How did you become involved in your current research?

Fig. 1 Seismically isolated structure


Photo 1: The National Museum of Western Arts (Ueno, Tokyo), which has been retrofitted using seismic isolation.

Japan is one of the most earthquake-prone countries in the world, and so we must always take earthquakes into account when designing building structures. This is known as “seismic design”. One of the newest earthquake-proofing techniques is known as seismic isolation. Seismic isolation is an innovative technology, involving the installation of special devices (seismic isolation devices) undernearh a building to decouple it from earthquake ground motion (Fig. 1). After I graduated university I went to work for a construction company and was immediately put in charge of a seismic isolation technology development project. As I worked on the project, I started to think that if we could roll out this sophistcated technology further throughout the world, we could liberate people from the fear of earthquakes. At the time, however, seismic isolation system was an expensive, specialized method of construction. I began research, therefore, into how we could develop a cheaper, high-performance version of seismic isolation, that could be more widely used in society.

 

How does this affect our day-to-day lives?

Seismic isolation is capable of reducing vibrations inside a building during an earthquake to 1/5 its original intensity. As such, it not only prevents damage to the building itself, but protects items stored in the building from falling over or dropping to the floor. For example, if medical equipment in a hospital is damaged in an earthquake, then medical treatment may have to be stopped, even if the building itself is not damaged, but this can be prevented if the building is seismically isolated. In a major earthquake, the costs due to damage can quickly challenge a country’s budget. The use of seismic isolation increases the cost of construction by a few percent, but this small investment in the future can be expected to minimize the cost of damage in the case of an earthquake.

Seismic isolation can be used not only for new buildings, but also as seismic retrofit for existing buildings. Seismic isolation devices have to be installed underneath a building, so they are not visible to people under normal circumstances. This makes it suitable for retrofitting buildings whose design cannot be changed. Seismic retrofit of historic buildings, such as important cultural heritages, is one of the things seismic isolation is best for (Photo 1). Furthermore, since we do the retrofitting work underground, the building can be used even when the construction is ongoing. The work is done before anyone realizes it. Cultural heritages retrofitted using seismic isolation will no longer shake during earthquakes, and so should outlive all of us as a result.

 

How do you go about your research?

 Since buildings are extremely heavy, the seismic isolation devices that are used to support them are enormous. One type of seismic isolation devices is a multilayered laminated rubber bearing (Photo 2). The multilayered laminated rubber bearing is made up of alternate layers of rubber and steel sheets, so that while bearing the weight of the building they can also deform in a horizontal direction, by tens of centimeters. We need to use a massive test device in order to confirm its performance. Ordinarily, we would use a device at the factory that manufactures the laminated rubber bearings (Photo 3). When a major earthquake occurs, the earth’s surface can move at speeds of up to 1 m per second. It is not currently possible to implement experiments on laminated rubber bearings that can replicate a major earthquake within Japan, so we are performing tests overseas (Photo 4).

Photo 2 Laminated rubber bearing (Photo supplied by Bridgestone) Photo 3 Testing equipment (Photo supplied by Oiles Corp.) Photo 4 Earthquake high-speed loading device (University of California at San Diego, USA)

Fig. 2 Seismic response analysis system

When designing seismic isolation system, we use a computer simulation to confirm that the vibration will be inhibited sufficiently for the building to be safe. Fig. 2 shows a seismic response analysis system, designed to predict with great accuracy the way in which buildings will shake. Many seismically isolated buildings have now been designed using this analysis system. The seismic isolation for the National Museum of Western Arts, which I introduced above (Photo 1), was designed using this system.

 

What are you aiming for next?

There are other ways of controlling vibration in a building, one of which is the technology known as energy dissipation and active control. Energy dissipation involves converting the vibrations from an earthquake that enter a building into thermal energy using a device known as a damper, which releases the energy into the air. Compared with seismic isolation, which is suitable for low buildings, energy dissipation is suitable for tall buildings such as skyscrapers. Tall buildings also vibrate in strong winds, such as those generated by typhoons. We use active control to suppress this. Active control involves placing a huge pendulum on the top floor of the building, which cancels out the shaking. We can also improve performance by using a sensor to detect vibration in the building and control the movement of the pendulum with computers. Altogether, seismic isolation, energy dissipation, and active control are referred to as vibration control technologies.

I am aiming to create the ultimate safety in building structures, which cannot be damaged by earthquakes or typhoons because they do not shake. Through a combination of vibration control technologies, we can create buildings whose residents do not even realize that an earthquake or typhoon has struck