The collapse of the St. Anthony Bridge in Minneapolis started with a design flaw in the gusset plates, confirming suspicions that arose in the first week of the investigation. A source familiar with the conclusion told CNN earlier this morning that the NTSB will announce that finding later today, ending speculation that poor maintenance caused the deaths of 13 people last August:
Federal investigators have identified a design flaw as the cause of last year’s Interstate 35W Minneapolis bridge collapse that killed 13 people, a congressional official said Tuesday.
The official, who was briefed by the National Transportation Safety Board, said that investigators found a design flaw in the bridge’s gusset plates, which are the steel plates that tie steel beams together.
The official spoke on the condition of anonymity so as not to pre-empt an update being provided later Tuesday by the NTSB chairman, Mark V. Rosenker.
The findings are consistent with what the NTSB said about a week after the August 1 collapse, in which the bridge plunged into the Mississippi River.
Within hours of the collapse, some critics here and nationwide pointed to the collapse as the end result of underfunded infrastructure. One local crank blamed the head of the Taxpayers League of Minnesota for turning bridges into deathtraps six hours after the bridge failed. Others demanded a gas-tax increase to bolster the $2.2 billion annual budget for MnDOT, the agency which spends three times more than the budget for public safety every year.
Instead, we find out that the bridge design doomed it from the start. The bridge was built in a post-war period where streamlining and efficiency created a lot of questionable bridge designs; a few years later, engineers returned to the more robust pre-war concepts. This collapse showed why that was necessary, and it serves as a warning to those who skimp on redundancy as unnecessarily costly in building infrastructure.
Minnesota has already begun building the replacement bridge, which we hope will be complete by the end of the year. Everyone can learn lessons about this bridge collapse, especially those who attempted to exploit it for their own political agendas.
UPDATE: USA Today has more:
In the wreckage of the I-35W bridge, 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.
And without a redundant support structure, once the first gusset plate fractured, the rest would have failed as the weight of the bridge shifted and generated momentum.