An Inconvenient Truth of TAISHIN, SEISHIN and MENSHIN

In many sites, difference and feature of TAISHIN (earthquake resistant), SEISHIN (vibration control) and MENSHIN (seismic isolation) are introduced. In the brochures of condominium, technical terms like “damper” or “laminated rubber bearing” are printed. Each housing manufactures are developing new devices which can reduce building vibration.

□■□ Question ■□■

After all, which kinds of structure is the most strong for earthquake. There are too much information to judge correctly.

□■□ Answer ■□■

Base isolation is. It is clear that base isolation is the best structure for earthquake. Next is vibration control, but it is fact that there are a lot of earthquake resistant building which are better than vibration control. It is more important that “to understand what kind of performance the building designed to be satisfied” than “what kinds of structure the building adopted”.

The simplest explanation of TAISHIN, SEISHIN and MENSHIN

First, let’s explain the term easily. You can find a lot of information by internet, so here is only simple introduction.

TAISHIN: The building made stiff and strong to withstand earthquake

SEISHIN: The building installed damper which absorb energy of vibration

MENSHIN: The building with isolation layer which shut out the shaking of earthquake

Generally, relation of each performance and cost is TAISHIN < SEISHN < MENSHIN.

You know the “quality” of merits and demerits?

There is no such a technology which has “merits only”. TAISHIN, SEISHIN and MENSHIN have merits and demerits respectively. You can also find such information immediately on internet. But it is difficult to come to conclusion rightly from that information. Because it is not a problem of “quantity” of merits and demerits, but a problem of “quality”. To determine the quality is difficult for normal people.

Well studied housing sales man can tell “how TAISHIN is superior to SEISHIN or MENSHIN”, and on the contrary he can also tell “how SEISHIN is superior to TAISHIN or MENSHIN”. First-class architect may be convinced if he doesn’t specialize in structure. It is easier, in the case of normal people.

Collecting information through internet is important, but you should confirm the points.

Compare the minimum spec

I It is possible to achieve a high performance “it likely won’t break”, if you spend a lot of money for safety regardless of TAISHIN, SEISHIN or MENSHIN. In the aspect of “not collapse”, the maximum spec that each building can achieve is almost same. So you should not compare maximum spec, but minimum spec.

In fact the minimum specs for TAISHIN and SEISHIN required by Japanese building code are same. TAISHIN building designed with appropriate margin for the code is stronger than SEISHIN building designed with few margin for the code.

As an extreme example, let's assume that there is a high-rise building designed with earthquake resistant. Then a damper is being installed into that building. There are few changes regarding safety because damper is too small for that big building. It might be almost 0. But that building changes SEISHIN from TAISHIN. There is no numerical regulation about SEISHIN so that only having dampers is necessary to be SEISHIN.

Then, how about MENSHIN? In the case of MENSHIN, there is no such a handy way only adding one damper. It is necessary to add new layer called isolation layer, and it isolate building into upper part and lower part. At this point, safety of the building becomes dramatically high. as a result minimum spec of MENSHIN becomes very high.

Verification on Tohoku earthquake

No Japanese forget huge earthquake on 3/11/2011. Damage of TSUNAMI exceeded predicts. It is said that damage of earthquake was not so big, but it gave us a lot of new information about seismic safety of high-rise building. It was the first time the high-rise buildings built in cosmopolitan area were shaken strongly for a long time.

Vibration data was recorded at various buildings. Among the data of high-rise buildings, we got the result below by comparing 3 structures, TAISHIN, SEISHIN and MENSHIN.

TAISHIN ≒ SEISHIN ≫ MENSHIN

MENSHIN buildings were able to perform very well as originally predicted. On the contrary SEISHIN buildings performed like TAISHIN buildings. In short, there were few differences between vibration of SEISHIN and that of TAISHIN.

What I want to insist here is not “SEISHIN is meaningless”. SEISHIN buildings designed appropriate can reduce building vibration under earthquake very much. The SEISHIN buildings where vibration data was recorded may be designed aiming “performing very well against earthquake which is bigger than Tohoku earthquake”.

“What performance the buildings are designed to achieve” is more important than “what kind of structure was adopted”.