By Denise Brehm
Civil & Environmental Engineering

The MIT Steel Bridge Team placed second at the 2012 National Steel Bridge Competition, out-engineering 45 other teams that had been winnowed from 200 in regional contests. The University of California, Berkeley, took first place at the event, which was held Memorial Day weekend at Clemson University.

The annual contest requires student teams to design an approximately 20-foot scale model of a bridge for a hypothetical site that meets specifications outlined in a request for proposals. Teams must fabricate steel pieces to build the bridge and during the competition, be able to assemble it very quickly. The rules are rigid, reflecting the safety needs and landscape characteristics of an actual site. Bridges must be able to withstand a 2,500-pound load without sagging; a deflection of more than one centimeter, for instance, might be considered too large.

This year’s scenario called for a cantilevered bridge (one end of the structure must extend beyond the supports) to span the imaginary Phantom River, providing access to a new recreational lodge. The rules emphasized the importance of a lightweight bridge, and also restricted each builder — the 12-member MIT team had four — to a small area of the site. The restriction on movement made it more difficult to minimize builders’ downtime, a change that worked in MIT’s favor.

“I knew the restrictions on the builders’ ability to move around the bridge was good news for us, because the MIT team has always been able to come up with efficient construction sequences very quickly. This gives us an edge over some of our competitors,” says Pierre Ghisbain, a doctoral student in the Department of Civil and Environmental Engineering (CEE) who served as mentor to the undergraduate team. Ghisbain’s research is in earthquake engineering and the optimization of structures.

Designing for speedy construction

Instead of using pins to connect bridge pieces and bolts that need tightening, this year the team chose to use pieces that connect via slots and lock-in when rotated, a method that cut construction time significantly. Although a dropped bolt cost the team a time penalty, the construction time of just under seven minutes was still fast enough to earn the team fourth place in that category. The first-place Berkeley team took the top spot in construction speed with a time just shy of five minutes.

“A huge part of our success was due to a very well-optimized bridge design by Pierre,” says team co-captain Jennifer de Bruijn ’12. “Without a design that is both light and stiff and keeps the number of pieces to a minimum, we wouldn’t stand a chance.”

Ghisbain said de Bruijn’s experience as a builder on the 2011 team was critical in helping the 2012 team understand how design decisions would impact construction time. This allowed the team to complete its bridge design early and have more time for practicing construction.

“Without the hours we spent building the bridge over and over again, we wouldn’t have managed to lose three minutes in our construction time between regionals and nationals,” says de Bruijn, who is now a graduate student in environmental fluid mechanics at Stanford University.

Teamwork is key

This was the sixth year that MIT has participated in the competition. In 2010 the team broke into the top 10, placing sixth, then moved up to fifth place in 2011. Each year, the team has placed ahead of other private schools, which tend to have trouble competing with the much larger teams from big state schools. Smaller teams require a greater time commitment from team members, but the MIT students say the project is well worth it.

“One of the main things I got out of participating on the team is a solid appreciation for hands-on engineering,” says de Bruijn. “Steel bridge forces us to consider the overall design as well as the details of how it will go together. It isn’t possible to design a good bridge without designing the connections at the same time. We learn to appreciate the difficulties associated with making the ideal connection, such as the limitations imposed by the accuracy with which a machine can cut and the distortions that occur when metal undergoes the intense heat of welding.”

Team members were de Bruijn and co-captain Leonidia Garbis ’12, Rebecca Hawton ’12, Scott Landers ’12, Alexander McCarthy ’14, Sante Nyambo ’15, Reece Otsuka ’12, Stephen Pendrigh ’12, Nicholas Soane ’12, Justin Sousa ’12, Maria Tou ’14, Alexis Ludena ‘14 and Sharone Small ’14.

Professor Jerome Connor and Ghisbain advised the team; Jimmy Duffy and Jimmy O’Donnell of Boston Bridge Services provided pro bono welding and fabrication; and CEE technical instructor Stephen Rudolph spent many hours acting as mentor, instructor and chief fan of the team.

“We are incredibly grateful, not only for the hours Steve puts in and his attention to detail when critiquing our designs, but also for his cheerfulness and great sense of humor,” de Bruijn says of Rudolph. “Steel bridge would be much less successful and fun without him.”

This was the 20th year of the competition, which is sponsored by the American Society of Civil Engineers and the American Institute of Steel Construction.