25 Bridge Building Tips

1. Humidity affects the weight of your bridge. Keep your bridge in a closed container with a few grains of rice. or some silica gel packets.

2. Go easy with the glue bottle. As a general rule of thumb, if you can see it then you are using too much.

3. Keep your hands clean! Oils and grease from your skin can ruin your glue joints.

4. Perfect practice makes perfect. The more bridges you build, the better your construction skills will be.

5. Keep your bridge from twisting by using lateral bracing.

6. An L-beam is more efficient than a square, but harder to build.

7. Balsa wood comes in a wide range of densities and stiffness. Weigh each piece that you buy.

8. It is cheaper to buy Balsa in sheets and cut your own wood strips.

9. It’s still true, measure twice and cut once.

10. Keep a log of every bridge you build. Record notes and dimensions; you won’t remember later on.

11. Try to videotape testing your bridge. You may get a clue on what failed first.

12. Always keep safety in mind when using sharp tools. Most mistakes are made when you aren’t paying attention.

13. By cutting a piece in half, you more than double its strength in compression.

14. Good lighting when working will help you perfect those little details.

15. Always test your bridge before taking it to a competition, but leave enough time to build another.

16. Draw out your bridge on graph paper to make sure that it is symmetrical. I prefer the 11″ x 17″ graph paper.

17. Different trusses have different ways of spreading out the load.

18. Wood has about the same strength in tension, no matter how long it is.

19. CA glue is a fairly strong, light, fast-drying glue used by many builders.

20. Balsa wood sands very easily. Be careful not to sand off too much.

21. You can mix wood glue with water to cut down on weight. Doing this also helps the glue to seep into the wood, creating a stronger joint.

22. Remember to close your glue bottle when you are done using it.

23. Basswood will bend easier than Balsa wood. Try steaming or soaking your wood to help it bend.

24. Use Lap joints whenever possible to get the best strength.

25. What you want to look for in glue: drying time, price, weight, and strength.

These bridge building tips will give you a head start when you start designing and building your model bridges. These tips come from my years of experience starting from my time in the Science Olympiad competition and continuing beyond building for fun. Disclaimer: these tips are my own opinion based out of my experience. Other builders might have different views and we might not agree. I encourage you to try things out on your own and decide for yourself what is the best way to build a bridge. Who knows, I could have been wrong about something.

41 thoughts on “25 Bridge Building Tips”

  1. I’m building a balsa wood bridge in class. We are applying the weight on the base of the bridge so what design would be most effective for this type of test?

    Reply
  2. This very much helped my bridge, however its caving in. How do I fix. Its the humidity and im doing this in class, so I cant use a container with a grain of rice. I NEED HELP ASAP because its due NOW!!!!

    Reply
  3. If you glue everything together than cover everything in a ton of glue and let it harden you will have a super good bridge also triangles are your friends.

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    • So true. Triangles are really good for holding weight because they distribute the weight evenly, and you should make the triangle symmetrical but really any triangle will do

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    • the process did work, however don’t soak it too long or you’ll have a bendy bridge… you know what i mean it wont hold anything it’ll just bend and break mine did break and bend but the second time i did it i put it in the oven and it worked way better than the first time it held up 55 pounds and it weighed 22 kg i got an a plus and got two tickets to a hooks game and there i was sitting there and i was proud of myself with failure comes success and you won’t succeed if you fail once or twice!
      Practice makes Perfect (:

      Reply
  4. I once built a bridge for an Odyssey of the Mind competition, and now I have to build one for an Engineering class. I remember my OM coach drying out the bridge in an oven. She set the structure on a cookie sheet and then sprinkled silica gel on the sheet before baking it. I don’t remember the specifics but would like to try this trick for a better efficiency ratio. Do you know anything about this weight-saving method?

    Reply
    • Erik,

      What I have heard is that baking a bridge in an oven has only temporary gain in weight loss. The moisture that is removed by the oven is quickly replaced by the humidity in the air. Also, you have to be careful about the heat level and what glue you are using.

      Reply
  5. Random factoid for those interested,when you put a beam in compression the formula for the weight it can hold is P = c * (E*I)/L^2 where P is you load and L is the length. Making a beam half as long actually increases the weight capacity by 4. Similarly cutting it down to a fourth the size increase the weight 16 fold.

    Reply
  6. how do you build a suspension?
    I’ve been to the summer camp to learn those stuff but they didn’t told me how to build a suspension??

    Reply
  7. Any tips when using squared cross section popsicle sticks to avoid uneven beams or elements (because of different cross section dimensions between one stick and another)? And… should I cut sticks ends in angle to exactly fit between other 2 sticks forming an angle?

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