Physics applied to minimize Nature’s Forces – An analysis of Tokyo’s tall buildings
March 13, 2011

Today is the 3rd day since the major earthquake hit Japan. The number of after shock tremors have gone over 260 of different categories. Till March 19th more are expected.

I stay on the 9th floor in an apartment building in central Tokyo. The tremors are very visible and you can feel them very much. The swaying of building reflects the intensity and duration of these tremors.

Earlier today I visited Kamalesh ji at his apartment and he lives on the 22nd floor of the building. As we discussed what things fell in his apartment. The answer was none. So what happened?

The answer lies in the application of physics and engineering that was used in buiding these tall apartment complexes.

Here is a brief on that:

  • An active mass damper system, containing two master dampers is installed on the topmost floor of the building.
  • All the other floors contain hysteresis and viscous dampening devices within their structures.

What it helps with?

  • The above systems allows to cope with severe swaying caused by large earthquakes (200-300 gals acceleration response spectrum of the hysteresis theory).  So, what is this “gal” is the unit of measure for acceleration in gravitational science. gal is written in lower case and it is 1 cm/(s^2) = 1 cm per second square. The unit gal is name after Galileo the famous scientist.
  • The above systems also allows for lesser swings caused by large winds (20-30 gals acceleration response spectrum).
  • The building has been constructed to withstand an earthquake of seismic intensity 7 on the Japanese scale and a maximum velocity of 50 centimeters/second.

What is the Active Mass Damper System?

  • A sensor that detects swaying is coupled to a computer.
  • It minimizes the swaying by controlling a weight installed in the uppermost part of the building.
  • It can reduce the impact of a 25 meters/second wind by 50%.

What are damping devices?

  • There are two damping devices (a) Hysteresis damper, and (b) Viscous dampers.
  • Hysteresis dampers are built based on physics theory of hysteresis
  • Viscous dampers are based on energy absorbing materials.

However, the physics and the engineering can reduce the impact of Nature’s force upto a certain degree, as the predictability of Nature’s force is still an ongoing research topic.

On the life in Tokyo, the stores have certainly run of fresh vegetables and other items mostly due to lack of transportation. The metros have finally started to work. Not sure about the fast trains. Lets see what Monday brings.