Last spring, undergraduate junior Aimee O’Brien of the Civil and Environmental Engineering Department was the co-captain of the UMass Amherst Steel Bridge Team that managed a strong fourth-place finish out of 12 teams at the regional Student Steel Bridge Competition, run by the American Institute of Steel Construction. With O’Brien doing much of the day-to-day management and organization of the team, while also putting in many hours of hands-on cutting, welding, and grinding, the double-girder bridge took first place in the key stiffness category, boasting an aggregate deflection of only five-eighths of an inch. The approximately 20-foot scale model also weighed in at a relatively feathery 248.8 pounds.
“I learned quite a lot about the management of the project,” says O’Brien, who is also the president of the American Society of Civil Engineers student chapter at UMass Amherst. “But the most important thing I learned was going from the design process to the actual fabrication process and making it work, which was huge. As an engineer sitting there and designing something theoretically on paper or in a computer program, you really have to know if something can actually be done physically in the real world.”
Now, as the captain in charge of running the 2010 Steel Bridge Team, she’s all too aware of practical realities as they affect the design. For instance, will the design allow you to fit a wrench into the real structure and tighten a bolt or to get a torch into a tight spot for welding a joint?
“I’m really aware of those things this year,” O’Brien says.
That kind of hands-on learning, not by coincidence, is one of the main purposes of the Steel Bridge Competition. Since the competition was started in 1987, its mission is “to supplement the education of civil engineering students with a comprehensive, student-driven project experience from conception and design through fabrication, erection, and testing, culminating in a steel structure that meets client specifications and optimizes performance and economy. The competition increases awareness of real-world engineering issues such as spatial constraints, material properties, strength, serviceability, fabrication and erection processes, safety, esthetics, and cost.”
The judges for each annual competition issue a common set of specifications (different each year) to all the teams in the country. The specs give an envelope that includes length and height limits. Each bridge must also handle a load of 2,500 pounds. After designing and fabricating a bridge in the months before the competition, each team must assemble the structure for time during the actual event. Then each bridge is tested for lightness, stiffness, and other factors, and judged for esthetics and total “cost,” which depends on a combination of all these factors.
“The most challenging part of last year’s process was, first, arriving at a design that all 14 team members could agree on, and then making sure that design worked in the real world,” recalls O’Brien.
The team started with three designs. One of them had three lateral girders that underpinned the whole decking structure, but that proved too heavy, so the team settled on two girders oriented strategically for extra support.
“Pretty much the design worked,” says O’Brien, “but we had to tweak a few things that we realized weren’t right. For example, it was difficult to design for cross-members to help with lateral bracing, just because we didn’t know precisely how much the constructed bridge would actually deflect until we actually tested it down in the Structures Lab.”
O’Brien explains that computer designs can’t take into account the “human factor,” such as how strong all the welds are actually going to be, or whether the structural members and the position of the drill holes are all measured precisely.
“Two years ago, for instance, our bridge collapsed under the load,” says O’Brien, noting that most bridges in the competition also collapsed that year. “The reason the bridge failed in the competition is because we had drilled an extra hole in a location that was very critical. You could see it where the bridge broke. That’s a great real-world lesson to learn.”
And O’Brien has learned her lessons well. With all that valuable steel-bridge experience behind her, O’Brien is putting all those lessons to work this spring as team captain. After all, this is not just some classroom exercise, but a real-world bridge to her future. (February 2010)