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When the plate of the bridge assumes the unnatural shape showed in the below picture, what is this phenomenon called? Contortion (example: the bridge was contorting ...). I'm not so sure, as I think contortion is normally referred to the (unnatural) shape of human/animal body. Is there a better word?

enter image description here

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In case anyone's interested - the bridge shown is the Tacoma Narrows Bridge - en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940) – Colin Pickard Jun 6 '12 at 20:49
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What aspect of the phenomenon are you looking for a word to describe - the motion of the bridge? the static shape as frozen in the picture? the physical process that caused the motion? – LarsH Jun 6 '12 at 21:16
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All the word suggestions below are great answers, and are all words that describe it adequately, but I've actually heard the sentence "He pulled a Tacoma Narrows," in reference to someone twisting wildly as they fell down. It seems to be a very unique thing. – Nick Anderegg Jun 6 '12 at 22:39
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The phenomenon is caused by resonance. – ncmathsadist Jun 7 '12 at 1:34
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If you've never seen the footage of the bridge (nicknamed 'Galloping Gertie') swaying and undulating, see this video. It's impressive. – JLG Jun 7 '12 at 6:57
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12 Answers

up vote 25 down vote

There are different technical words to refer to the motion of a suspended bridge. Oscillation is the most widely used term.

For a potentially destructive oscillation, you could use flutter; this is a technical term.

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Oscillation is the result of the resonant response to wind blowing over the bridge. – Jim Jun 6 '12 at 20:30
up vote 25 down vote

While contortion may sometimes refer to the shape of a human/animal body, it does not necessarily.

Contortion and torsion both refer to the twisting (unnatural in the case of contortion) of an object, which certainly seems relevant for the photo you provided.

The phenomenon in question actually deals with the resonance of the bridge, and is not really a "twisting" motion as contortion implies, but is actually an oscillation due to resonant frequencies of the object. (Though it certainly appears as a twisting motion when driven to that type of extreme.)

As pointed out by others and in comments, aeroelastic flutter played the major roll and not resonance. Though it remains an example of resonance, calling it resonance oversimplifies what actually occurred and it would be more accurate to state that it was aeroelastic flutter combined with resonance.(source1)(source2)(source3)(source4)

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'tortuous' is the technical medical term for a vessel that has more bends in it than usual. – Mitch Jun 6 '12 at 19:47
+1 for explaining the relevance of resonance. – Mechanical snail Jun 7 '12 at 3:03
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Although the Tacoma narrows is always shown as a classic example of resonance - it wasn't. The movement was caused by flutter, it didn't have to be at a resonance. – mgb Jun 8 '12 at 15:41
@mgb Edited to reflect the roll of flutter, though resonance still played its part (the best explanation is actually a combination of the two). – NominSim Jun 8 '12 at 15:57
up vote 15 down vote

I'd say buckled, which fits the Dictionary.com definition: "3. to bend, warp, bulge, or collapse: The bridge buckled in the storm."

There may be a technical engineering term, but I suspect most people would grasp buckled more readily.

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"Collapse" is the version "buckled" that immediately pops into mind for me - it's not a good choice if you want others to easily distinguish the collapsing vs non-collapsing type of "buckling". – Izkata Jun 6 '12 at 23:15
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Buckled actually implies something short of collapsed to me. I get the picture of something with a major structural problem but that is still standing. There is room for interpretation, I agree. – Bill Lefurgy Jun 7 '12 at 0:14
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Of course, this bridge actually did collapse. – Mechanical snail Jun 7 '12 at 3:02
@Mechanicalsnail: My thoughts excactly when I was reading the definition in this answer. – awe Jun 7 '12 at 8:58
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buckling has a specific technical meaning, when a member fails under compression by folding - like a crushed drink can. If you are describing the failure of a bridge I would avoid it – mgb Jun 8 '12 at 15:38
up vote 12 down vote

The phenomenon that cause this movement is called "Resonance". The wind at a specific speed cause a Oscillation on the bridge that is equal the "Natural Frequency" of the structure.

The catastrophic vibrations that destroyed the bridge were not due to simple mechanical resonance, but to a more complicated interaction between the bridge and the winds passing through it — a phenomenon known as aeroelastic flutter.

Source: Resonance Failure of the original Tacoma Narrows Bridge

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This vibration was caused by aeroelastic fluttering. The wind speed measured that day was being fairly constant, there was no forced resonance. – user19341 Jun 7 '12 at 9:30
@ArchJ Aeroelastic fluttering and resonance oscillation go hand in hand usually. They aren't normally disjoint occurrences. – NominSim Jun 7 '12 at 16:04
When the oscillation matches to the natural frequency it intensifies the amplitude of the oscillation. Wikipedia:"In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. At these frequencies, even small periodic driving forces can produce large amplitude oscillations, because the system stores vibrational energy." With out the resonance the wind can produce this movement, but the bridge will offer a great resistence and turn back to original shape. – Vitim.us Jun 7 '12 at 18:57
up vote 12 down vote

I don't think it would be such a bad thing to fall back to a simpler word: twisted. In this case, if you were to say "in high winds, the bridge surface twisted" (or "the bridge became twisted"), I think that adequately (and clearly) communicates what we see in that photo.

