Engineering Structures in Stu-Fac Model Forces at Work
If you stand in one of the most trafficked areas of the dining hall and look up, you’ll see four slender structures extending from a railing overhead. Their fine lines and neutral tones blend in, and in an area of the Stu-Fac that’s often decorated, they can be easy to miss. But look a bit longer, and you’ll notice something about them: they’re suspended from only one side. Extending out 5 meters—long and thin, like skyscrapers on their sides—they’re supported by nothing other than their wooden bases and their own structural integrity. These aren’t sculptures; they’re cantilevers, final group projects from Brad Moriarty’s fall 2024 Topics in Engineering: Structures 1 class.
In this introductory course on structural engineering, students learn what keeps buildings from falling down by exploring the forces of tension, compression, stress, strain, moment, and shear and the basics of structural vibration. They put their knowledge to the test in the last half of the semester, constructing cantilevers. This requires clever application of all these concepts to prevent collapse, and students built some smaller structures to test ideas prior to spending the final six weeks on their projects.
All four team-built structures were sound enough to hang during the exam week just before winter break, and all four started out straight. After more than a month, one hung by itself has curved wildly, and two others have begun to lean on the outermost fourth, which remains mostly straight but has buckled near the base. (Catch wires are strung beneath them all for safety.)
“From an educational perspective, having them fail is better,” Moriarty said as he discussed the project recently. Standing beneath the structures in the Stu-Fac, he took satisfaction in how the students’ work demonstrated the forces visibly at work. He pointed to a prominent bulge near one base, explaining that the longer the length, the greater the strain—it increases not linearly but exponentially, and the greatest forces act closest to the support.
The structures are constructed from only 7-centimeter wooden coffee stirrers and hot glue. To build as light as possible with very little extra mass, each student team created a triangular prism. A rail of single sticks along the top holds the tension, the force trying to pull the structure apart, and two rails along the bottom hold the compression, the force trying to push it together.
“It’s physically impossible to break a coffee stirrer by pulling on it,” Moriarty explained. But the little sticks are vulnerable to compression: they collapse when you push on them. As with real structures, the joints where the pieces meet are where each model succeeds or fails.
Moriarty first developed this course while teaching at Milton Academy, out of a lifelong interest in the way things work and how to make them better. He joined the Concord Academy faculty in September 2022 to teach engineering and physics, and CA students have since taken up this hands-on work with enthusiasm.
Students were graded not on whether or not their team’s structure stayed up but rather on how well they could explain why it behaved as it did. “The idea is to be graded, effectively, by the universe, rather than by me,” Moriarty said. “It’s a very satisfying project.”
