Inspectors pored over the John A. Blatnik High Bridge just a week ago. Yesterday transportation officials shut down one lane each direction on the span between Duluth and Superior.
The bridge is a more than mile long thoroughfare that lifts traffic high above the St. Louis River - high enough to let ships pass through. It might be best known for its view of the Duluth harbor and nearby Lake Superior, and the occasional high winds that howl in from Lake Superior causing a white knuckle drive.
Minnesota Department of Transportation Commissioner Tom Sorel said the bridge lanes have been closed until contractors can strengthen 16 gusset plates on the bridge. Those are the plates that hold steel beams in place where they meet.
"The gusset plates we are talking about are undamaged; however, recent load bearing calculations and field inspection discovered that these plates did not meet the load requirement," Sorel said. "The lanes will be closed today and remain closed until repairs are completed. Let me reassure you once again that the bridge is safe, or it would have been closed."
Sorel described the closure as conservative action, based on sound engineering principals. He said the work should be completed, and the bridge fully reopened by mid-June.
He said the bridge was just inspected last week, following an alert on gusset plate design from the National Transportation Safety Board. Minnesota began inspecting the gussets on all 25 bridges in Minnesota with that design.
According to MNDOT State Bridge Inspector Dan Dorgan, there are 16 plates total that will be strengthened with steel over the coming weeks.
"We identified two gusset plate locations where the safety factor that we were achieving with the gusset is not to the level that is what we set as standard and what we chose to achieve. The bridge is safe, it is just that the extra capacity over design loads isn't as high as what we are comfortable with," Dorgan said.
Officials stressed that the gussets in question are not damaged or severely corroded. But Dorgan said they were designed for a lighter load when this bridge opened in 1961.
"The gusset plate appears to be sized correctly for thickness. A couple of changes have occurred, however, in this bridge over the over 40 years in service," Dorgan explained. "When the bridge was re-decked in the early 1990's there was a major renovation on the Blatnik bridge at that time. The deck thickness was increase two inches at that time."
That additional thickness added weight the older plates weren't designed for by today's standards.
Officials said they've already relieved any safety concerns by removing half the traffic lanes. That not only reduced the load the bridge can carry, it puts the traffic in the middle of the bridge where the structure is strongest. At times, they say they will have to close another lane each direction, completely shutting off traffic in one direction.
Local motorists will have to travel a couple of miles further up the St. Louis River to cross on the other major bridge, the Richard A. Bong Memorial Bridge.
Area residents appear to be gratified that officials are looking hard at the bridge and taking swift action. Steve Betzler of Superior works in Duluth, and said he crosses the bridge twice every day. He said bridge safety has been on his mind.
"When the bridge collapsed in the Cities, it's the first thing that popped into my head, was, what would if that happened here," Betzler said.
Like many people, Betzler will just have to accommodate the inconvenience.
"Well now I know that I'll have to leave a little bit early, but besides that, at least they're doing something about it, you know," Betzler said.
Repairs begin immediately. MnDot officials said they had no estimate of the cost.
If they can hit their goal of reopening in mid-June, they'll have the bridge fully ready before the seasonal summer tourist season picks up.