Tuesday, January 15, 2008
Gusset Plates Critical Factor
In I-35W Bridge Collapse
Undersized gusset plates in the Interstate 35-W bridge in Minneapolis were "the critical factor" in the bridge collapse last year that killed 13 people and injured 100, 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."
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.
The findings are consistent with what the NTSB said about a week after the Aug. 1 collapse, in which the bridge plunged into the Mississippi River. At the time, the NTSB said it had found issues with the collapsed bridge's gusset plates, but expected a full investigation to take more than a year.
...investigators found 16 gusset plates that were fractured, said one of the officials. Eight of the plates were in the location on the south side of the bridge where the collapse began, according to that official.
The fractures prompted engineers to calculate whether the plates were adequate to hold the bridge together. What they found was that the half-inch thick plates should have been an inch thick — double the size.
The findings suggest that bridge inspectors, who are required to regularly check for signs of wear or cracks, did not miss any problems on the Minneapolis structure, an official said.
In related news, When reporting on any story about the I-35W Bridge Collapse, Minneapolis-St. Paul local television station, WCCO - a station whose liberal slant is obvious and apparent in every newscast - has a graphic that reads THE BRIDGE - - - like this:
- - - with the center of letter "I" missing. Isn't that clever? Isn't that pathetic?
The other irony is - and this applies to all media, especially the local media - that no coverage of the collapsed bridge is reported on without accompanying video footage of the fallen bridge and the aftermath.
And yet - somehow - the media almost never shows footage of the September 11, 2001 attacks. The bridge calamity? Oh, they'll run that footage endlessly.
No - no intentional bias here.
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