Bridge collapse cause will send states scurrying

The National Transportation Safety Board today said the gusset plates — steel plates that attach several different components — were responsible for the collapse of the I-35W bridge over the Mississippi River in Minneapolis last August. Read the full report here (pdf). That pretty much confirms what many of the media reports said — reports the NTSB dampened — in the aftermath of the bridge tragedy.

But here’s the thing: the bridge was built as it was designed. The problem is the design was flawed and the NTSB investigator said there are over 400 bridges across the United States designed the same way.

That’s bound to get the attention of transportation officials all across the country (perhaps even around the world), many of whom adopted a “it can’t happen here” attitude in the wake of the bridge collapse, even when gusset plates were first mentioned as a possible cause.

“The issue is underdesign,” said NTSB chair Mark Rosenker, who wants states to recalculate the design of similar bridges.

“We’ve never seen anything like this, nor anticipated anything like this,” he said. “Gusset plates are usually the most robust parts of a bridge… Why didn’t we find it 10 years ago? No one in the hundreds of years of bridge design had found that a gusset plate that was underdesigned and thereby caused a collapse. It was not something people recognized as a weak point.”

“We do not believe it’s a systemic problem in the United States with regard to bridges, but we feel it’s critical we share it with the industry so that we can guarantee there isn’t something we don’t know about.”

Still unknown, however, is what was “the straw that broke the camel’s back,” Rosenker said. “What was different on August 1st.” They think they know what gusset plate failed first, triggering the collapse. They just don’t yet know why.

The revelation counters all attempts by the NTSB to dampen focus on the gusset plates when it first sprouted as a possible cause a week after the collapse. At the time, an NTSB spokesman called media reports “overblown.”, and going so far as to say the plates were not a problem.

The company that designed the bridge was Sverdup & Parcel.

For his part, Gov. Tim Pawlenty used the occasion to launch a broadside against political opponents and reporters:


“Since the bridge collapse, I have encouraged politicians and members of the media not to make judgments about the cause of the collapse until the NTSB investigation is complete. Unfortunately, my suggestion was not widely followed.

“Some individuals have leapt to premature conclusions. The NTSB clearly stated today the original design flaw was unrelated to subsequent inspections or maintenance of the bridge.

“Again, while the NTSB investigation is not complete, the focus of the investigation appears headed in a direction different than many of the political claims that have been made. It is our hope that at least now people will reserve further judgment until the investigation is complete and that we strive to address these matters in a fair, factual and non-political manner.”

MPR’s Sea Stachura will have reports tonight on All Things Considered and tomorrow morning on Morning Edition.

Update 3:53 p.m. Transportation Secretary Mary Peters has now sent an advisory to transportation officials in other states.

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