Design error brought down that Minneapolis bridge

[Sea Skimmer]

Flaw ID'd in deadly bridge collapse
NTSB blames undersized plates in Minn. tragedy that killed 13
The Associated Press
updated 3:51 p.m. ET, Tues., Jan. 15, 2008
WASHINGTON - 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.
No nationwide deficiencies found
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.”
Investigators also found no flaws in the steel and concrete material used in the bridge.
Extra weight cited as well
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.
Transportation Secretary Mary Peters was expected to issue an advisory urging states to check the gusset plates when modifications are made to a bridge — such as changes to the weight of the bridge or adding a guardrail, said a federal official with knowledge of the plans. The official spoke on condition of anonymity because Peters had not yet made the announcement.
Currently, such calculations are done for the entire bridge, but not down to the gusset plates, the official said.
Stress advisory after collapse
Last August, Peters advised states to consider the additional stress placed on bridges during construction projects. An 18-person crew was working on the bridge when it collapsed.
Nearly three months later, she told a gathering in Washington of a “working theory” of a poorly designed gusset plate and a heavy load of construction materials.
Meanwhile, state lawmakers announced plans last month to spend up to $500,000 to hire legal counsel to aid in a legislative inquiry into the collapse.
Late last year, President Bush signed a massive spending bill which included $195 million to help replace the bridge. That came on top of the $178.5 million the federal government has already given Minnesota for the project.
The bridge was originally designed by Sverdrup & Parcel, a company acquired in 1999 by Jacobs Engineering Group Inc. of Pasadena, Calif. A message left by The Associated Press with Jacobs wasn’t immediately returned.
Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
URL: http://www.msnbc.msn.com/id/22663216/

[Admiral Valdemar]

What scares me more is, does this mean such other flaws exist in the tens of thousands of bridges in the US? I believe the American Society of Civil Engineers assessment of civil infrastructure was rated quite low only a few years ago, with many areas getting Ds. I can't recall what they said about bridges off the top of my head, but I'm guessing it wasn't better than the roads.

EDIT: Just found it.

Bridges C
Between 2000 and 2003, the percentage of the nation’s 590,750 bridges rated
structurally deficient or functionally obsolete decreased slightly from 28.5% to
27.1%. However, it will cost $9.4 billion a year for 20 years to eliminate all bridge
deficiencies. Longterm underinvestment is compounded by the lack of a Federal
transportation program.

[Androsphinx]

What scares me more is, does this mean such other flaws exist in the tens of thousands of bridges in the US? I believe the American Society of Civil Engineers assessment of civil infrastructure was rated quite low only a few years ago, with many areas getting Ds. I can't recall what they said about bridges off the top of my head, but I'm guessing it wasn't better than the roads.

Who the hell knows?

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.

[Einhander Sn0m4n]

That's fucked up. I'll bet the error was due to someone trying to save a few dollars of steel alloy per gusset plate. Dollars are funny things, really; one tends to pay for dollars in lives, as in this case.

Also, can someone edit out the huge number of unnecessary carriage returns in the quoted article? It's unreadable!

[Kuja]

The only thing left to wait for now is its appearance on an episode of Modern Marvels: Engineering Disasters.

[Jaepheth]

wouldn't it be easy to use a drill to test other bridges and see if the same problem is in any of the ones sampled?

or if that'd compromise structural integrity, couldn't they use something like subterranean sonar?

[Connor MacLeod]

We'll know if I die in another bridge collapse soon enough I suppose. There's a bridge a few block sfrom where I live that is supposedly nearly as old/similar design as the one that collapsed.

If for some reason you don't see me posting for several months, you can probably make a safe bet as to what happened

[Sea Skimmer]

wouldn't it be easy to use a drill to test other bridges and see if the same problem is in any of the ones sampled?

or if that'd compromise structural integrity, couldn't they use something like subterranean sonar?

Why would you use a drill to measure the thickness of an externally bolted steel plate? You could just walk up and use a ruler.

[CmdrWilkens]

The only thing left to wait for now is its appearance on an episode of Modern Marvels: Engineering Disasters.

Its like the nerd version of ESPN Instant Classics.

[Broomstick]

What scares me more is, does this mean such other flaws exist in the tens of thousands of bridges in the US?

Well, yeah, of course we have other defective bridges - we have a LOT of bridges, after all. This isn't the first bridge collapse, either, and I doubt it will be the last. No doubt some of those bridges have similar or identical flaws and it's only a matter of time before another collapses.

The question is, does anyone give enough of a damn to do anything about it? I my own area we've had at least 2 bridges torn down and replaced due to severe structural defects and we did it before anyone got hurt or killed. Yay, us. Problem is, even if you replace 9 or 99 bridges before anything bad happens if that 10th or 100th bridge goes down and kills people it's still a tragedy that you wished could have been prevented.

Between changing standards over the years, contractors who cheat/defraud, and the apathy of local officials in regards to infrastructure I expect in another 10 or 15 or 20 years we'll have a similar disaster.

What? Yes, I'm all cynical today, why do you ask?

[Jaepheth]

wouldn't it be easy to use a drill to test other bridges and see if the same problem is in any of the ones sampled?

or if that'd compromise structural integrity, couldn't they use something like subterranean sonar?

Why would you use a drill to measure the thickness of an externally bolted steel plate? You could just walk up and use a ruler.

I supposed they were encased in concrete. I guess I was wrong.