4 ms·
> When people walk across a bridge and it starts to sway, they start to lock step and then resonance, where each step reinforces the last kicks in and more and
by kazen44 6y ago
> When people walk across a bridge and it starts to sway, they start to lock step and then resonance, where each step reinforces the last kicks in and more and more energy causes sway, shear and what have you forces. It gets worse and worse and then failure. Tacoma Narrows is another classic example of resonance but due to wind - that informed designs that don't fly!
this anecdote reminds me of the story of ancient rome. (I don't know if this is actual history or a myth).
Apparently, when roman military engineers build a bridge, they where forced to stand beneath it while the rest of the cohort marched across the bridge to test it's strength.
Marching gives exactly this same resonance effect.
- tjalfi 6y agoYour anecdote reminds me of this quote about Dupont's safety program. "My company has had a safety program for 150 years. The program was instituted as a result of a French law requiring an explosives manufacturer to live on the premises with his family." - Crawford Greenewalt
- nuclearnice1 6y agoApparently the British army were told to break step when crossing bridges to avoid that potential disaster. https://en.m.wikipedia.org/wiki/Broughton_Suspension_Bridge https://en.m.wikipedia.org/wiki/Broughton_Suspension_Bridge
- lou1306 6y agoI think it's common military training in a lot of places. I'm italian, my dad did his service in the Engineering corps (Genio) and he told me the same story. No lock step while crossing bridges.
- randomswede 6y agoNever had it in re bridges, but "no lock-step while carrying a stretcher" was a mandatory part for me.
- gerdesj 6y agoIt's true. My dad was a Colonel, my mum a Captain and I was a cadet! Grandad was a Major etc etc
- todd8 6y agoMy father was an officer in the Marine Corp during WW2 and he told me (many years ago) about being taught this in his training.