"The critical factor" in the bridge collapse last year that killed 13 people and injured 100 on Interstate 35-W bridge in Minneapolis, Minnesota, were undersized gusset plates, the National Transportation Safety Board said Tuesday.
Chairman Mark Rosenker said the plates, which connected steel beams, were roughly half the thickness they should have been because of a design error. Investigators found 16 fractured gusset plates from the bridge's center span, he said.
"It is the undersizing of the design which we believe is the critical factor here. It is the critical factor that began the process of this collapse. That's what failed," Rosenker said.
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. Once they made it into the completed bridge, he said, there was little chance they would be noticed by inspectors.
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."
The Minneapolis bridge was deemed "structurally deficient" by the federal government as far back as 1990, and the state's maintenance of the structure has been questioned. But Rosenker said the NTSB investigation has found no evidence that cracking, corrosion or other wear "played any role in the collapse of the bridge."
In his update Tuesday, Rosenker also noted structural weight had been added to the bridge in two major renovations, as well as construction materials that were on the bridge the day it collapsed as part of a resurfacing project.
Source:Xinhua
|
Comment
Tell A Friend
Print Format
Save Article