The series of earthquakes which hit the area in and around Kumamoto Prefecture in April 2016 are still fresh in our memory. Recorded twice at a seismic intensity of 7 , the shocks killed or injured more than 2,000 people. These casualties, for the most part, were attributed to collapsed buildings, as was the case in the Great Hanshin-Awaji Earthquake in 1995. In spite of the scale of the destruction, effective countermeasures have still to be sufficiently implemented. To avoid such tragedies from happening again, Professor Taiki Saito has been conducting research to visualize how earthquakes shake and damage buildings and hopes to apply his research outcomes to disaster prevention.
Interview and report by Madoka Tainaka
According to the Cabinet Office’s report of November 14, 2016, the earthquakes that hit Kumamoto Prefecture severely damaged over 180,000 houses, of which over 8,000 were completely destroyed . The Kumamoto eathquakes were far from being a rare occurrence. In the following year a series of destructive quakes struck around the world, such as in Italy and New Zealand, as well as closer to home, in the central part of Tottori Prefecture in October. In all of these examples earthquake-induced building collapse had a destructive impact on life and property.. Given this critical situation, the critical importance of Professor Saito’s efforts to make buildings safer by preemptively visualizing earthquake damage becomes clear.
One of the innovative accomplishments of his research is STructural Earthquake Response Analysis 3D: STERA_3D, a software tool which allows for a seismic analysis of buildings with various structures, including reinforced concrete. Professor Saito explained the aim of this software development as follows: “If you can understand in what way your house is likely to sway and collapse in the event of an earthquake, you will be better able to prepare for it beforehand. In reality, however, it is difficult to make such predictions unless you are a structural expert. That’s why we have developed a software application that, by simply entering data such as column or beam size taken from the building’s blueprints, allows you to see an animated simulation of earthquake tremors and structural vulnerability.”
The Japanese and English versions of this software are available to download for free from Professor Saito’s laboratory website. Another software tool called STructural Earthquake Response Analysis FEM: STERA_FEM, a software for visualizing the stress placed on a building’s planar structural members such as walls, is also available from the same website. Professor Saito says these tools allow you to intuitively understand the risk factors of a building by showing damage-prone spots in red. They are already in use in a wide variety of environments, including research and education.
We cannot exactly tell when or where an earthquake will strike. Toyohashi City, the home of Toyohashi University of Technology, situated above the Nankai Trough, is estimated to have a 70% chance of experiencing an earthquake of magnitude 6 to 7 on the seismic intensity scale within the next 30 years. A sense of alarm about the impending earthquake has motivated Professor Saito to work on his research.
“One of the most crucial issues in times of disaster is securing the use of disaster management facilities such as city halls, hospitals and fire stations. However, various disaster management facilities, such as Uto City Hall, were themselves damaged by the earthquakes in Kumamoto Prefecture. This factor significantly hindered the city’s evacuation and recovery operations. The problem is that you cannot tell the risk of collapse just by looking at the building from the outside,” says Professor Saito.
He further explains that a major vertical crack, for example, between two buildings of an apartment complex might appear to be hazardous to the untrained eye, but it is fairly safe as the two buildings are structurally separate. On the contrary, he adds, cross-shaped or horizontal cracks in a column are far greater hazards even when no major damage is apparent.
“To address this issue, we ran seismic simulations on the east and the west buildings of Toyohashi City Hall using my analysis tools with the data of the ground motion waveform prediction for the Nankai Trough earthquake provided by the Ministry of Land, Infrastructure, Transport and Tourism. As a result, we have found that the buildings have sufficient earthquake resistance. It turned out, however, that the west building is at risk of damage such as cracked walls and collapsed ceiling panels. Over in the east building, it was determined that in the case of a strong magnitude 7 quake, people would be unable to stay on their feet, and cabinets not secured to the floors or walls would fall over.
We don’t know for certain what would really happen since the results are only simulations based on the drawings. We might be repeatedly hit by earthquakes of an unexpected scale, just as the people in Kumamoto have recently experienced. Currently we are in the initial stages of monitoring buildings to assess whether it is safe to continue using the buildings in the event of actual earthquakes,” says Professor Saito.
More specifically, his concept involves the following. His research team installed three IT strong-motion seismometers in the city hall to continuously monitor vibrations. Every five minutes, the vibration data obtained by the seismometers are sent to the computers in Toyohashi University of Technology via the Internet for the analysis tools to run simulations in the cloud.
“If an earthquake strikes, we hope to be able to use the results of the simulations to assess whether it is safe to continue using the buildings. We are planning to implement more measures against earthquakes, such as having additional monitoring locations including fire stations and evacuation facilities, and installing a dedicated line for disaster prevention. Accumulating real-time data in the cloud can also improve the accuracy of the simulations.”
Professor Saito has also developed software that shows an animated simulation of earthquake damage inside houses such as that caused by falling furniture. This software application works on smartphones and makes it easy to run simulations, with a flexibly adjustable furniture layout and an easily configurable restitution coefficient and friction coefficient . The existence of such a tool greatly contributes to raising awareness of disaster prevention not only among researchers and experts, but also the general public.
Dr. Taiki Saito received a PhD. degree in engineering from Tohoku University, Sendai, Japan, in 1990.
Since receiving his PhD, he has been engaged in earthquake disaster engineering research as a research associate in Tohoku University, a senior research engineer in the Department of Structural Engineering of the Ministry of Construction’s Building Research Institute, and a Chief Research Engineer in the International Institute of Seismology and Earthquake Engineering, Building Research Institute. Since 2012, he has been a member of the Faculty of Engineering, Toyohashi University of Technology. He is currently working as a professor in the Department of Architecture and Civil Engineering and a director in the Research Center for Collaborative Area Risk Management (CARM) in Toyohashi University of Technology.
Madoka Tainaka is a freelance editor, writer and interpreter. She graduated in Law from Chuo University, Japan. She served as a chief editor of “Nature Interface” magazine, a committee for the promotion of Information and Science Technology at MEXT (Ministry of Education, Culture, Sports, Science and Technology).