Talk about a passion project: University of Washington graduate research assistant Kristina Tsvetanova has logged more than 100 hours a week at the UW’s Structural Research Lab working on one project – one for which she will receive no academic credit (her thesis was about a totally different project).

“She’s put a phenomenal amount of work into this, and I have never told her, ‘You have to be here at this time, doing this,” said her adviser, civil engineering professor John Stanton.

It’s likely because she’ll get something more valuable out of the experience.

“She’s completely engaged, and it’s because she’s excited about being a part of a real-world project that is going to be built,” Stanton said.

Several of the bright minds working to take – a world first – aren’t earning a dime for their trouble. Three UW graduate students and nine undergrads are part of a global team assembled to tackle this . The team also includes an English design engineer and more than 30 U.S. subcontractors – including Portland-based David Evans & Associates and the Portland offices of KPFF Consulting Engineers and WSP. Another of the graduate assistants, Travis Thonstad, even helped author a scholarly article on design development of the project. (Thonstad now works professionally on the East Coast.)

“It was a global problem, so it required a global solution,” said John Sleavin, deputy director of Sound Transit‘s $3.7 billion , which includes at Lake Washington. The 5,700-foot-long span now carries westbound and express lane traffic, and is the widest and fifth-longest floating bridge in the world.

Among the consulting engineers were experts in marine vessels, who were able to consider matters like trim, ballast and how high the bridge sits on the lake. Sleavin said there was in adding a railway to a structure that floats.

“A floating bridge, in the simplest terms, is a marine vessel that cannot go into port,” he said. “It’s basically a ship we’re putting this on.”

There are six degrees of motion that affect a span like the Homer M. Hadley Memorial Bridge, and that engineers in this case had to account for. The hardest piece to get right is the approaches.

To allow the light-rail cars to ride smoothly onto and off of the bridge, U.K. engineer Andy Foan developed a new, highly-responsive track system dubbed the Curved Element Supported Rail (CESuRa).

UW students led by Stanton have worked closely for five years with Sound Transit officials and consultant Parsons Brinckerhoff, primarily involved with lab-testing various prototype materials, like the CESuRa system. Thonstad led testing of the system, starting in 2012, using a custom steel rig that mimics the movements of a train. After that, Thonstad assisted with full-scale testing at the Transportation Technology Center in Pueblo, Colo.

The rail cars were tested at 55 mph. Playing the role of human passengers: barrels full of water.

“They actually do a pretty good job representing how a human body reacts in those circumstances,” Sleavin said. “And we obviously can’t use real passengers.”

It’s fitting that students were so involved in an innovation to a bridge that was itself dreamed up by an engineering student. Though floating bridges are rare in the world, Oregon’s neighbor to the north is considered the global home of the floating bridge. They are an option when a body of water is too deep to effectively employ columns, as is the case with Lake Washington, which has an average depth of 108 feet and a deepest point of 214 feet. Floating bridges can work if the water is a relatively stable level and lacking strong currents and ice floes, as a young engineering student, Homer Hadley, reasoned about Lake Washington nearly 100 years ago.

Hadley’s plan was finally put to use in 1940 with the construction of the Lacey V. Murrow Memorial Bridge. The Murrow bridge’s companion span was named for Hadley upon its completion in 1989. Rail was envisioned to cross Lake Washington as far back as 1976, when a pact was signed to add high-capacity transit to the bridge. But it wasn’t until Seattle was squeezed by development in the mid-2000s that testing began. The Washington State Department of Transportation put together a panel including engineers of all stripes that identified 23 issues designers would have to account for in their final plans.

They anticipated problems with corrosion, wind, lightning, maintenance, attachments for the tracks to the bridge pontoons and structural impacts to the bridge, to name a few.

After the constantly changing lake levels, the next great challenge for the UW team was attaching rails to the bridge pontoons without use of bolts (a condition of the Federal Highway Administration was to not add holes to the bridge.) This meant traditional methods of building rail could not be considered.

After puzzling through various trials, Sound Transit’s engineers decided to use layers of various adhesives between the bridge decks and rails. But the adhesive solution has be able to withstand extreme vibration and shrinkage from the curing process.

When Sound Transit’s initial attachment solution appeared insufficiently flexible, former UW student Matthew Sisley wrote reports to Sound Transit. Using his notes, they changed course. Three years later, Tsvetanova is leading a team testing the final prototype, which has been informed by the earlier UW test results.

Though the students weren’t all paid or given school credit for their work, it was as real as can be, Stanton said. The students will have the same pride traveling over the bridge in a light-rail car as any other team member. Beyond that, firms that rely on Tsvetanova daily have taken note not just of her technical ability, but her ability to lead others by way of a clear and persuasive passion for the project, Stanton said.

“In fact, they’ve been leaning on me a lot, saying, ‘When is she going to graduate? I want to employ her.’”

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