Abstract
Proposed is a nonlinear earthquake response analysis in frequency domain. Stress-strain relations in frequency domain are defined by the vector spectrum method, i. e., Fourier transforms of stress and strain in a complex plane, and relationships between stress-strain behavior in frequency domain and actual stress-strain curve are investigated. Frequency range where response of subsoil is affected strongly by the nonlinear behavior is evaluated by comparing the unsteady spectrum with a nonlinear effective function that is defined as the first derivative of an amplification factor with respect to a shear wave velocity. A method to evaluate effective strains in frequency domain from the maximum shear strain in time domain is proposed by combining above two findings. The proposed method is compared with conventional equivalent linear methods at two sites where strong motion vertical array records were obtained. The proposed method always shows better agreement with other methods.
