MnDOT keeps close eye on bridges over Mississippi
The Highway 43 bridge in Winona, previously marked "structurally deficient", has more behind its numbers than what it may seem.
WINONA — The Minnesota Highway 43 bridge in Winona has been classified as "structurally deficient" since 2010, but officials say the bridge is safe.
Construction began last year on a 5-year, $162 million project to build a new span across the Mississippi River and then renovate the existing structure, with completion in 2019 or 2020.
The bridge was inspected this month; also being inspected this month are the the Michael Duane Clickner Memorial Bridge in Wabasha and the Red Wing Eisenhower Bridge .
The report from the Winona bridge 's latest inspection is still being finalized, but "there were no significant findings, no critical findings," said Craig Lenz, Minnesota Department of Transportation district bridge engineer. "We're observing the same type of deterioration, but it's not a significant progression from last year."
The reports from inspections done in June 2014 show that the Winona bridge's ratings were the lowest of the three.
Each bridge receives an appraisal rating based on structure, and a conditional rating based on deterioration levels, on a scale from 0 to 9. According to an MnDOT manual, both ratings evaluate the bridge as "compared with a new bridge built to current design standards."
In 2014, only the Winona bridge had multiple numbers that fell at or below a five. As a rule of thumb the ratings can be considered in three groups: poor (1-4), fair (5-7) and good (8-9).
In the 2014 condition rating for the Winona bridge, the deck is a five, and the superstructure as a four.
A bridge also has a sufficiency rating, which takes into account "the structural adequacy, functional capacity, and essentiality for public use."
In 2014 the sufficiency rating for the Winona bridge was 24.3 percent out of 100 percent, while the Red Wing bridge received a 43.8 percent and the Wabasha bridge received a 74.5 percent.
According to the December 2014 National Bridge Inventory, 830 of the 12,961 bridges in Minnesota are structurally deficient. It means that "the bridge is safe but in need of repair, closer monitoring or weight restrictions so that it does not become unsafe."
"If we ever observe anything that would make a bridge unsafe, we'd close it as fast as we could," said Lenz. "And we've done that before."
With the new Winona bridge being built, Lenz is often asked if something is wrong with the current bridge or if it is safe. He reassures people that it is; "We haven't had any new critical findings. If we ever find any, we will close the bridge. We keep it open as long as we consider it safe for legal loads."
The current Winona bridge is eligible for the National Register of Historic Places, which registers "places worthy of preservation." Once the new structure is completed and Highway 43 traffic is switched to it, the existing bridge will be rehabilitated and reconstructed.
Winona, along with the Red Wing and Wabasha bridges, receive a routine inspection every 12 months and a fracture critical inspection — a type of in-depth inspection — every other year. These bridges also receive underwater inspection on a 48-month cycle.
A routine inspection covers "every major aspect of the bridge" — the deck, superstructure, substructure, and the culvert — and is conducted using a snooper truck — an under bridge inspection vehicle that allows for difficult areas to be inspected and/or repaired.