question in Ballast (15)



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    Michael Ermann

    Think instead of you as a child on a swing: if you pump your legs at just the right rhythm you go higher each time (but if you pump your legs at the wrong time you don’t) ….likewise with buildings, if the wind or earthquake pushes periodically at just the right rhythm small forces can eventually lead to large building sways and catastrophe. . . Buildings each have their own “natural frequency,” based on their weight and stiffness, and if the wind or seismic forces push at a similar frequency the sway will increase at each pass. See this famous video of the Tacoma narrows bridge where the frequency of the wind through the ravine twists the bride more with each sway until it collapses
    Had the bridge been stiffer the natural frequency of the bridge wouldn’t have aligned with the frequency of the wind pulsing through the ravine. The same thing almost happened to the Golden Gate Bridge so they stiffened it.-Michael Ermann, Amber Book creator

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    Arjumand Anjum

    Hi Michael, 

    Following is just a thought, doesn't make sense logically but does so on paper. 

    Tacoma narrows bridge dint have to be stiffer, it could have been more flexible. May be then, its period would have been different than frequency of the wind pulsing through the ravine? 

    With dissimilar period, the bridge would not have swayed so much?

    Kindly explain,


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