NATIONAL SCIENCE FOUNDATION
TOKYO REGIONAL OFFICE
The National Science Foundation's (NSF) Tokyo Regional Office periodically receives and disseminates reports on research developments in Japan that are related to the Foundation's mission. It also provide occasional reports on developments in other East Asian Countries (http://www.twics.com/~nsfasia/as-reports.htm).
These reports present information for the use of NSF program officers and policy makers; they are not statements of NSF policy..
Special Scientific Report #01-06 (October 8, 2001)
RETROFITTING OF TRADITIONAL JAPANESE HOMES FOR SEISMIC ACTIVITY
The following report was prepared by Forrest James Masters, a Ph.D. candidate in the Department of Civil and Coastal Engineering at the University of Florida. Mr. Masters was a participant in the 2001 Summer Institute Program in Japan, co organized by the National Science Foundation and the Japanese Ministry of Education and Science (Monbukagakusho). He may be reached at phorrest@ufl.edu.
My research areas at the University of Florida extend to stochastic simulation methods and analysis as well as elements of wind engineering, specifically full-scale measurement of hurricane wind loads.
Looking to broaden my research experience in structural dynamics beyond wind loading, I chose to participate in the Summer Institute Program to learn more about seismic design and earthquake engineering, two topics not traditionally covered in our department’s curriculum. One of our faculty put me in contact with Masayoshi Nakashima, a Professor in the Disaster Prevention Research Institute (DPRI) at Kyoto University. Dr Nakashima arranged for me to work for Mitsumasa Midorikawa, the Research Director for International Codes and Standards at the Building Research Institute (BRI) in Tsukuba.
I spent the first month of my stay in Tsukuba in intensive language training and preparation for the experiment at the BRI. During the fifth week I moved to Kyoto to be closer to the DPRI. I spent the first week at the US-Japan Steel Workshop, and the remainder of my time was spent at the shake table.
I also participated in a supplemental program organized by the National Science Foundation. The Natural Hazard Mitigation Program in Japan, the prequel to the summer experience outlined below, is documented at http://www.nd.edu/~quake/nhmj/journal-fmasters.pdf.
Sudden Collapse due to Seismic Activity
Japan
possesses almost one half of the population of the US, and one-half of that
population lives in one of Japan’s three major cities: Tokyo, Osaka and Kobe.
These highly urbanized areas contain many houses considered substandard by
today’s building codes and technologies. Although these regions are in various
stages of gentrification, a gross portion of the housing is still at risk for
catastrophic structural damage during an earthquake.
During the Hyogen Nambu or Kobe earthquake in 1995, over 6,400 people perished in the 7.2 Richter magnitude earthquake. The close proximity of housing did not allow the homes to sway unimpeded. As a result, 90 percent of fatalities occurred from the collapse of traditional Japanese homes.
Retrofitting Traditional Japanese Homes
The dense population of Japan and its high frequency of seismic activity provided the impetus to study ways to protect homes against earthquakes. Individual retrofitting of traditional Japanese homes, however, is cost prohibitive, so the DPRI undertook examining various energy dissipation devices between homes.
In
conjunction with the Building Research Institute, we tested linkages between
single degree of freedom (SDOF) models that captured the average stiffness and
damping of real homes. Several energy dissipation devices were tested, including
foam inserts, air bladders and rubber straps.
Japanese research excels in its use of state-of-the-art data acquisition systems. During the experiments, we used a laser LVDTs, accelerometers, and a special photogrammetry system to measure displacements, velocities and accelerations. To my knowledge, the usage of the photogrammetry system was the first of its kind in a structural engineering experiment. The system utilized special cameras that were mounted above the shake table and recorded the movement of special reflectors on the tops of the models. The camera system allowed for a completely wireless setup on the table.
Determining the Best Solution for Energy Dissipation
On the shake table at the DPRI, we constructed the SDOF equivalent of six traditional Japanese homes and linked them in various combinations of energy dissipation devices. During my time, we tested each of the systems and hybrid combinations of the systems. Specifically, we looked at the relative displacements of the structures to each other.
At the time of my departure, the experiment was still underway, but the air bladder system showed the most promise. Significant data reduction and analysis will have to be completed before a definitive answer is available.
Acknowledgements
I would like to thank Professor Masayoshi Nakashima and Professor Mitsumasa Midorikawa for their extensive efforts to make me feel comfortable during my stay in Japan. They were a valuable source of information, and I am grateful for the opportunity to interact with them in and out of the laboratory.
Additionally, I would like to thank NSF Tokyo and JISTEC staffs for their guidance and organization. Their hospitality alone compels me to return to continue relations with my colleagues and superiors in Japan. I can only hope that my future work will serve to recompense all of the individuals that took care of my lodgings, education and excursions into the country. Thank you so very much.