Closing Bell: Manhattan Bridge Shakes Its Booty
One of our daily reads is a blog called Kottke. Yesterday this Youtube of an undulating Manhattan Bridge was posted on the site. This is what bridges are supposed to do, but it’s still a little freaky to see it happening.
One of our daily reads is a blog called Kottke. Yesterday this Youtube of an undulating Manhattan Bridge was posted on the site. This is what bridges are supposed to do, but it’s still a little freaky to see it happening.
This is not vibration. This is genuine displacement of parts of the bridge due to heavy loads. The load in this case is the passing of trains that is clearly visible.
The question is: has the bridge been designed for this kind of stress? If it has, there is still the issue of material fatigue after a period of time.
Nothing lasts forever, and neither will this bridge under this kind of load.
The Manhattan bridge is anything but sturdy (relatively speaking). It has required more work than any other NYC area bridge over the years, yet the designers claimed the opposite would be true. The whole train cars on the outside bit alone was a known problem even shortly after it was built as it causes too much vibration. History Channel had an excellent shoe on the bridges of NYC and the history of this bridge sounded pretty shoddy as multiple major restoration and strengthening campaigns have been undertaken. The Brooklyn Bridge has needed far fewer.
It moves like a very sturdy bridge should.
The bridges also get significantly longer and shorter during temperature changes especially in the summer on very hot days.
OK- I am NEVER EVER going on a suspension bridge ever again! 🙂
Ok, the video Benson posted is far more disturbing. Yikes. I didn’t understand all the technical language being used in that video, but I sure as hell got the point from the images.
Worth noting that the Manhattan Bridge was designed by the very same guy that did the Tacoma Narrows. And until the major renovation project of the last few years, it too torqued, whenever subway trains ran over it – because unlike other subway-carrying bridges in NYC, the trains on the Manhattan ride on the outer edges.
Mr. B.,
Don’t worry, this happens with all suspension bridges. When one is designing a bridge, one must make sure that the vibration induced by the wind and traffic does not result in resonant vibration. Otherwise, this happens:
http://www.youtube.com/watch?v=3mclp9QmCGs
This film is always shown in engineering vibration classes, to demonstrate what happens when one does NOT consider resonance.
I wish I was on the bridge then.
If you walk the George Washington Bridge (and I recommend it), you stand there and can feel it, any day.