When was it first discovered that when a group of people all walked together (synchornised) that the bridge could collapse due to resonance?

I have a feeling that it was during the Roman times, but I would like reassurance.

Thankyou
Travis

In the popular US show Mythbusters, episode 12 they "busted" the myth you are asking about.

The outcome of the investigation was it is not possible to collapse a bridge by walking in step.

NC

It is fairly easy to let a string vibrate without striking it: a string will start vibrating as soon as you hit another nearby string that has been tuned to the same frequency. This phenomenon is called resonance and it not only occurs at music instruments. For instance, a company of soldiers can bring a bridge in a destructive vibration if the soldiers cross the bridge, marching in phase with each other and the frequency with which they put down their feet fits an eigenfrequency of the bridge. - University of Utrect, Department of Mathematics

As a troop of soldiers walk across a bridge, their movement causes the bridge to vibrate. If the soldiers are in step and if the frequency of their step is the same as the natural vibration of the bridge, the bridge could collapse. This is because each step that the troop makes in unison will cause the amplitude (size) of the bridge's vibrations to become higher and higher. If the amplitude of the vibrations becomes high enough, the bridge can collapse. To prevent this, soldiers purposely march out of step when crossing a bridge.

If you have ever pumped your legs on a swing to make yourself swing higher, you have observed the use of a small force to cause a large movement. Pumping a swing and walking in step across a bridge are examples of sympathetic vibration, or resonance. - Discovery.com, Education

Many examples of resonance exist, such as the shattering of a wine glass by sound, the use of a microwave oven to drive electrons in water molecules at their natural frequencies, the use of a tuned electrical circuit to filter electromagnetic waves detected in a radio receiver, and the bridge collapses that have occurred when marching troops failed to break cadence. - Lorenzo J. Curtis, Department of Physics and Astronomy, University of Toledo

I don't doubt that the Mythbusters experiment failed. There must be enough marchers and the resonance must reach a certain frequency (one that "fits" that particular bridge). But the above links indicate that it can and has happened. A continuing reference was to a bridge in the UK in 1831 that fell due to marching soldiers.

I hope Methos will add to this thread.

I'm not saying it's necessarily true, but mythbusters is, in my opinion, junk. I didn't see that episode, but nearly every one I have seen has had at least one serious methodological flaw.

The Millenium Bridge, which swayed uncontrollably due to pedestrians unintentionally walking in step, is certainly good evidence that such a thing is possible with some bridge designs, but that bridge was not typical. I don't know for sure how a typical bridge would react.

The Mythbusters team failed to collapse one particular bridge. They didn't prove it impossible.

Village Voice, while covering a story about the Brooklyn Bridge, included this historical fact:

quote:

In 1850, the Angers suspension bridge collapsed over the Maine River in Angers, France, as 478 French soldiers marched in step across it, killing 226. Though a storm raged at the time of the accident, experts blame the soldiers' marching for causing one of the anchoring cables, embedded in concrete, to tear loose.

A website called Bridgemeister also notes that the Angers bridge:

quote:

Collapsed under weight of maching troops, April 16, 1850, killing more than 200 soldiers. Collapse precipitated French virtual moratorium on suspension bridge building bringing to a close the prolific era of French wire cable suspension bridges.

However this is the only reference I could find for a bridge collapsing by soldiers marching in step. Don't know about earlier times.

In 1831 cavalry troops were marching in step across a suspension bridge near Manchester, England, when the bridge collapsed. When troopers march in cadence across a bridge, the marching may match a natural resonance frequency of the bridge. Although only a small amount of energy is added with each step, because of the resonance effect this energy will be stored. As a result, the bridge will cumulatively absorb energy from the marching men, increasing the oscillation amplitude in the bridge (just as pushing someone on a swing, in cadence, increase the amplitude of the swing). Enough energy may be added this way to damage or destroy the bridge. In fact, a concrete suspension bridge, the Tacoma Narrows Bridge, was destroyed by resonance vibrations set up by winds acting on the bridge. Today's bridges are constructed to prevent or minimize this type of wind resonance effects. - UW-Stout Physics Department

In 1831 cavalry troops were marching in step across the Broughton Bridge near Manchester England, when the bridge collapsed. Since then, marching soldiers have been ordered to break step (not to march in cadence) when crossing bridges. Marching in step to one of the natural frequencies of vibration of a bridge can cause the bridge to absorb energy cumulatively from marching troops, resulting in bridge damage or destruction. For a quantitative discussion of resonance in bridge collapse, see http://www.riverdeep.net/current/2000/08/082900t_bridge.jhtml. - High School Mathematics-Physics SMILE Meeting
1997-2006 Academic Years
Mechanics: Resonance

In 1831 troops crossing a suspension bridge near Manchester, England, supposedly marched in time to the bridge's sway. Boy, did they get a surprise. - The Straight Dope

I Googled "resonance + bridge + marching + 1831" and got this result.

