Relation with Earthquakes

week7

     Hello!
     I will tell you about relation with earthquakes.
     Since the Great East Japan Earthquake, "a house to withstand earthquakes" is more strongly demanded, and, today, construction technique such as "earthquake resistant", "active vibration control", and "seismic base isolation" is generally known well. However, few people still understand the difference among them. Then, I will tell you about it.

     A building which is called "earthquake resistant construction" is one which suffer little damage from a tremor with an intensity of 4-5 on the Japanese seven-stage seismic scale and which do not collapse when a tremor with an intensity of more than 5 on the Japanese seven-stage seismic scale occur. "Earthquake resistant construction" have tough and solid structure section to withstand earthquake and suffer seismic energy to its entire building, so it do not collapse. But there is some danger of earthquake resistant construction's suffering serious damage indoors.
     "Active vibration control construction" is a structure which is equipped with some damping device such as a damper and so on and which absorbs the energy.
     "Seismic base isolation construction" absorbs a tremor of earthquake with seismic isolation device, and controls transmission of seismic energy to the top of the building. Compared with the seismic design, "active vibration control construction" reduces the strength of shaking during a major earthquake to 1/3-1/5, so "active vibration control construction" can suffer less damage but also to not only the building but also indoor. The rental housing do not have active vibration control construction because it costs much money to build it.

     As mentioned above, each how to withstand earthquakes is different. The most popular construction in Japan is "earthquake resistant construction" and "earthquake resistant construction" is used in about one hundred thirty thousand building per year now. On the other hand, now "seismic base isolation construction" attracts attention, but the number of it is still small and about two hundred fifty building per year. For example, Tokyo Station Marunouchi Building renewed recently  also has "seismic base isolation construction". Therefore, I tell you about "seismic base isolation construction" in detail.
   
      Every three structure is excellent in terms of preventing the destruction of the building itself, but only "seismic base isolation construction" has advantage of  "reducing the shaking in the building". The mechanism in "seismic base isolation construction" is that seismic isolation devices which are embedded in the foundations absorb the violent earthquake energy, turn into a gentle roll, and minimize the damage of furniture's falling and so on. It is said  that the tremor of seismic base isolation is one-third as large as that of earthquake resistant and active vibration control. Then, I will tell you about what is "seismic isolation devices". "Seismic isolation devices" are "laminated rubber" formed iron and rubber into a thing like mille-feuille and withstand pressure of up and down by many layers of rubber and steel and deform and restore flexibly for lateral vibration.

     The reason why seismic base isolation less prevail than earthquake resistant is that construction costs are higher and construction period is longer. However, it is said that a great earthquake such as "capital epicentral earthquake" and "Tokai earthquake" occur in Japan in the near future, so you have to take precautions against earthquakes at a little cost.