On entering London's Albert Bridge over the Thames between Chelsea and Battersea there is a sign which reads "All troops must break step when marching over this bridge." Please, what does this mean?

MonkeyOnALeash

To break step means to stop a uniform cadence. The myth behind this need is the prevention of a harmonic disturbance that would cause the bridge to collapse due to the rhythmic marching of a multitude of Soldiers. It would require a whole Countries forces marching in unison for a looong period of time across a weak bridge for this collapse to happen! Jul 29 07, 2:51 PM

queproblema

This site claims it's true. "A company of soldiers marching in step across a bridge may in this manner cause the bridge to collapse even though the bridge would have been strong enough to carry many more soldiers had they marched out of step. For this reason soldiers [are] required to "break step" [when] crossing a bridge." http://72.14.253.104/search?q=cache:1zGp1rEiV9cJ:www.projectintermath.org/docs/wingresonance.pdf+www.projectintermath.org/docs/wingresonance&hl=en&ct=clnk&cd=1&gl=us Also see "Galloping Gertie" under "Tacoma-Narrows Bridge" in Wikipedia for an oft-cited but erroneous example of this; the bridge collapsed due to wind, not marching. Jul 29 07, 8:20 PM

bloomsby

I used to live close to the Albert Bridge in London and the notice was indeed there, signed by Reginald Mackenna, First Lord of the Admiralty (presumably standing in for another minister), and had a date from 1911. This has in the meantime been replaced by a more modern notice. The original Albert Bridge was a weak suspension bridge. Heavy vehicles, such a buses, were not allowed to use it. However, it was strengthened in the 1970s by addition of supports. The danger posed to a weak suspension bridge by troops marching in step is that it will oscillate, swaying from side to side till it breaks loose. Here's a link on the problem of oscillating bridges: http://www.brantacan.co.uk/oscillation.htm Jul 30 07, 3:58 PM