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Students learn design skills, build bridges in iAP contest

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By Joan D. Abbott

The annual Chi Epsilon bridge design contest, sponsored each Independent Activities Period by the civil engineering honor society, began yesterday. Contestants will design and build a model bridge from furnished materials; the bridge which carries the highest load will win.

After receiving a kit of parts yesterday, contestants attended lectures and demonstrations to learn about the materials from which they must build their structures. Participants will also attend seminars on structural analysis and learn to use the computer-design program "Growl-Tiger."

During the second week, contestants will test their designs in the structural engineering lab. The final test, which will take place in Lobby 10 on Jan. 10, will involve a loading frame -- affectionately called the "nutcracker" -- which can put up to 4000 pounds of load on the bridges. This final loading, at which each bridge will be loaded to failure, allows contestants "to see what other people have built and [to] compare," according to last year's second place winner Roland K. Springer G. "Sometimes the really slick looking ones fail right away and the rough ones turn out to be the strongest. Last year, a simple beam bridge surprised everyone by winning the contest," he said.

Contestants will use weights to load the structure up to 1000 pounds, then walk along beams connected to the load frame to put additional load on the structure until it fails. Springer described his experience with the nutcracker: "My partner and I were walking up the plank trying to load the bridge evenly. I'd slow down and then speed up trying to keep the loads even. It was very tense. You'd hear a crack and wonder `is it going to fail now?' Finally it broke and pieces of the bridge went flying across the floor of Lobby 10."

The scoring of the contest is based on weight, strength, flexibility and some analytic calculations. The bridge must not deflect more than six inches at midspan when loaded with 1000 pounds. In addition, contestants will predict the failure load for their bridges and receive points for accurate estimates.

Since a heavy bridge could be very strong but would lose points for weight, contestants try to balance strength and weight. To test for flexibility, one support is removed from the model before the final loading. This requires the structure to be strong but not too brittle.

Springer regarded the flexibility of the bridge as the key factor but would not reveal his secrets for achieving it. He would say only that "keeping your bridge flexible and maintaining strength is one of the biggest challenges of all."

Contest organizers made changes to the contestant in hopes of improving it. In past years, contestants did not know the exact loading of the bridge until after it had failed. This year, however, there will be a direct read-out in pounds so that the contestants and the audience will know the exact load each bridge withstands.

Organizers considered substituting man-made materials like graphite or kevlar for wood. But, because the strength of these materials would make the bridges so strong that they could not be loaded to failure by the nutcracker, the idea was rejected.

The contest was open to all MIT students. The majority of contestants are undergraduates, but graduate students have also entered the contest, according to contest sponsor Research Associate Thanasis C. Triantafillou.

Since all necessary theory will be taught during the course of the project, Springer encouraged students of all levels to enter. "A little basic knowledge helps but intuition is one of the most important aspects of this contest. It's just using common sense to build a strong bridge."