Breaking Point

By building and testing bridges to the point of collapse, engineering students get a real-world lesson in the art and science of structures
In the video above, Tufts engineering students submit their bridges to the weight-bearing test. Video: Steffan Hacker
November 8, 2012

Share

They’ve got limited resources: a fixed amount of basswood, Elmer’s glue and an X-Acto knife. The goal: span an 18-inch gap with a bridge that holds as much weight as possible. That’s the plan at least, as teams of engineering students in Masoud Sanayei’s structural analysis course prepare for an annual competition, where they will learn real-life lessons.

“These are junior structural engineers with limited knowledge of applied mechanics and structural engineering in bridge design,” says Sanayei, a professor of civil and environmental engineering.

The teams put their designs to the test in a public contest of strength and skill, with bridges rated on aesthetics, load carried and efficiency (the ratio of bridge load to weight).

This year’s entries included colorful bridges that twisted, bent and snapped under loads ranging from less than 20 pounds to nearly 200 pounds. In a previous competition, one bridge withstood 376 pounds, still the record.

The “spaghetti” bridge from an earlier competition, a spectacular failure. Photo: Courtesy of Masoud Sanayei“They see there are so many ways for a structure to fail,” observes Sanayei. And it is failure that describes Sanayei’s most prized possession—a photograph of what he calls the “spaghetti” bridge—a warped and buckled span that was terribly designed and thus collapsed spectacularly during one competition.

“Understanding structural failures is crucial to the learning process,” says Sanayei, who requires the students to write a detailed analysis of where and why their bridges failed—and how they would go about preventing such failures.

“This is a real learning experience for structural engineers who, in the future, are going to design our highway bridges for safety, efficiency and durability,” says Sanayei.

Julia Keller can be reached at j.keller@tufts.edu. Steffan Hacker can be reached at steffan.hacker@tufts.edu.