North Augusta High School students Amy Baxley and Tim James watch as judges George Nelson and Kenneth Taylor test James' design. ANDREW DAVIS TUCKER/STAFF

in most cases, though, the model bridges start to bend and snap soon after Mr. Taylor cranks the vise he made specifically for the competition, which began in 1972.

On Wednesday, 75 students attempted to beat the vise's three pressure points by building a truss bridge with plenty of triangular supports and extra balsa in the right places.

Emily Riley, a ninth-grade honors math student, jumped to avoid a piece of flying wood during the competition when her bridge experienced a break. Her bridge was able to withstand 65 pounds, however, putting her in first place.

"I didn't think it would hold anything," Emily said. For her first attempt at bridge building, Emily's father, an engineer, helped her download a program off the Internet. She used it to test different structural possibilities.

Mr. Nelson, a structural engineering consultant, said Emily's bridge held the weight because she read the instructions.

"She strengthened where she should have," he said.

Each bridge must be 22 inches long, 3 inches high and 2 1/4 inches wide. What does change each year is the location of the pressure points where the bridge will most likely fail because of a lack of joint strength.

Mr. Nelson mounts weights onto a bridge. ANDREW DAVIS TUCKER/STAFF

Seniors Richard Adams's and Charles Johnson's bridge snapped at 3 pounds.

"They did this for extra credit. Can't you tell?" said Karen Williams, the head of the math department.

Ms. Williams grades each bridge on design, workmanship, strength and proper dimensions.

This year, one student purchased a ruler at a discount store and cut all the balsa by it, only to find out the ruler was an eighth of an inch off.

"Luckily, I had an extra bundle of wood," she said.

Reach Carly Phillips at (803) 648-1395 or carly.phillips@augustachronicle.com.