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Bridge collapse probe focuses on unexplained shift

by EdH / August 3, 2007 10:42 PM PDT
LINK

Maybe NOT Bush's fault after all? Maybe not time to panic after all?

MINNEAPOLIS, Minnesota (CNN) -- Investigators trying to figure out what caused Wednesday's massive bridge collapse are focusing on the southern end of the span, which "behaved differently" as it fell, the National Transportation Safety Board said Friday.

The NTSB, which is investigating the disaster that killed at least five people and injured dozens, is also hoping another video provided by the Army Corps of Engineers will provide new images of the collapse.

What's getting investigators' attention is the way the southern part of the bridge fell in a video they've already examined -- recorded by a security camera near the bridge's north end -- and the way the section settled after the collapse.

"It appears that it has shifted approximately 50 feet to the east and when we compare that to what we've seen in the rest of the bridge -- the rest of the bridge appears to have collapsed in place, " said NTSB Chairman Mark Rosenker, who is leading a 19-member team charged with determining the cause of the accident.

"We're going to take a look at any unique design factors that could have created that shift...for whatever reason."


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Well
by duckman / August 3, 2007 11:14 PM PDT

I think I heard about Randi Rhodes from (dead )Air America that she was blaming Bush. That's how the chickens come home to roost.

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Nay, it's Kevin Bacon's fault
by Diana Forum moderator / August 4, 2007 12:22 AM PDT
In reply to: Well
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Supposedly a freight rain was passing underneath
by Steven Haninger / August 4, 2007 12:33 AM PDT

at the time of the collapse. I have to wonder if its rumbling near support structures will be considered a possible trigger. Trains make the ground shake around them.

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Also, jackhammers used on the resurfacing project...
by Dave Konkel [Moderator] / August 4, 2007 1:16 AM PDT

might have played a role. What would be particularly stressful would be if the frequency from the jackhammers happened to be the same as the frequency from the train. Such hHarmonic vibrations" are often a problem in amplyifying stress synergistically; that's why marching troops always break cadence when crossing a bridge.

-- Dave K, Speakeasy Moderator
click here to email semods4@yahoo.com

The opinions expressed above are my own,
and do not necessarily reflect those of CNET!

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Marching troops breaking cadence on bridge...
by J. Vega / August 4, 2007 3:10 AM PDT

I have heard the tale of Marching troops breaking cadence on a bridge and wondered about it. Researching it all I was able to find for it's start was the case of the Broughton Bridge in 1829 which some blamed on marching troops.
Getting more current in the case of harmonic vibrations and bridge disasters there is the case of the Tacoma Narrows Bridge collapse in 1940 (AKA Galloping Gertie). Those two cases do have something in common, they were both suspension bridges. But in the case at hand the bridge was not a suspension bridge.

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Hi J....
by Mac McMullen / August 4, 2007 3:59 AM PDT

As I recall, way back in the military days, troops were ordered to "extend ranks" and march "at ease" on a bridge structure, deliberately breaking cadence to preclude the "weight and vibration" of simultaneous pounding feet.

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The Discovery TV channel or
by John Robie / August 5, 2007 4:24 AM PDT

maybe it was one of the History TV channels, or A&E, some time back in one of their hour long programs concerning bridges said it was discovered that the Tacoma 1940 'Galloping Gertie' was a design flaw that engineers did not know about at that time. The structure under the road surface of the bridge would catch the wind a certain way and the 'galloping' would start. All bridge designers learned from that experience and designed a different under structure for suspension bridges.

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Following that line of thought.......
by Mac McMullen / August 4, 2007 4:03 AM PDT

IF the sub-structure support on the east side failed, tipping the structure to the east, forcing the remaining stronger sub-structure to "lean" to the east would account for such a "shift".

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Kind of what I was thinking...
by EdH / August 4, 2007 9:32 PM PDT

If the river undermined the aupports of the bridge just a little....

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