Skagit County isn’t the only place where people are erecting temporary steel bridges this week.
Engineering students from 49 universities will participate Saturday at the 2013 National Student Steel Bridge Competition, at the University of Washington — nine days after the dramatic collapse of a truss span 62 miles north.
The teams will quickly assemble their bridges while avoiding missteps into an imaginary river. Winners are chosen based on the fastest assembly time, lowest bridge weight and strength tests.
The bridges, about 20 feet long, must withstand 1,500 pounds placed on the main span, plus 1,000 pounds on a cantilevered segment that’s unsupported from below.
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On May 23, a steel-truss span on Interstate 5 buckled and fell into the Skagit River, when a truck with a tall load struck overhead crossbeams. Two vehicles with three people fell into the river, but nobody was seriously injured. Workers have begun assembling a temporary freeway span.
“It raises awareness for civil engineering,” said UW engineering professor Jeffrey Berman of the Skagit incident.
He said “99.9 percent” of engineered structures work fine, and today’s students have a duty to maintain quality. “These are the future unheralded heroes of society, as far as having transportation, clean water, safe structures.”
Seattle is a treasure trove of trusses, from the seismic braces in Pioneer Square brick buildings, to the retractable roof of Safeco Field, to the Ship Canal highway bridges. Despite advances in concrete girders and cable-stayed spans, the truss remains important even for highways, said Berman.
“If the I-5 Ship Canal Bridge and the Aurora Bridge were built today, they would still be truss bridges,” he said.
Most teams showed off their bridges Friday afternoon in Red Square, before disassembling them in advance of Saturday’s competition.
UW’s team devised a three-dimensional “space truss,” where the load won’t rest on single beams, but a triangular prism of thin rods — envision two Toblerone chocolate bars in parallel. The shape is stable and requires few crossbeams.
“We have less than 30 pieces on this bridge, while other teams have more than 50,” said UW student Francesca Renouard.
University of British Columbia’s black bridge was still tacky from a last-minute paint job after the team hurried south Friday, with barely enough time to gawk at the Skagit bridge’s gap.
Université Laval of Quebec, site of a famous cantilever bridge collapse during construction in 1907, brought wood bracing to temporarily support its model bridge during assembly. Alexandre Drouin disliked a question about yesteryear.
“They don’t build bridges anymore like you did in the 1900s” — but he said Laval does show footage from Tacoma about the first Narrows Bridge falling in 1940.
A sentimental pick is George Mason University of Virginia, new in the finals, which lacks the facilities the other teams have to fashion lightweight custom rods. GMU’s green-and-gold, 400-pound creation is twice as heavy as others, borrowing surplus steel from a local contractor. And on Friday it was the only overhead truss — like the I-5 Skagit River bridge — on display in Red Square.
“This is a great competition,” said GMU student Zachary Malone. “It’s a great way of moving your calculations from the classroom to the real world.”
Saturday’s competition runs from 8 a.m. to 4 p.m., at Hec Edmundson Pavilion.
Mike Lindblom: 206-515-5631 or firstname.lastname@example.org.
On Twitter @mikelindblom