30% of apartments with base isolation systems suffered damage in earthquake

A survey by the Japan Society of Seismic Isolation found that 30% of buildings constructed with base isolation (menshin) systems suffered damage to the building dampers during the March 11 Tohoku earthquake.

The Society sent out a survey to 327 menshin buildings across Japan. While the majority reported no damage, 28% (90 properties) did report some kind of damage resulting from the dampers or moving parts not functioning properly. The majority of the buildings with damage were in greater Tokyo and Miyagi Prefecture. There was also one case reported in Osaka, which was a long way from the epicenter. The failure of the base isolation structure in some buildings is of concern to the Society.

There are a total of 2600 menshin buildings across Japan. This is the first investigation on the actual efficiency of this construction method following a major quake.

Buildings constructed after 1981 in Japan may be built to three different levels of earthquake resistance:

(1) Basic earthquake resistance (taishin)
(2) Vibration control (seishin)
(3) Base isolation (menshin)

All buildings are required to meet the basic earthquake resistance (taishin). Larger and taller buildings will more commonly use seishin or menshin. Menshin is the most expensive of all and is almost always used on buildings over 20 stories high. It is both expensive to install and expensive to maintain.

Base isolation system (right) versus an ordinary building (left)

View more about earthquake building codes here.

Source: The Asahi Shimbun, January 26, 2012.