Design Flaw Cited in I-35W Bridge Collapse

According to NTSB findings released today,a design error which led to undersized gusset plates being used in the construction of the I-35-W bridge in Minneapolis contributed to it's collapse last year. 13 fatalities 100 injuries were the result of this oversight.

NTSB Chairman Mark V. Rosenker said the gusset plates, which connected steel beams, were roughly half the thickness they should have been. Investigators found 16 fractured gusset plates from the bridge's center span, he said.

Rosenker said the agency's investigation found no evidence that cracking, corrosion or other wear "played any role in the collapse of the bridge." They also found no flaws in the steel and concrete material used in the bridge.

The Minneapolis bridge was a steel-deck truss bridge that opened in 1967. Rosenker said it wasn't clear how the design flaw made it into the bridge because investigators couldn't find the design calculations.

There are about 465 other steel-deck truss bridges around the country. Rosenker said the safety board had no evidence that the deficiencies in the Minneapolis bridge design "are widespread or go beyond this bridge."

But he cautioned that states and contractors should look at the original design calculations for such bridges before they undertake "future operational changes."