MIT Steel Bridge Team takes second place at national competition

August 31, 2012

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

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