4 tornadoes occurred on May 6^th, 2012 in the north part of the Kanto area, Japan. Of these, the one that struck Joso city and Tsukuba city in Ibaraki prefecture was the strongest. According to the JapanMeteorological Agency, it was 0.5 km wide, 17 km long, and Fujita scale level 3 [1]. According to local government statistics from Ibaraki prefecture, 1 person was killed, 39 were injured, and 1,133 structures were damaged – 207 destroyed, 258 half destroyed, and 668 damaged [1]. The Wind Engineering Research Center of Tokyo Polytechnic University carried out field investigations in damaged areas onMay 7, 8, 9, and 13. Based on its results, Fujita scale strength was estimated at 4. Based on our damage investigation results, we deduce scenarios and estimate wind speed when the 2 structures this paper focuses on were catastrophically damaged.

1. [1] Japan Meteorological Agency, “Brief Report of field survey on the damage due to tornado occured in Joso city and Tsukuba city, Ibaraki Prefecture in March 6th , 2012” (in Japanese), http://www.data.jma.go.jp/obd/stats/data/bosai/tornado/2012050603/ref01.pdf [accessed July 16, 2012]
2. [2] J. D. Holmes, C. J. Baker, and Y. Tamura, “Tachikawa number: A proposal,” Journal of Wind Engineering and Insudtrial Aerodynamics, Vol.94, pp. 41-47, 2006.
3. [3] H. Takeuchi, J.Maeda, and H. Kawashita, “The Overshoot of Aerodynamic Forces on a Railcar-Like Body under Step-Function-Like GustyWinds,” BBAAVI International Colloquium on: Bluff Bodies Aerodynamics & Applications Milano, Italy, pp. 20-24, July 2008.
4. [4] Japan Housing and Wood Technology Center, “Allowable Stress Design Method of Conventional Post and Beam Structure,” 2008 (in Japanese).