Footbridges carry students from theory to practice
By Denise Brehm
Civil & Environmental Engineering
Students in the senior engineering design class (1.013 Civil Engineering Design) once again designed and built portable footbridges that could be used in a savannah climate where seasonal streams crop up, then dry up once the rainy season ends. The CEE seniors assembled and tested the bridges at lunchtime May 16 on the Student Center Plaza, where a small crowd gathered to watch.
Bridge requirements were straightforward, in keeping with the intended use. The assignment stated that bridges should be 10 feet long, 2 feet wide, and provide 2 feet clearance at the highest point. They must be light enough to be carried to and from the stream, and, unless carried in one piece, must be easily assembled on site using only hand tools. Materials are limited to those commonly available in the developing world. Bridges must be able to handle a load of 2,000 pounds total or 100 pounds per square foot, with a prescribed maximum amount of deflection.
The four teams came up with four entirely different bridges, which isn’t unusual, according to lead teacher Professor Herbert Einstein. “Since we started doing this project in 2000, there are maybe two or three bridges that are similar. This year, three were completely different from what has been done before,” said Einstein.
One team designed a one-piece arched bridge constructed of a 1.5-inch thick concrete slab covered with CFRP (carbon fiber reinforced plastic) sheets. It weighed 200 pounds and handled a 2,000-pound load of concrete blocks in addition to its four creators, who stood atop their footbridge to add extra weight.
“Even with that 3,000-pound load, our bridge had no measurable deflection,” said team member Joseph O’Connor, who gave a very simple explanation for the team’s choice of the arch design. “We wanted to do something with a very simple look. And the arch is very elegant,” he said.
Structural engineers Lisa O’Donnell and Bashar Altabba worked with Einstein and the students on the assignment, and technical instructor Steve Rudolph helped students in the lab.