State’s second-longest bridge up for repairs

A project that includes fixes to Duluth’s Blatnik Bridge, the second-longest bridge in the state, is scheduled to begin this summer, even as the Minnesota Department of Transportation strategizes about the bridge’s long-term future.

St. Michael-based PCi Roads put in the apparent low bid of $1.939 million Friday for the upcoming project, which includes repairs to 23 gusset plates and pavement fixes on Interstate 535. The bid came in well below MnDOT’s $2.8 million estimate.

The nearly 8,000-foot-long bridge carries I-535 over the Saint Louis Bay between Duluth and Superior, Wisconsin. Its neighbor to the south, the 8,395-foot-long Highway 2 Richard I. Bong Memorial Bridge, is the longest bridge in the state.Repairs on the Blatnik Bridge will begin in mid-August and continue through late October, according to MnDOT.

MnDOT District 1 bridge engineer Kevin Rohling said the 55-year-old bridge has been getting frequent maintenance in recent years, including steel repairs in 2008 and 2012 and evaluation of suspender cables in 2010.

Like the Interstate 35W bridge that collapsed in Minneapolis nine years ago, the Blatnik Bridge was built with a “fracture critical” design, which means that if one critical component were to fail, the entire bridge could collapse.

Rohling emphasizes that the Blatnik Bridge is safe to drive on.

“It’s just that if we allow this deterioration to continue, at some point it could become unsafe. And we don’t want to get to that point,” he said.

MnDOT says on the project webpage that it has 123 fracture critical bridges in its current inventory. When they are up for replacement, the bridges are built with “redundant designs,” MnDOT said.

A recent inspection found that 23 of the bridge’s gusset plates need repair or replacement. One of those plates has a crack that affects its structural integrity, and others have “varying degrees of corrosion,” MnDOT said.

Gusset plates are the steel plates that help connect bridge elements. A 2008 report from the National Transportation Safety Board concluded that the failure of undersized gusset plates contributed to the collapse of the I-35W bridge.

Undersized gusset plates aren’t a concern on the Blatnik span, Rohling said. The main concern is that the amount of corrosion on the gusset plates has “accelerated faster than we would like to see,” and it needed attention right away, he said.

Overall, MnDOT has increased its inspection efforts since the I-35W bridge collapse, and gusset plates are “one area we have been focusing on,” he said.

Besides Blatnik’s gusset plates, crews will repair or replace a diagonal floor beam, replace bolts and install new navigation lights.

Meanwhile, MnDOT is working on a plan to “schedule appropriate maintenance, preservation, rehabilitation, and ultimately replacement” of the Blatnik Bridge. The plan is scheduled to be finished by the end of this year, Rohling said.

MnDOT doesn’t know precisely when the bridge will need to be replaced, but the best guess is that it will be between 15 and 40 years from now, Rohling said.

“We are not committed to that time frame. That is kind of what our thoughts are,” he said.

Tim Worke, director of the Associated General Contractors of Minnesota’s highway and transportation division, estimates that it would cost “hundreds of millions of dollars” to replace the bridge.

Worke said in an email that there are “multiple issues on both ends” of the bridge that would need to be addressed “in addition to just replacing the structure itself.”

“The Blatnik is a crucial artery to interstate commerce in the Duluth-Superior area, so it deserves a high level of attention,” he added.

The bridge carries about 22,800 vehicles per day and rises 120 feet above the Saint Louis Bay.

The repair will require some lane closures. Some of the traffic will detour to the Highway 2 Richard I. Bong Memorial Bridge, MnDOT said. Ramps will close periodically.

Chippewa Concrete Services was the only other bidder on the repair project ($2.33 million).