State inspections of truss bridges find no repeat of I-35W gusset problem

With Thursday’s National Transportation Safety Board report on the I-35W bridge collapse expected to blame in part inadequately designed gusset plates, it’s good to know that state inspections of the 25 truss bridges in the Department of Transportation system have not found similar deficiencies.

That’s what MnDOT officials told the state House of Representatives Transportation Finance Committee today, according to the state House Information Services. 

MnDOT’s take on the testimony is here.

House committee members learned that all 25 trusses on the MnDOT bridge system were load-rated by July 1 to verify the original design was correct. Inspection of gusset plates on the 25 structures was completed one month later.

Some actions were taken after the inspections, including the closure and rebuilding of the DeSoto Bridge in St. Cloud, stiffening of gussets to restore full safety factors on the Blatnik Bridge in Duluth, gusset reinforcement because of corrosion on the Winona span and strengthening of gusset plate edges on the Hastings bridge to meet design code requirements.

MnDOT also has established eight additional positions to help with fracture-critical bridge inspections.

Officials said state bridges are inspected once every two years, or if bridge conditions are found to be low-rated, annual inspections are required. Underwater bridge inspections are required every five years.

And the Associated Press reports that state bridge engineer Dan Dorgan also testified that Minnesota’s bridge inspectors are getting more high-tech equipment to help them assess the condition of bridges. He said the gear includes ultrasonic and magnetic equipment to test for corrosion and cracking in metal.

And they’ll add ground-penetrating radar to help inspectors test bridge decks for concrete separation without displacing traffic, rather than the current method of closing lanes and dragging a chain across the bridge deck.

Dorgan is also looking into technology that would let inspectors look at photos and notes from past inspections when they’re in the field examining a bridge.

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