Thing: Bridge-building 101

>> Assignment: Compare and contrast two popsicle-stick bridges, then crush them to a pulp

by PHILIP PREVILLE

At its best, engineering school is like scientific arts and crafts. Canadian universities host such bizarre events as cement-toboggan races and concrete-canoe regattas. On Friday, March 3, Concordia plays host to its 16th annual bridge-building competition. Teams from 14 universities will build one-metre-long bridges using only popsicle sticks, Lepage's white glue and dental floss. Each entry is judged for its aesthetic value, then clamped into a hydraulic press and crushed.

Believe it or not, many models manage to withstand loads of well over 2,000 pounds. The trick is to distribute the weight of the load throughout the structure. Here's a look at two previous designs by Concordia students and how they fared.

No one at Concordia remembers when model #1 was made, probably because it is eminently forgettable. The curved superstructure beneath the deck could not hold even a mere 150 pounds. Why? Because, when the load presses down in the middle, the superstructure distributes the weight back up along the curve. In other words, it's distributing weight upwards--and not even civil engineers can defy the law of gravity.

Model #2, Concordia's 1989 entry, was very similar--and yet it was much more successful. The curved deck spreads the load to either end of the bridge. But the deck doesn't flatten out because the horizontal beam underneath holds it in place. The way this bridge distributes weight, the load is trying to stretch that horizontal beam--and if you've ever tried to break a popsicle stick by stretching it, you know how sturdy it can be. This bridge held over 400 pounds before finally giving way.

Final factoid: One team once showed up with a popsicle-stick model of a covered bridge. It was beautiful, but couldn't support a feather pillow. "Some students just want to build a beautiful bridge, while others obsess over the strength of their structure," says Wissam Zalzali, president of the Canadian Society for Civil Engineering (Concordia chapter). Some have been known to spend all their nights in the lab, testing different joints and structures for months on end.

The competition is open to the public. Bridges are on display in the atriums of the Hall and McConnell Buildings beginning at 10 a.m.; the crushing begins at 3:30 p.m. :