Abstract
Accuracy of earthquake response analyses of ground is examined focusing on damping. In order to compare frequency domain analysis and time domain analysis under the same condition, functions to consider various frequency dependent damping are installed in the improved equivalent linear analysis, and modal damping, which has more frequency in determining damping with respect to frequency, is installed in the dime domain analysis. Moreover, a method to build modal damping in the elastic base problem is proposed. Comparisons between frequency domain and time domain analyses and between constant damping and damping proportional to frequency are made by an example ground under both elastic and nonlinear conditions. It is found that both frequency domain and time domain analysis give nearly identical result under elastic response, which indicates that modal damping can be used for frequency dependent problem in the time domain analysis. In the comparison of nonlinear analysis, behaviors are also almost identical in frequency lower than several Hz, and slight difference appears in the high frequency regions. In addition, proportional damping has a tendency to evaluate maximum strain or maximum displacement smaller than constant damping.
