Construction materials probed in Minnesota 2007 bridge collapse

Safety investigators said more than a half million pounds of construction materials had been piled on the Interstate 35W bridge directly above steel plates on the day they failed, causing the Minneapolis bridge to collapse.

Investigators told the National Transportation Safety Board that workers had begun stacking material on the bridge in July. By Aug. 1, 2007, the stockpile had stretched onto the span that initially gave way.

During that evening’s rush hour, the bridge shuddered and then tumbled into the Mississippi River, killing 13 and injuring 145.

Investigators say the thickness of the steel plates was the key problem, but they will offer a safety recommendation for the board to approve regarding storing of construction materials on bridges.