell me how tall and wide this bridge was

    By Prakhar -- January 18, 2009
    • This bridge was 2 inches wide and 3 inches tall

      By Garrett Boon -- January 19, 2009
      • how long was it and how long was the top part?

        By aperson -- April 10, 2009
        • The bridge was just over 14 inches long, and the top flat part was 2 inches long.

          By Garrett Boon -- April 10, 2009
  8. Im an 8th grader and we are doing this project what do you think would be the lightest yet strongest bottom. Need to know soon!!!!!! Thanks

    By x -- December 11, 2008
  9. I’m looking for blueprints for a balsa bridge for my class prj where’d u find yours

    By Donna -- December 8, 2008
  10. sorry i haven’t been posting much lately been very busy at school with speech and debate.

    By First Timer -- November 26, 2008
    • No worries, I appreciate any time you spend here posting and answering questions.

      By Garrett Boon -- November 27, 2008
  11. The load was placed on top in the center of the bridge.

    By Garrett Boon -- November 26, 2008
    • I am competing in a truss bridge building contest, and I’m not quite sure I understand where they put the weight. If the top of the bridge is covered, do they just put the weight there, or do they put it inside the bridge?

      By Ellie -- January 1, 2011
      • Ellie, I’m afraid I cannot answer your question. I have no idea where your bridge will be loaded. I’d ask the host of your contest, or refer to any rules/guidelines you were given.

        By Garrett Boon -- January 1, 2011
  12. I’m a science teacher and I’m considering having my 8th-graders doing a project like this. Where was the load placed on this bridge? I’m not sure I understand from the pictures.

    By amy -- November 25, 2008
    • i’m in 6th grade and i’m doing this project as well….

      By faith -- February 5, 2013
  13. hey i suggest you strengthen it with some wood wood is fairly strong and light also attatch the wood with a glue of some description

    By david -- November 22, 2008
  14. Say I wanted to build a bridge similar to this, except it will be elevated by two 10 cm columns.
    How would you suggest I strengthen the base of the bridge without adding too much weight?

    By Jane -- November 9, 2008

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