An equivalent linear method considering frequency-dependent soil properties for seismic response analysis

Equivalent linear method was widely used in the seismic response analysis of soil deposits because of its simplicity in preparing the input data and the stability of numerical calculation,but some problems,such as underestimating the Fourier spectrum amplification ratio at high frequency and overestimating the peak ground accelerations,would appear in its practical application.The theoretical background of equivalent linear methods considering frequency-dependent soil properties was shown.Downhole array records were used and fitting lines of the strain spectra were analyzed.A new method considering frequency-dependent soil moduli and damping was proposed using the new spectral fitting line of the strain.Based on the computer code DYNEQ and the above-mentioned theories,two computer programs were compliled.Three sites were analyzed using these programs and the results were compared with the downhole array records.The prediction with the methods considering frequency dependent soil properties was better than that of the original equivalent linear method SHAKE,and they were different from each other in the analysis details.The results obtained by the proposed method agreed well with the downhole array records.