Building balsa bridges, then breaking them

Posted: Wednesday, October 29, 2003

A Building Balsa Bridges presentation and activities will take place in the Juneau-Douglas City Museum on Saturday, Nov. 8, from 1 to 3 p.m.

The Museum will have a balsa bridge presentation on how truss bridges and beam bridges are constructed and then several balsa bridges will be tested to failure.

Testing will be a smashingly good time! Kids can try their hands at making truss bridges out of gumdrops and toothpicks. A balsa bridge display including bridge photos from past contests will be set up.

For the past nine years, the American Society of Civil Engineers has sponsored an annual Balsa Bridge building contest. The group is continuing this tradition by hosting the 10th Annual Balsa Bridge Contest on March 6, 2004.

This contest is intended to promote interest in engineering, math, and science. It provides an opportunity for students of all ages to learn basic engineering concepts and building techniques.

The annual contest is split into three age divisions: Junior (grades 8 and under), Senior (grades 9 through 12), Adult, and two bridge categories (truss and beam).

Bridges are designed and constructed by individuals or teams of two. The winning bridges are the ones that have the highest efficiency, which is calculated by dividing the load the bridge carried at failure by the weight of the bridge. For instance, last year's Junior Truss winners, Hans Petaja and Thomas Sorenson, won with an efficiency rating of 687. In other words, their bridge carried 687 times the bridge's weight.

Other winners in Junior Truss were Austin Dukowitz and Nathan Graves. The winners in Junior Beam were Gabrielle Worden, Grayson Carlile and Austin Dukowitz. The Senior Truss winners were Matt Voelkers, Carl Broderson and Nichole O'Brien. The winners in Senior Beam were Carl Broderson, Matt Voelkers and Taylor Smith. The Adult winner was Gary Scarbrough. His beam bridge had an efficiency rating of 3745!

PE Civil Engineer Travis Arndt and Gary Scarbrough, a bridge inspection manager, will run the event at the City Museum. Both work in the Bridge Design section of the State Department of Transportation. Gary has participated in the last five contests and says, "Want to have a smashing good time? Come and watch as balsa bridges are crushed to pieces. Learn why the bridges fail so you can get ready for the 10th Annual Balsa Bridge Contest."

Rules and specifications for the 10th Annual Contest will be available at the City Museum during the Building Balsa Bridges event.

Travis and Gary will also lead a workshop on building balsa bridges on Feb. 28 at the City Museum. Participants will learn about the strengths and weaknesses of different types of balsa bridges, properties of balsa wood and simple engineering principles. And they will have the opportunity to make a truss or beam bridge. Class size is limited, pre-registration and a materials fee are required.

The Juneau-Douglas City Museum is at 4th and Main streets and is a program of Juneau Parks and Recreation Department. For more information, call 586-3572.

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