Failure of the Tacoma Narrows Bridge

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    Bridge Failure
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Discussion Overview

The discussion centers on the physics behind the collapse of the Tacoma Narrows Bridge, exploring concepts such as torsional flutter, resonance, and aerodynamic forces. Participants share insights and seek clarification on the mechanisms that led to the bridge's failure.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks to understand the cause of the collapse, specifically mentioning "single-degree-of-freedom torsional flutter."
  • Another participant suggests that resonance played a significant role, noting that wind created vortices matching the bridge's natural frequency, leading to large amplitude oscillations.
  • A participant describes "torsional flutter" as a form of aerodynamic resonance, comparing it to a fluttering piece of paper and sharing a related anecdote from their training.
  • Some participants indicate that recent examinations suggest the situation is more complex than just resonance, with one promising to provide further information later.
  • Another participant expresses skepticism about whether resonance alone was sufficient to cause the collapse, indicating a need for more information on the new explanations.
  • One participant mentions that the added complexity may arise from aerodynamic forces and the torsional nature of the motion, contrasting it with typical resonance scenarios.
  • A reference to a textbook discussing the Tacoma Narrows Bridge is provided, indicating that it includes a detailed analysis of the topic.
  • A link to a related thread is shared for further exploration of the topic.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as there are multiple competing views regarding the mechanisms behind the bridge's failure, particularly concerning the roles of resonance and aerodynamic forces.

Contextual Notes

Some discussions highlight the complexity of the situation, indicating that assumptions about resonance may not encompass all contributing factors to the bridge's collapse.

Rasine
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i am, thus, attempting to understand the physics of the collapse of the Tacoma Narrows.

can please explain what i have found to be the cause of the final distruction: single-degree-of-freedom torsional flutter?

or if you know anything else about this event, please explain!
 
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If i remember the problem had to do with resonance, You see the winds were making vortices with the same natural frequency of the bridge, thus making the deck of the bridge oscillate with a rather huge amplitude. Another fact is that the wind making the resonance had a speed less than what the bridge was made to handle.
 
"torsional flutter" is a way of describing, essentially, aerodynamic resonance. Its the same as when you drop a piece of paper and it flutters back and forth.

In my basic training at the Naval Academy, there was a footbridge with two telephone poles supporting the center span leading to some athletic fields. The resonant frequency was roughly the same as the double-time marching (running) pace. We had been instructed not to march in step across the bridge, but one instructor forgot, marched his squad across, and snapped one of the telephone poles. After that, they replaced the center span with steel, which being much more rigid, has a much higher resonant frequency.

edit: http://www.enm.bris.ac.uk/research/nonlinear/tacoma/tacoma.html is a good site with info, photos, and videos of the Tacoma Narrows bridge failure.
 
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More recent examinations have shown that it is a lot more complicated than simply saying "resonance"! I don't have it with me now but if I remember tomorrow I will post a link to a discussion.
 
I would like to see those new explanations, Halls. I thought the oscillation due to resonance was more than enough to cause a collapse of the Bridge's deck.
 
I'm not certain, but I think the added complexity was due to the aerodynamic forces and the fact that the motion was torsional. The situation I described is more typical of resonance: simple harmonic motion in the axis where the bridge is loaded (vertical), with a driving force that is periodic, but always the same and far too small to cause failure if it were constant.
 
I don't have web-site references but

Differential Equations by Blanchard, Devaney, and Hall has a long discussion of the Tacoma Narrows bridge and refers to
"Large-amplitude Periodic Oscillations in Suspension Bridges: Some New Connections with Non-linear Analysis" by Lazer and McKenna, SIAM review, vol. 32, no. 4, 1990, pp. 537- 578.
 
thanks to everyone for helping me understand!
 

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