Monday, November 11, 2013

Building Paper Bridge Models (beam, arch, and truss bridges)

As we moved past the Renaissance and Baroque eras, it was on to the Industrial Revolution and the rise of Iron as a building material. And this began Bridge Week. I wanted to spend a whole week on bridges because we had this great book full of activity ideas, and also because, as I've mentioned, we have a bridge lover in the family! Bridges were also a good way to move through history, because some of the first cast-iron structures were bridges, and then with the development of wrought-iron and even stronger steel, bridges again demonstrated the capabilities of these new materials.

Do you know the difference between iron and steel? We learned about it here.

With a discussion of bridges, we got to review some architectural principles: the triangle (or Truss Bridge), the post-and-beam structure (or the Beam Bridge), and the arch (or Arch Bridge). We made the simplest of paper models to demonstrate the strengths of each style of bridge.
You can see how many more paper clips the arch bridge, compared to the beam bridge, can hold before it starts to buckle.
But look at the truss bridge! The truss is simply a folded paper that makes triangle shapes between two flat sheets (kind of like corrugated cardboard). It held our entire jar of paper clips without buckling!

We also compared two variations on the arch bridge: one with vertical supports, as above, and one without.
We loaded both bridges with equal weight to compare their response to a load. As expected, the reinforced arch held up much better.

Here is a really fun video showing the loads that can be borne by different types of bridges (including Lego Men in danger!):
Part I here

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