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Blatnik Bridge status upgraded to 'adequate'

Blatnik Bridge (2016 file photo / News Tribune)

An inspection last summer has upgraded the Blatnik Bridge between Duluth and Superior from deficient to adequate, but it doesn't change the long-term future of what is referred to as "the high bridge."

"We're still thinking the same thing," said Duane Hill, the Minnesota Department of Transportation's district engineer in Duluth. "We still need to do something."

The 56-year-old bridge has been targeted for replacement by the local MnDOT office by as soon as 2028. The status upgrade is owed to three rounds of gusset plate reinforcement which ended in 2016.

What replacement looks like for the bridge remains unclear. It could mean a new bridge built alongside the old one, Hill said, or it could mean a rebuilt Blatnik Bridge which incorporates sound elements from the current bridge.

"The first thing we're doing is more of an assessment of the existing bridge to see if we could use parts of the existing bridge," Hill said, describing plans for this summer.

In order to help determine the course, Hill is in the process of hiring a new engineer to take the lead on the project.

Ongoing planning for the more immediate reconstruction of the Twin Ports Interchange, or "can of worms," through Duluth and some smaller projects throughout the district means "the staff is full," Hill said. Hill oversees major highway and bridge projects throughout MnDOT's District 1 — from Pine City to International Falls and throughout the Arrowhead region of Minnesota.

The new engineer will spend 60 percent of a full-time job devoted to the future of Blatnik, Hill added. Across the bridge in Superior, the Wisconsin Department of Transportation is conducting an ongoing traffic survey for U.S. Highway 53 from East Street to the Blatnik approaches. The survey isn't directly related to Blatnik work, but the data could be useful, said Jessica Felix, WisDOT's deputy director in Superior.

"That work is not driving the survey," she said, "but we might use the data to look at a no-build option — to look at traffic count and what kind of volume we're seeing."

The nine-month survey was specifically ordered, she said, to address a documented crash history at the East Street intersection with Highway 53, which carries over the four-lane Blatnik Bridge as Interstate 535.

The data collected in the WisDOT survey wouldn't be useful for a new bridge option, she said, since approaches in that scenario would change dramatically.

In an arrangement between the state agencies, WisDOT manages the Bong Bridge farther south off Interstate 35, while MnDOT takes the lead on the Blatnik Bridge. Costs for border bridges are shared between states.

Prior to the results of last summer's inspection, the Blatnik Bridge was rated as structurally deficient.

"We had a problem and we fixed it," Hill said, referring to the series of gusset plate reinforcement efforts in 2008, 2012 and 2016 that corrected thinning and corroding spots in gusset plates. "Our goal for managing this bridge is managing it to the point we don't have to do any service interruptions. When we find something that makes us nervous we try to do the improvements right."

The Blatnik Bridge is already scheduled to receive $9.1 million in repainting, maintenance and necessary repairs in 2020.

This summer, MnDOT will analyze the existing trusses with the help of a consulting firm. Additionally, MnDOT plans to take a look at all of what Hill called "the substructure," which includes the piers, abutments and concrete pier caps.

Every four years, MnDOT does an underwater check of the pilings and such. But most of the bridge's piers are over land, and the agency wants to check how the steel is holding up where it contacts with soil.

"Are there problems with the steel right at the interface with piers and the soil?" Hill said. "There are many, many spans and most of it is over land. We're going to be looking at those things this summer."

Finally, in the 1990s, the bridge deck was widened using beams and post-tension technology from the time, which was then grouted over.

"Over time the technology has changed," Hill said. "We want to know how it's performing. Is the steel still sound? Is it corroding or not in the grout? We're going to open up a couple of those areas to see what we can learn."