On review I see that the passages I quoted earlier don't actually implicate harmonic resonance -- rather than dead weight -- as the culprit in the Angers bridge collapse. Still, the Mythbusters experiment adds nothing to settle the question of whether it has ever occurred. Can a bridge deck have an f₀ of around one second to match a typical marching rhythm?

The bridge must have been rebuilt have found a reference for 1906

quote:

The following from the Manch. City News of 20 Jan. 1906 gives a pleasant picture of Broughton as the correspondent saw it seventy years ago: 'At the Strangeways end of Broughton Lane were a few residences, whilst in the near fields was a nest of working men's lock-up gardens, wherein many a rare pink and picotee, and many a swelling stock of celery were nourished with fond and jealous care. The lane was knee-deep in sand, and the resort of numerous red and brown butterflies, till it joined the lower road from Broughton Bridge near the suspension bridge. So by a few cottages to the Griffin Inn, the Cheetham Arms, and its opposite ford —a noted bathing-place for Manchester youths.

From: 'Townships: Broughton', A History of the County of Lancashire: Volume 4 (1911), pp. 217-22. URL: http://www.british-history.ac.uk/report.asp?compid=41408. Date accessed: 02 August 2006.

I didn't add the Last part (neat trick )
Ps There is reference to a ford (same location)
Recent maps show nothing at that location unless there is a footbridge or weir at the rough location? (highest resolution aerial photo) Nothing noted on Map or my A to Z street Map book of Manchester

Look just above East Philip Street(North west of the red circle on the river)


There were recent issues to New bridges of similar construction in London & Newcastle and I think Dublin (Ireland) the London Bridge had to be braced to Damp the Harmonics

Resonant vibrations are considered in bridge design and it is very unlikely that any combination of human vibrations (considered live loads) would create a resonance that would bring down a bridge unless there were additional influences at work - high wind loads, earthquake, soil erosion, breakdown of materials, etc. and even then, unlikely.

The Tacoma Narrows bridge collapse and other examples of bridge failure are a sophomore level subject in structural engineering/architecture. It is not an obscure consideration.

Most small bridge projects are extremely overdesigned and most large bridge projects are highly engineered and of course this would be taken into consideration by well educated experts. Mythbusters failed because the live load design of bridges or any large structure will more than compensate for live load conditions.

In addition most existing bridges have been so well studied and examined that harmonic breaks have been installed if there was a need.

Definitely just a myth.

I'll stick with what the various mathematics and physics people say, that it is a factor that must be considered. The fact that "Resonant vibrations are considered in bridge design" certainly seems to imply that, at one point in time, it wasn't considered.

The original question was " When was it first discovered that when a group of people all walked together (synchornised) that the bridge could collapse due to resonance?

My guess is somewhere in between the 1831 collapse of the suspension bridge near Manchester, England (as noted by the University of Wisconsin-Stout Physics Department) and Aminator's sophomore year in college.

Thanks, Ami. Do you know about older bridges?

methos:

Older bridges were built with great mass and would not resonate like a suspension bridge. Wood bridges would have been susceptible but I believe the real problem came about with the development of lighter structural systems like steel and prestressed concrete. So, my answer to the original question is that this understanding of resonance would have started with the technology of steel and concrete bridges starting in the early 1800's.

My point in my first answer, which IMO the "site admin" has been rather rude about, was that any Mythbusters episode which attempts to prove that marching resonance could have brought down a bridge doesn't take into consideration that bridges have been altered to make them safe as our understanding of engineering increases. This is the case with seismic conditions and is certainly the case with resonance and is now going to be the case with the use of epoxy anchoring. The Millennium bridge is a good example. Initial design was inadequate for the actual live load and tuned mass dampers had to be added. This bridge actually illustrates the lightness of steel construction as it relates to resonance quite well. It's a very narrow little bridge with a very long span. It was apparently really swaying before it was closed and altered.

This is the same with high rise buildings. The more massive a building is the less it's going to sway. In some buildings, rarely, with slender profiles a tuned mass damper is placed at the top to counter this effect. In most buildings the slenderness ratio is considered very carefully not only for safety but also because occupants will get motion sick. I know a bit more about this than I know about bridges and can say that older buildings would not sway due to their mass so the engineering principles developed along with the technology over the course of the past 150 years... not all at once by any means.