I'm all about using the best word for the situation-- and in this case, to communicate that concept, I think "twisted" is optimal.

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I would use twisted if you are writing a general piece. Trying to sound better by using technical terms is confusing if you don't use them in their exact technical meaning. – mgb Jun 8 '12 at 15:40
up vote 7 down vote

The first word that came to my mind was undulate.

undulating
present participle of un·du·late (Verb)
1. Move with a smooth wavelike motion: "her body undulated to the thumping rhythm of the music".
2. Have a wavy form or outline: "delightful views over undulating countryside".

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up vote 5 down vote

You are correct that "contortion" is often used in reference to human bodies. A preferable alternative might be "contorted", which has no such connotations and can be used appropriately with reference to a physical object.

UPDATE: As NominSim points out Wikipedia disagrees with the distinction I suggested here. Nevertheless, I maintain that in common usage, "contortion" is often associated with "contortionists" - a human activity. Wikipedia's redirect notwhithstanding, contorted does not have the same association. Perhaps this is just a matter of my own opinion, however.

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Your wikipedia link is a redirect from contorted, seems unjustifiable to suggest a word that links directly to the word in question. – NominSim Jun 6 '12 at 17:56
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Contortion is a noun, contorted is an adjective, and both are derived from the same verb stem of "contort." They are essentially the same word in this case. – fluffy Jun 6 '12 at 17:58
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@fluffy: watch out for the etymological fallacy. Just because two forms have the same root, does not mean they have the same meaning, or range of usage, or connotations. – LarsH Jun 6 '12 at 21:13
@LarsH I agree, however in this case fluffy is correct, they have the same meaning. In fact contortion defaults to contorted in many online dictionarys. – NominSim Jun 7 '12 at 12:48
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@NominSim: I would agree with kmote that the two words have somewhat different (though overlapping) connotations (associations). Most dictionaries are usually far from complete when it comes to that level of nuance. – LarsH Jun 7 '12 at 15:44
up vote 5 down vote

My pick would be warp. For example, 'the bridge's warping became so extreme that it started to shake itself apart.'

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Warping is generally a gradual and permanent deformation (e.g. of a board under long-term load) rather than sudden changes like this. – Mechanical snail Jun 7 '12 at 3:04
up vote 3 down vote

This phenomenon is called resonating. Example: The bridge was resonating until the forces induced were greater than the force it could withstand, and it collapsed.

Resonance, incidentally, implies that the amplitude of oscillation will increase until either the dampening forces prevent further increase or until the forces become too great for the structure to withstand.

Or, if you're looking for the specific shape, I'd use twisting or torsioning.

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up vote 1 down vote

It isn't clear from your question whether you are looking for a simple description of the state of the bridge or a more technical answer. My feelings are that the words 'distortion' or 'distorted' are the most appropriate.

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up vote 1 down vote

I would go with bucked:

v. bucked, buck·ing, bucks v.intr.
1. To leap upward arching the back: The horse bucked in fright.
2. To charge with the head lowered; butt.
3. To make sudden jerky movements; jolt: The motor bucked and lurched before it finally ran smoothly.
4. To resist stubbornly and obstinately; balk.
5. Informal To strive with determination: bucking for a promotion.

It works both with the literal meaning (definition 3) and as metaphor (definition 1): The bridged bucked in the wind.

If the motion in question is gentler, sway seems like a good choice.

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It doesn't seem like all that sudden to me. Buckled is better. – Muhd Jun 7 '12 at 0:14
Are you suggesting that 'bucked' be used as an adjective? or are you just giving the verb as in 'The bridge is bucking' ? – Mitch Jun 7 '12 at 1:51
@Mitch The usage here is as an intransitive verb. – Izkata Jun 7 '12 at 2:49
up vote 1 down vote

From a mechanical engineer's perspective, it is correct to say that the bridge is contorting.

I would comment on some of the previous posts, but I am new to this forum.

Although not specifically asked for, many others are identifying the cause of this torsion as resonance; however, this is not technically correct. As Shyam points out, the bridge failed due to a phenomenon called aeroelastic flutter.

Resonance is a technical term which implies that a periodic force was applied at the same frequency of the structure's natural frequency. The wind blowing on the Tacoma Narrows Bridge was not periodic in nature: it was a constant breeze. Thus, resonance is not technically correct here.

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