Resonance and bridge collapses
I remember the discussion of resonance from physics class a long time ago because of the illustration of the collapse of the Tacoma Narrows Bridge which was presented as a result of resonance resulting in part from the fact that the bridge's two suspended spans were the same length.
According to this site some engineers question the relevance of the resonance issue.
I noticed something interesting about the recent collapse of the I-35W bridge in Minneapolis. The west most 4 lanes were carrying traffic. The next segment of 4 lanes, of presumably equal width, were having concrete removed. Then there were another 4 lanes of traffic and the final 4 lanes were having concrete removed. The Minneapolis Star Tribune has reported that workers told a local police officer that they had noticed the bridge was wobbling and the wobble was increasing with each layer of concrete removed.
Could some type of resonance situation have occurred because of having two areas of equal width having traffic induced vibrations alternated with two equal width areas without such vibrations which were also becoming physically different? And if the bridge were close to falling apart anyway could this have reduced the bridge's stability making it more likely to fall?
Incidentally, if you think resonance is possible and have the appropriate academic credentials you might want to contact one of the news channels. You might also want to contact a trial lawyer or two about being a paid witness in one of the lawsuits that is likely to come from the collapse.
I am also curious about the degree to which the components pressing against each other might have helped keep the bridge standing. For example, the weight of the bridge might have kept the metal supports in place even though one of them may not have been actually attached to the pier upon which it was standing. The bridge fell like a house of cards and maybe that is because at the time it was held together more by physical forces than mechanical connections.
An engineer called into a talk radio program I was listening to on my way to work here in Minnesota, talking about resonance and the cumulative effects of those frequencies on the former bridge. He mentioned that a train was travelling near to the bridge at the time of the collapse, which I have not yet confirmed, but went on to talk about a similar concept of the bumper-to-bumper traffic and the collection of their vibrations along with the resonating movement of the passing train as a primary cause for the collapse. Of course it should be considered that the bridge was rated as "deficient" and affected by unrelated reconstruction of that transportation system.
I don't know.
Resonance is when you send a wave of vibration at certain frequency. Meaning eventually the waves would slowing move throughout the structure and causing it to first vibrate and then after a long enough time. The structure will violently shake until being ripped apart.
Resonance is equal throughout the entire structure or at least will be if given enough time.
The bridge was probably old and became unbalanced and finally reached it's limits.
Unless somehow there was a traffic jam on the bridge in which the cars where stuck on the bridge for a long time not moving and the shaking of all the engines combined created the perfected resonance frequency of the structure.
Who knows though.
You mean like Taucoma Narrows bridge natural frequency?
Be kind to yourself always.
I'd say they should look at the design of this bridge and the maintaniance of it also. They were working on it when it collapsed so that tells me there were already existing problems but with what I don't know. I think they will find that another problem happened, it wore out sooner that it was supposed to for it was built over 50 years ago and the loads then were far less than now.
There was a train with some of the rail cars crushed by a portion of the bridge.
Originally Posted by original
I don't recall seeing pictures of a bridge collapse with all the spans affected like this one except in one of the California earthquakes. The bridge fell like a "house of cards" as if the parts were essentially just "propped together" waiting for something to destabilize it.