The fatal failure of the Interstate 35W bridge in Minneapolis began with a design flaw in the steel plates in a main trust which collapsed. A major contributing factor was the 287 tons of construction materials stored on the bridge.
This design flaw went undetected for more than 40 years.
The National Transportation Safety Board found that the bridge engineers failed to properly calculate the proper thickness for the gusset plates on the bridge.
The I-35W bridge was a "fracture critical" structure. Bascially, the failure of any part of the bridge would bring down the entire structure.
On Aug. 1, 2007, overstressed by the additional tons of construction material and rush hour traffic, the I-35W's center span first swayed, then collapsed and pulled down other sections into the Mississippi River.
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The final result: 13 people killed and 145 injured in the bridge collapse.
Minnesota and other states have worked to improve bridge inspections. This is no easy task considering the multitude of bridges across America. The state has already closed the state Highway 23 bridge in St. Cloud and has started the replacement process on it.
Certainly, the benefit of this tragedy now is better and more frequent inspections. The additional benefits include better attention to sophisticated engineering techniques used in bridge construction and more utilization of bridge monitoring equipment.
We hope this tragedy will not be in vain and that future lives will be saved by the better inspection and engineering.
