2018 Volume 18 Issue 2 Pages 2_130-2_146
The nonlinear soil amplification model for the evaluation of response spectra is developed using strong ground motion records. This model transforms a linear amplification, which is prepared in advance at a specified site, to a nonlinear amplification according to the input level of bedrock motions. The model consists of two steps, and two functions are formulated for each step. One represents "elongation of predominant period" and the other "decrease of amplification". Functions describe a degree of nonlinearity with only one parameter, effective shear strain. According to the proposed function form, a nonlinear site amplification model for a simple two-layered ground model is made based on numerical analysis of sequential ground response. The ratios between amplifications from a proposed model and precise waveform analysis are constant and close to 1.0. On the basis of the result, it is verified that the proposed model have applicability to the evaluation of nonlinear soil amplification. Next, another model is made using strong ground motion records at K-NET Toyosato site in the northeast region of Japan. The ground of this site is considered to be almost two-layers. In the period shorter than predominant period, the amplification evaluated with the model developed in this study shows good agreement with those of previous studies. In the period longer than predominant period, the model of this study shows the increase of amplification as a result of elongation of predominant period, which the models of previous studies do not describe. It is concluded that the proposed model is useful for the estimation of the nonlinear soil amplification.
