Failure of the Tacoma Narrows Bridge

• Rasine
In summary, the collapse of the Tacoma Narrows bridge was caused by torsional flutter, which is essentially aerodynamic resonance. The winds created vortices with the same natural frequency as the bridge, causing it to oscillate with a large amplitude. This was further complicated by the torsional motion and aerodynamic forces. The situation is similar to resonance caused by marching in step on a footbridge, which led to the collapse of one of the telephone poles. Recent examinations have shown that the collapse was not solely due to resonance, but also other factors. Information and discussions about the event can be found on various websites and resources.
Rasine
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?

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.

Last edited by a moderator:
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!

1. What caused the failure of the Tacoma Narrows Bridge?

The failure of the Tacoma Narrows Bridge was caused by a phenomenon known as "aeroelastic flutter," which occurs when wind forces cause a structure to vibrate at its natural frequency.

2. Was the design of the Tacoma Narrows Bridge flawed?

The design of the Tacoma Narrows Bridge was not flawed in terms of engineering principles. However, the original design did not take into account the potential for aeroelastic flutter, which ultimately led to its failure.

3. Could the failure of the Tacoma Narrows Bridge have been prevented?

In hindsight, the failure of the Tacoma Narrows Bridge could have been prevented by conducting more thorough wind tunnel testing or by incorporating additional structural supports. However, at the time of construction, aeroelastic flutter was not well understood and therefore was not considered a potential issue.

4. How did the failure of the Tacoma Narrows Bridge impact future bridge designs?

The failure of the Tacoma Narrows Bridge brought attention to the phenomenon of aeroelastic flutter and prompted engineers to incorporate more rigorous wind testing and structural supports into bridge designs. This has led to safer and more stable bridge structures.

5. Are there any lessons to be learned from the failure of the Tacoma Narrows Bridge?

The failure of the Tacoma Narrows Bridge serves as a reminder of the importance of considering all potential factors, even those that may seem unlikely or insignificant, in the design and construction of structures. It also highlights the need for ongoing research and development in the field of engineering to prevent similar failures in the future.

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