Traffic changes and construction will become commonplace as crews prepare the Washington Avenue bridge for the Central Corridor light-rail line by 2014.
In order to support a 106,000-pound light-rail vehicle, crews are adding two additional columns on each pier and four trusses to the 46-year-old bridge.
Weeks after the collapse of the I-35W bridge in 2007, a Central Corridor Management Committee study found that the Washington Avenue Bridge was “fracture-critical,” meaning if one part of it failed, the rest was susceptible to collapse.
The I-35W Bridge was described as fracture-critical in a recently published book by several University of Minnesota faculty members titled, “The City, the River, the Bridge.”
University civil engineering professor Roberto Ballarini devoted a chapter in the book to the failure of a single gusset plate that was built too thin, citing it as a major factor in the collapse. Added weight from construction equipment contributed to the disaster.
Tom Fisher, dean of the College of Design, discussed the concept of fracture-critical designs in the book. He said bridge designers have learned about the perils of such designs in recent decades, and the I-35W disaster was a stark reminder.
“The engineering community has really learned the lesson of the I-35W Bridge,” Fisher said.
But the two bridges have very different designs and there’s little worry of a collapse on Washington Avenue, said Ted Galambos, a professor of emeritus at the University’s civil engineering department who specializes in structural engineering.
Galambos said that although the Washington Avenue Bridge is currently safe, in the aftermath of the I-35W Bridge collapse engineers are going to add more than enough support and strength to it.
“They’re going to beef this up,” Galambos said.
The bridge underwent minor construction in 2008 to reinforce the pedestrian deck, but that work was independent of the light-rail construction.
Traffic has been restricted to one lane in both directions on the north side of the bridge for about a year. Last week, crews began determining how to best remove the roadway on the south side, according to project spokeswoman Laura Baenen. After replacing the south side lanes, they will redo the north.
Traffic won’t be completely halted on the bridge during construction except on rare occasions and with plenty of public notice, Baenen added.
The bus stop in front of Blegen Hall has been moved west, and the stop is one-third the size, according to Parking and Transportation Services spokeswoman Jacqueline Brudlos. She added that buses are still running on time despite the restrictions.
Construction on the East Bank campus is set to begin in May, when crews will begin to turn Washington Avenue into a pedestrian roadway and eliminate vehicle traffic.