Damping matrix coefficient selection in explicit calculation of soil layer seismic response

Abstract:

The method for forming damping matrix in explicit algorithm of LS-DYNA in the analysis of seismic response of soil layer was studied in this paper. First, based on the assumption of mass-proportional damping matrix, the influence on the damping ratio of each mode was discussed. Then the analysis methods of time domain and frequency domain were applied in the seismic response calculation of three different types of soil layer. Through the comparison of calculation results between time domain and frequency domain, the effects on calculation results by using mass-proportional damping matrix were explored. Finally the determination of damping coefficient of the mass-proportional was proposed. Only when the seismic displacement reaction of soil layer is calculated or when the fundamental frequency of soil layer is higher than the input seismic wave excitation frequency of the under lying bedrock to calculate the soil seismic acceleration response, it is feasible to apply the fundamental frequency of soil layer to determine the mass-proportional damping coefficient. When the fundamental frequency is close to and especially much lower than the excitation frequency of input seismic wave, substituting the arithmetic mean of soil layer fundamental frequency and response spectrum peak frequency of input seismic wave for the soil layer fundamental frequency is recommended to calculate the mass-proportional damping coefficient. This method can effectively improve the calculation accuracy.