Tuesday, 15 January, 2008, Federal Investigators announced that a "serious design error" was a key factor behind last summer's deadly collapse of the Interstate 35W's Minnesota bridge. The bridge collapsed on 1st August 2007 killing 13 people and injured more than 100 people. Routine bridge inspections will not likely discover the failure. , but also said that the mistake would not likely have been discovered during routine state inspections.
The bride had been built with gusset plates - the steel parts that connect the girders, which support the bridge. Investigators found that the gusset plates were too thin to hold up the bridge with increased traffic and additional weight of infrastructure improvements.
Investigators have found 16 fractured gusset plates from the center section of the steel-deck truss bridge. The thickness of the gusset plate was about half the required thickness to carry present day loading.
The bridge was built in 1967 and after 40 years of service, the bridge was modified to carry more traffic by increasing the driving deck thickness.
The bridge was designed by Sverdrup & Parcel, a Missouri-based civil engineering firm. The company was later bought by Jacobs Engineering Group Inc. in Pasadena. At the time of the bridge's collapse, maintenance crews were using tons of equipment and construction material on the bridge's deck thus putting additional strain on weaker spots on the bridge and finally gave way into the Mississippi river.
