100 Stick Popsicle Bridge: 21″ Howe Truss

The 100 stick popsicle bridge challenge is on. This Howe Truss bridge uses 99 popsicle sticks, spans 21 inches, and holds 200+ pounds. It’s efficiency score is 678. This is an updated version of my old “Popsicle Bridge #3” which was the same length, but slightly different in construction.

This bridge was built from completely un-modified popsicle sticks, Level 1 sorted. I used only Elmer’s White glue to join the sticks together. To test the bridge’s strength I raised the ends up off the ground with wooden blocks, and placed free weights from a weight set on top of the bridge. I did my best to keep the weights centered over the bridge and to place them down gently, and I do not think the bridge broke because of the method of testing.

These three photos show the progression of the bridge breaking. Watch the left side as it starts to fail.

Slow Motion of the Bridge Breaking

My conclusion based on these photos is that the lateral bracing on the left side popped off from the side of the bridge closest to you in the photo. This caused those angled popsicle sticks to twist, and the bottom chord starts to twist a little as well. I think it was a glue joint that came loose and started the chain reaction. The angled sticks on the ends may not have been perfectly even and square with each other, which would have caused a weaker joint.

The other possibility is a weak popsicle stick, which started to fail and then brought the rest of the bridge down with it. I only used a level 1 sort for these popsicle sticks, so this is possible.

Here we have a shot of the bridge holding some weights. Also you will see the analysis of this Howe Truss Bridge as shown by the free Bridge Designer program. This picture shows how the forces were spread out on the bridge at the time it failed. Notice how the forces are concentrated much higher in the middle of the top and bottom chords, as well as on the end angled members. This supports my thought that the left side angled members would have failed first. They were under a very significant load.

So now you have seen the video, and the photo evidence. How do you think the bridge broke first? What would you do to make this bridge better? Keep in mind that I was building under a 100 stick limit constraint.

Build this Howe Truss Bridge

If you are interested, you can purchase the blueprints to build this bridge in my store, and you can also buy a complete kit to build this bridge.

44 thoughts on “100 Stick Popsicle Bridge: 21″ Howe Truss”

  1. Garrett,

    I don’t want to burst your bubble but the way in which you tested this is completely incorrect. The only thing you tested was the compression capacity of the very end diagonal members. When I watched your video it’s very obvious that the way in which the bridge failed was that you buckled the end diagonal member. The member buckled out about its weak axis which then caused the first interior vertical to fail and then the whole thing was a progressive collapse. You didn’t test any of the interior chord or diagonals for their axial capacity because you loaded the bridge incorrectly. You used large circular steel weights that spanned the entire length of the top chord. Those steel weights are a hell of a lot stiffer than your wood bridge which means 95% of your bridge was experiencing zero load. All the load was being transferred down your lasts diagonal members to the supports. You need to point load your bridge at the center.

    I found this while searching other Popsicle stick bridge builds and wondered how many poor souls followed your design only to be sorely disappointed.

    Reply
    • Stephen, thanks for your insight. I’m mulling over what you said.

      On a side note, this bridge’s design and the method of testing were based one of the more common practices for loading model bridges. For its purpose, I wouldn’t say it was incorrect but rather it might not be the best way to test a model bridge to get a true picture of its efficiency. Still, I’ll definitely keep this in mind when loading new bridges. Most everyone who has built this bridge has been pleased with its performance because the instructions make it easy to reproduce consistent results.

      Reply
  2. 2 things, I am in elementary school and I am building a popsicle stick bridge. Anyways, 1. what kind of glue did you use to hold it together, 2how long is the bridge?

    Reply

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