Video: Sabo Bridge cables vibrate like guitar strings, July 2011

Categories: Transportation
Sabo bridge.jpg
TC Daily Planet
Video has surfaced of the Sabo bridge cables playing "The Wind Cries Mary."
On February 19, a cable support above the Martin Olav Sabo bike and pedestrian bridge gave way and slumped precariously over the Hiawatha LRT tracks, forcing temporary suspension of light rail service and closing Hiawatha Avenue. The bridge remains closed.

News of the bridge failure caused some to wonder whether Hennepin County made a mistake opting for such a "fancy" design. Anecdotes began circulating from folks who had seen the bridge's string-like cables fluttering in the wind.

Now, video has surfaced from last summer of those cables vibrating like a Hendrix-plucked guitar.

Earlier this week, the Star Tribune reported that engineers expressed concerns about the Sabo bridge's cable plates while the structure was being constructed. Officials determined those concerns were satisfactorily addressed and the bridge opened to bike and foot traffic in 2007.

The Southwest Journal's Dylan Thomas offered up the following tweet in response to the video:
Without further ado, here it is:


We're no engineers, but it's hard to imagine bridge designers intended for it to allow for this much vibration.

Sign of impending failure or not, it certainly isn't reassuring to watch a bridge play "The Wind Cries Mary" while you're standing on top of it.

Related:
-- Balky Sabo bridge consultant same firm that consulted on I-35W bridge before it collapsed

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12 comments
OhNoes
OhNoes

The Oresund Bridge suffers chronically from this since it crosses a water body and they've had to re-engineer dampeners because initial testing did not take into account how ice on cables magnified the oscillation.

Engineer
Engineer

I am a bridge engineer, that type of vibration causes steel fatigue at the connection, which is likely why it failed.  Same reason a paperclip breaks when you fold it back and forth a few times.

Pickler
Pickler

more info on the dog in the video please

ludwigtr
ludwigtr

You're right, You're obviously Not engineers.  The plates failed anyway, not the cable itself, the cable can vibrate all it wants so long as the plate can hold.

Albatross
Albatross

From an engineering point of view there's nothing intrinsically wrong with vibration. It can be a good way to release energy that could otherwise go into tension or torque or other physical manifestations.  Tall skyscrapers sway in the wind as part of their design, another form of vibration.

The architecture of the Sabo bridge is not radical - the Erasmus Bridge (wiki it) in Stockholm is much larger and of similar design.

One big, obvious failure in this case was the inexplicable insistence of the city of Minneapolis to continue working with the UBS inspection firm AFTER that firm failed to detect the collapse of the 35W bridge. This makes as much sense to me as Rush Limbaugh phoning Sarah Fluke for a date. This firm's incompetence has been proven in court to the tune of over $50 million dollars - are there NO other bridge inspection firms in the world? What the hell, people?

My suspicion is not design but materials. It will not surprise me in the least if the concrete or the metal of the bolts and plates turns out to be substandard. Relaxed regulation and overseas outsourcing means that a LOT of dodgy materials are being incorporated into contemporary construction. Chalk up another win for over thirty years of Republican led deregulation fetishism.

At least nobody got killed this time.

Dylan Thomas
Dylan Thomas

Yo, Aaron,

An earlier tweet gave credit to Street.mn, whose tweet brought my attention to the video. It was included in a 2/28 post on their site by the irrepressible Alex Bauman: http://bit.ly/yayI1U

HotLunch
HotLunch

Everything makes sense except "deregulation fetishism". The gov is bigger and more pervasive than ever. Step out to step up.

Lando385
Lando385

"I only watch Fox because everyone else lies". I suggest you watch the documentary "Outfoxed". It's on YouTube. It talks about how FoxNews came to be and how biased they truly are. All FoxNews does is LIE. Period. If you can't see that or use it as your only news source, then you sir are a blind, ignorant, moron. I suggest you educate yourself. Don't stay brainwashed. Time to think for yourself Hot Lunch.....

Same old story.
Same old story.

 Um, government jobs have shrunk since W. How is the government bigger? Please try to get your news from anywhere other than Fox. You'll be better for it.

HotLunch
HotLunch

I only watch Fox, sorry. Everyone else lies.

Isaac Anthony
Isaac Anthony

 Ignorant people don't let facts get in the way...

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