考虑土体非线性的地下结构抗震计算中阻尼比的取值问题

The value of damping ratio in seismic calculation of underground structures considering soil nonlinearity

为了简化地下结构抗震计算,通过设置简化边界来吸收地基中波的辐射耗能,简化边界为竖向约束、水平自由,并从理论上分析了平面问题侧向边界的合理性;土体的内摩擦通过土体的阻尼耗能和塑性滞回耗能表示,讨论了土体阻尼比的合理取值;通过一个典型案例对比了土体非线性计算和等效线性化计算的结果。计算结果表明:侧向简化边界可以满足抗震计算要求;土体非线性计算时,土体阻尼比要采用土体初始剪切模量对应处的阻尼比。

For simplicity,the local artificial boundary was set as simple constraints,which was vertical constraints and horizontal freedom.The simplification of lateral boundary can be theoretically justified based on plane problem.Internal friction of soil was shown by damping energy dissipation and plastic hysteretic energy dissipation.The reasonable value of damping ratio of soil was analyzed.The results of two methods,including soil equivalent linear model and nonlinear soil model,were evaluated and compared by dynamic time history method through a selected benchmark numerical example.It was shown that generally the simplified lateral boundary can meet the requirement in seismic calculation and the soil damping ratio should adopt the value corresponding to the soil initial shear modulus when considering soil nonlinearity by nonlinear soil model.