Bridge Collapse Caused By Design Flaw, Not Maintenance

Captain's Quarters ^ | Jan. 15, 2008 | Ed Morrissey

[jdm]

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, architects 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.

[Emperor Palpatine]

Often design flaws take years to show up or even decades. When the Silver Bridge collapsed in Gallipolis, Ohio back in the 60's it was caused by a tiny crack in an I-Bar suspender that was there since the bridge was built in the late teens.



Lockheed built a turboprop airliner called the Electra in the late 50's that at the time was one of the most thoroughly tested planes ever built. They flew flawlessly in service for several years until the wings started to tear of several planes in flight killing hundreds. The design flaw was failure to isolate engine vibrations in wing spars. Lockheed fixed the problem and the plane continued to fly successfully. The military variation of the Electra is the P-3 orion and still flies to this day.



Some bridge engineer somewhere is about to lose his license, I'd wager.

[Donald Rumsfeld Fan]

[OESY]

Gusset plate and rust damage (not the St. Anthony Bridge in Minneapolis)

.

[Pilsner]

Some bridge engineer somewhere is about to lose his license, I'd wager.

If the bridge was built in 1967, I doubt the head engineer is still alive, much less licensed.

I once read a comment by a science fiction writer that mankind would never set sail to the stars, unless it had a faster than light (FTL) drive. His theory was simple: Without FTL, it will take generations for star ships to got to other planetary systems, and return. Only the government can afford to build such a space ship, and government officials cannot be trusted to oversee a massive construction project, if the government officials know that they will have been dead for a couple of lifetimes before their incompetence, or corruption, is discovered.

[17th Miss Regt]

steel must become molten before it loses its tensile strength and collapses.

...and as we all know, fire has never melted steel. (R. O'donnell, PhD, Structural Engineering and Donut Consumption)

[Donald Rumsfeld Fan]

They said the calculations were wrong. The error may have been in one of several stages—design, drafting, etc., I can’t remember exactly. The calculations were not reviewed after the point at which the error occured.

That's gonna hurt.

Speaking as a retired design engineer.... 'those kind of things damage engineering careers'.

Question for any structural engineers: Isn't it SOP to load test any new designs?

[B4Ranch]

[Steve_Seattle]

Since that bridge collapsed, I’ve seen numerous references to it in columns and letters-to-the-editor, usually - you guessed it - blaming Bush. One of the most recent was a snide reference in a column by Seattle Times columnist Joni Balter, who over the years has morphed from a reasonable liberal into a stinking, lying pig.

[Abigail Adams]

Thanks! Looks like U-10 is on the south side of the bridge, near Pier 6 and over the water.

I wonder where the construction equipment and material was located at the time?

[Myrddin]

Identifying the problem as a design flaw instead of negligent maintenance is going to pull all the justification for tax increases for more maintenance. The lefties are going to get very shrill if they can't raise taxes.

[Abigail Adams]

They don’t know in which stage of design the error occurred. It is hard to believe these calculations aren’t checked and rechecked a few times along the way.

[Between the Lines]

Yet amazingly, this flawed bridge stood for what? 50yrs?

It stood for 40 years. It was designed to last 50 years, but that was with four lanes of traffic. Not the eight lanes that it carried since the four shoulders were converted to traffic lanes in 1988.

[Between the Lines]

This is total BS. It is an attempt to sweep the entire thing under the rug.

It has been long known that the bridges built during the original Interstate building program had flaws. I have no doubt that the bridge (indlucing the gussets) fully met design standards WHEN IT WAS BUILT. Since then we have learned a LOT more and the design standards have changed.

I tend to agree with you. In 1988, when the four shoulders were converted to traffic lanes, all calculations concerning the structural integrity of the bridge should have been done again. Why was this "design flaw" not spotted then?

[webheart]

I wonder where the construction equipment and material as located at the time?

Iraq? (/obvious (I hope)sarcasm)

[bert]

....architects returned to the more robust pre-war concepts....

If he can’t distinguish between an architect and a structural engineer one wonders if he knows the difference between his ass and a hole in the ground?

[Tatze]

1988?? Well then, its George H.W. Bush’s fault!

[Abigail Adams]

Excellent point!

[Between the Lines]

I found this in another article:

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.

Currently, such calculations are done for the entire bridge, but not down to the gusset plates, the official said.
http://www.foxnews.com/story/0,2933,322849,00.html

Now we know where the weakest link is.

[Abigail Adams]

Interesting article here, in hindsight:

http://www.nydailynews.com/news/us_world/2007/08/04/2007-08-04_hey_dont_blame_me_for_collapse.html

Snip:

The inspector who signed off on Minneapolis’ Interstate 35W bridge almost every year since 1994 refused to accept blame yesterday [August 3, 2007] for the collapse that killed at least five people.

“Go after the designer. Go ask him why he did what he did,” Kurt Fhurman angrily told the Daily News at his home. “Go after the designer.”

[festus]

Yup. Throw the original engineer under the bus, despite the fact that if the folks, including the latest engineers to approve the ongoing renovations, knew the thickness of everything and still went ahead and put large uneven loads on the structure.

Going to be a whole lot of arguing about these points for a long time.