土层地震反应显式计算中阻尼矩阵系数的选取

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

摘要:

针对LS-DYNA程序关于土层地震反应显式计算中形成阻尼矩阵的方法开展讨论。首先，讨论了采用质量比例阻尼矩阵假定对各阶振型阻尼比带来的影响；然后分别应用时域和频域分析方法对三种不同类型土层的地震反应进行计算，通过比较时域和频域的计算结果，探讨了采用质量比例阻尼矩阵假定对计算结果的影响；最后，对质量比例阻尼系数的确定提出了建议：当仅计算土层地震位移反应或当土层基频高于下卧基岩输入地震波的主要激励频率条件下计算土层地震加速度反应时，以目前由土层基频计算质量比例阻尼系数的方法是可行的；但当土层基频接近于，特别是远低于输入地震波的主要激励频率时，应用土层基频和输入地震波反应谱峰值频率的算术平均值替代土层基频计算质量比例阻尼系数，可有效提高土层地震加速度计算精度。

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.