Tuesday, November 12, 2013

Bridge Resources, and Building a Truss Bridge

The triangle is such a simple shape, but it's so good at handling heavy loads! Like pyramids, which depend on triangles for their strength, trusses combine triangles to make very strong structures. We made a truss bridge out of popsicle sticks to test this engineering principle!

Now, I do realize that this bridge is not as impressive as many built for bridge-building contests, etc. When I was young, there was a bridge building contest at my high school and people were able to do AMAZING things with their little wooden structures. I think they made tiny bridges that people could stand on without them breaking. So, I'm sure we could find many ways to build even better bridges! But for us, making a bridge that could hold up a whole cup of rocks was was a pretty cool feat.

We used hot glue (I am impatient and hate waiting for white glue to dry!) to create these interlocking triangles. The deck of our bridge goes through the middle, making this a Through Truss Bridge, but some bridges also have their decks on top of the trusses.
We tied a cup to the roadway and loaded it with the heaviest rocks we could find!

Balancing another rock on top

I love these surprised faces. Wow, we did it!

We had a very interesting discussion about bridge failure, sparked by this activity here and this article here. There's lots more coverage of the Minnesota Bridge collapse here. We watched videos of the collapse and learned about how engineers went about finding what caused the problem (as well as reasons why the faulty gusset plate may have been ignored in the first place!).

Here's a slideshow about the principles of Tension, Compression, Torsion, and Shear. All of these forces are important in understanding how structures work.

Here's an activity where you can test the strength of different materials in tension, compression, and torsion.

This is a good site for bridge basics and some animations of how basic forces work on objects.

We also watched Building Big:Bridges (available from Netflix) in the evening during our bridge week.

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