We had a medium earthquake a few weeks
Ago but it felt pretty strong. I was at work and someone sent out an email that said “the earthquake felt stronger here because the building is on rollers” but everywhere I look the building is connected to the ground and there is a center courtyard inside our triangle shaped building that looks like a mound of earth. How can my building be on rollers?
In: Engineering
I’ve studied this a bit when I was in engineering school. I’d provide three important answers to your question.
First off – there is a relationship between the *type* of Earthquake and the *height* of the building that’s based on resonance – like the idea that a force accumulates over time. If you imagine each Earthquake as ‘humming a unique note’, certain buildings are uniquely sensitive to that specific note and other’s less so. So in your example, small buildings might all have collapsed to rubble but the sky scrapers barely swayed at all, or vice versa.
Secondly – I’m not familiar with the latest in tech but a lot of buildings in seismic areas are built where the structural backbone attaches to the ground with connections that can move. Either literally on a form of roller or a sort of rubber tube like a pencil eraser. It’s not that the whole building is rolly or wiggley, but the really important connections that are sensitive to ‘snapping’ in an Earthquake are given some flex.
Finally – many super tall buildings have something called a TMD – a “tuned mass damper” which you imagine as being an absolutely massive boulder housed up at the top of the building. If we go back to our music example, if you imagine an earthquake as plucking a guitar string and the shape of the building being the resonant body of the guitar, it’s bad news when you strum a perfect making the body vibrate along with the note, that equals bye bye building. You can thing of a TMD as a device that no matter what, “randomizes” the guitar body so that never responds to any guitar note or string you can pluck.
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