Balsa Bridge

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.

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?

    Reply
    • 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.

      Reply
  2. 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?

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  3. 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

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    • 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?

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      • 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.

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  4. 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.

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  5. 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

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  6. 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?

    Reply

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