Evaluation of Non-Linear Site Effects using Kik-Net Japanese database

Student: Surendra Kumar Singupalli
Supervisors: Prof. Pierre-Yves Bard, Prof. Fabrice Cotton, and Dr. Luis Fabian Bonilla

ABSTRACT

In recent years, debate over Non-Linear Site Effects is discussed a lot in the engineering seismology field. Many feel that non-linearity exists, but the degree of non-linearity is still an open question. Nonlinear site effects whereby the increase in damping and reduction in shear modulus as input strength increases are commonly recognized in the dynamic loading of soils from geotechnical models. With recent findings, it is now accepted that the nonlinear site effects are more common than previously recognized in strong-motion seismology.

For the purpose, this study aimed to evaluate non-linear site effects using the model proposed by Cotton et al. 2008 (based on Kik-Net database). The site effects were primarily evaluated for Soil classes B and C, at five spectral ordinates i.e. 100 Hz (PGA), 26 Hz, 5.91 Hz, 1.06 Hz and 0.51 Hz. Soil Non-Linearity was observed at high frequencies (i.e. at 5.91 Hz, 26 Hz, and 100 Hz) for soil C (EC 8 classification), i.e. low velocity soil layers. Furthermore it can be concluded that the soil non-linearity is observed for input strong rock motions beyond 60 cm/s2 (approx.). This study further computed amplification factors, showing characteristics which are recognized previously in the studies by Steidl (2000). It was found that low amplitude motions get highly amplified with increasing frequency and decrease with increasing input rock motion. The average ratios of amplification show the same trend. At 100 Hz, soil C showed an amplification factor of 6.8. Furthermore, it was found that the computed residuals at different frequencies always show positive correlation and never showed negative correlation. It might suggest that there exist dependency of residuals on frequency.

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