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Q & A: Earthquake and building frequencies?

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Most recent answer: 02/23/2010
Q:
Someone asked "What happens if the natural frequency of a building matched the frequency of an earthquake?" so I'm curious to know how do people (I guess engineer) know the frequency of a building, and whether changes can be made to the building to change its period?
- Diane King (age 17)
Pompano Beach, Florida, Us
A:
This is an important consideration in the design of modern buildings.  As you have guessed, when the dominant frequency of seismic waves is the same as the natural vibrational frequency of a building structure... watch out.  When the resonance frequency is matched the resulting buildup of the oscillations puts enormous stresses on the structural elements. 

I called up an architect friend of mine who specializes in structures to find out what they do  these days.   Yes, they do have computer programs that can calculate the various resonant frequencies of a building.   Yes, in order to alleviate the problem, they do design the basic structure of the building to be rather stiff; a sort of box-like structure.  In addition they install mechanisms that will counteract the seismic motion by actively moving large masses back and forth by means of computer control. In the top of most major skyscrapers there is a huge mass on the top floor that moves back and forth in order to counteract the seismic motion.  Many small buildings have soft damping mechanisms in the basement.  The building, in a sense, floats on a shock absorber. 

LeeH



(published on 02/23/2010)

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