The duration of strong motion exceeding the bridge design spectra in the bridge design specification in Japan is evaluated for the 2016 Kumamoto Earthquake. The structural response duration is defined as the total threshold interval of the velocity response envelope calculated for a viscously damped (5%) single-degree-of-freedom oscillator with various natural period. The prescribed design spectra are employed as frequency-dependent thresholds. The ground acceleration records observed at the K-NET and KiK-net stations during the Kumamoto earthquake are used for the analysis. Spectrum representations of the duration and number of cycles are obtained for four representative ground motion observation stations. The distribution maps of the duration are also presented for the strong motion observation stations in the Kumamoto prefecture.

1. [1] B. A. Bolt, “Duration of strong ground motions,” Proc. of the 5^th World Conference on Earthquake Engineering, Vol.1, Acapulco, pp. 1304-1313, 1973.
2. [2] M. D. Trifunac, “Response envelope spectrum and interpretation of strong earthquake ground motion,” Bulletin of the Seismological Society of America, Vol.61, No.2, pp. 343-356, 1971.
3. [3] R. Dobry, I. M. Idriss, and E. Ng, “Duration characteristics of horizontal components of strong-motion earthquake records,” Bulletin of the Seismological Society of America, Vol.68, No.5, pp. 1487-1520, 1978.
4. [4] J. J. Kempton and J. P. Stewart, “Prediction equations for significant duration of earthquake ground motions considering site and near-source effects,” Earthquake Spectra, Vol.22, No.4, pp. 985-1013, 2006.
5. [5] J. J. Bommer, P. J. Stafford, and J. E. Alarcón, “Empirical equations for the prediction of the significant, bracketed, and uniform duration of earthquake ground motion,” Bulletin of the Seismological Society of America, Vol.99, No.6, pp. 3217-3233, 2009.
6. [6] J. J. Bommer and A. Martinez-Pereira, “Strong-motion parameters: definition, usefulness and predictability,” Proc. of the 12^th World Conference on Earthquake Engineering, Auckland, New Zealand, Paper No.0206, 2000 (on CD-ROM).
7. [7] V. Perez, “Spectra of amplitudes sustained for a given number of cycles: an interpretation of response duration for strong-motion earthquake records,” Bulletin of the Seismological Society of America, Vol.70, No.5, pp. 1943-1954, 1980.
8. [8] K. Kawashima and K. Aizawa, “Earthquake response spectra taking account of number of response cycles,” Earthquake Engineering and Structural Dynamics, Vol.14, No.2, pp. 185-197, 1986.
9. [9] T. Ishii, “A Study on response duration time spectra of earthquake motions in Tokyo,” Proc. of the 14^th World Conference on Earthquake Engineering, Beijing, China, Paper No.02-0020, 2008 (on CD-ROM).
10. [10] N. Nojima, “Spectrum representation of strong motion duration using total threshold intervals of velocity response envelope and its application,” Journal of Japan Association of Earthquake Engineering, Vol.15, No.1, pp. 1-17, 2015 (in Japanese).
11. [11] N. Nojima, “Frequency-dependent strong motion duration using total threshold intervals of velocity response envelope,” Proc. of the 10^th Pacific Conference on Earthquake Engineering, Sydney, New South Wales, Australia, Paper No.165, 2015.
12. [12] J. Hancock and J. J. Bommer, “The effective number of cycles of earthquake ground motion,” Earthquake Engineering and Structural Dynamics, Vol.34, No.6, pp. 637-664, 2005.
13. [13] J. Hancock and J. J. Bommer, “A state-of-knowledge review of the influence of strong-motion duration on structural damage,” Earthquake Spectra, Vol.22, No.3, pp. 827-845, 2006.
14. [14] K. Kameda, “Evolutionary spectra of seismogram by multifilter,” Journal of the Engineering Mechanics Division, ASCE, Vol.101, No.6, pp. 787-801, 1975.
15. [15] M. D. Trifunac and A. G. Brady, “A Study on the duration of strong earthquake ground motion,” Bulletin of the Seismological Society of America, Vol.65, No.3, pp. 581-626, 1975.
16. [16] Japan Road Association, “Specifications for highway bridges, Part V, Seismic design,” March 2012 (in Japanese).
17. [17] The National Research Institute for Earth Science and Disaster Prevention (NIED). K-NET, KiK-net, http://www.kyoshin.bosai.go.jp/kyoshin/, http://www.kyoshin.bosai.go.jp/kyoshin/topics/ Kumamoto_201604 16/kumamoto201604 160125.pdf [in Japanese, accessed August 1, 2017]
18. [18] Ministry of Land, Infrastructure and Transportation and Tourism (MLIT), “Summary of damage to road structures,” 2016, https://www.mlit.go.jp/common/001136053.pdf [in Japanese, accessed August 1, 2017]
19. [19] Y. Takahashi, “Damage to bridge structures cause by the 2016 Kumamoto earthquake,” The special session for report of Kumamoto Earthquake at the 2016 annual meeting of JSCE, Earthquake Engineering Committee, Japan Society of Civil Engineers, 2016, http://committees.jsce.or.jp/eec2/ [in Japanese, accessed August 1, 2017]
20. [20] Reconnaissance Team for Earthquake Damage to Road Steel Structure, “A quick report of reconnaissance team for the 2016 Kumamoto earthquake,” Steel Structure Committee, Japan Society of Civil Engineers, 2017 (in Japanese).
21. [21] T. Ikeda, K. Konagai, and T. Kiyota, “Preliminary report of geotechnical and structural damage along the surface rupture in Nishihara Village caused by the April 16th, 2016 Kumamoto earthquake,” JSCE Journal of Disaster FactSheets, Japan Society of Civil Engineers FS2016-E-0004, p. 9, 2016, http://committees.jsce.or.jp/disaster/FS2016-E-0004 [accessed August 1, 2017]