Buildings in a High-Seismic Nation

Earthquake hazard is a major concern for the safety of buildings and for the well-being of our society. According to risk assessment studies, the possibility of large earthquakes place Tokyo, Yokohama, Osaka and Nagoya at a much higher risk of natural disaster than other large cities around the world.
Let me emphasize two issues. First, while sophisticated technology is available to mitigate seismic damage in buildings, the latest technology has not been tested in a major earthquake. In Japan, the 1995 Kobe earthquake was the last earthquake that caused strong ground motion in a densely populated area. While new technology has been developed and implemented since that time, the 2011 Tohoku earthquake caused widespread damage in areas where the ground motion was not severe. Our population has continued to concentrate in large cities, and buildings have become larger and higher. While we would like to believe that newer is better, we must recognize that the nature of earthquake hazard changes with time. Secondly, buildings are realized as a unique product. Unlike mechanical products, which are mass produced in the thousands or millions, buildings are custom designed to meet the needs of the owner and constructed as a one-time project. Our mission, as structural engineers, is to provide safe, reliable, functional buildings that meet personal, commercial, or societal expectations. Each building poses a unique new challenge to the structural engineer.

 

 
Picture - Steel building under construction

What is the Goal of Your Research?

My goal is to develop design methodologies that lead to safer, more reliable and more economical building structures. Another goal is to better understand how buildings really behave during large earthquakes. Among the classifications based on material, such as wood, masonry, reinforced concrete, steel, etc., my primary focus is in steel structures. Steel structures use industrialized material, i.e., steel, to form columns and beams and join them with bolts or welding (see photograph). Steel structures are used in a wide variety of buildings ranging from offices, factories, high rise buildings, to sports stadiums.

 

How do you Conduct your Experiments?

Methods of research in structural engineering include reconnaissance of post-earthquake damage, laboratory testing of specimens representing a part of a building or, on rare occasions, an entire building, structural analysis using a computer, developing theories that explain a phenomenon observed in the field or in the laboratory, and implementing research findings into design methodology. My research emphasizes laboratory testing ranging from (1) material tests, (2) component tests on components extracted from a building, to (3) tests of an entire building. The figure illustrates the concept of experiments. The scale of specimens varies from 50-cm long steel coupons, a 3-m long component, to a 20-m tall building. Our research is based primarily in (1) and (2). The example of (3), shown in the figure, was conducted at a large facility managed by a national research organization. In this particular project, conducted in 2011, a five-story building weighing five hundred tons was subjected to a ground motion recorded during the 1995 Kobe earthquake. Large tests such as this one require collaboration with many researchers and students. In our research group, we use data obtained from laboratory tests to investigate the causes of observed damage, predict possible damage in future earthquakes, and develop design methods that mitigate damage. We recognize the limitations in what we can learn from laboratory tests. Experiments are a reproduction of how a particular building, or a component of a particular building, behaves under a certain condition. Furthermore, it is not realistic to test a Tokyo Sky Tree or Sapporo Dome in full scale. We rely on computer methods to compliment what we cannot learn from experiments alone.

 

What Future do you see in your Field?

As our society continues to evolve, we will inevitably pursue more comfort, convenience, and sophistication in our living environment, and as a consequence, pursue buildings and architecture that meet those desires. More functional, more complex and larger buildings shall present new problems in structural engineering. I believe that structural engineering will continue to play an essential role in advancing our society and quality of life.

Concept of laboratory tests