软硬交互横向不均匀场地地震反应分析

软硬交互横向不均匀场地十分常见,其在强震作用下的地震反应对工程结构的安全有着重要影响,然而目前还很少有针对该场地地震反应分析的研究。基于精确动力刚度矩阵和均布荷载动力格林函数的间接边界元方法,经快速傅里叶逆变换,在时域内求解了层状半空间中软硬交互横向不均匀场地的地震反应问题。求解中将模型分解为含较硬介质的层状半空间域和较软介质域,同时将总波场分解为自由波场和散射波场两部分,通过在相应边界上施加斜线和水平线虚拟均布荷载,进而求解动力格林函数以模拟散射波场,自由波场可由直接刚度法方便求得。验证了方法的正确性,检验了求解模型的收敛性,进而开展了相应的数值计算分析,着重讨论了介质参数和软硬交界面倾角对场地地震反应的影响。研究表明:软硬交互场地中,较大的地表地震动响应发生在较软介质侧;软硬交界面的存在使得场地地表加速度响应发生突变,突变程度受介质参数和交界面倾角的影响显著;随着介质参数差异和交界面倾角的增大,地表加速度峰值增大,反应谱曲线显示短周期成分变得更为丰富,对基岩地震动的放大作用增强;软硬交界面对场地地表地震反应的影响主要在交界面外的两倍介质层厚度范围。

Seismic response analysis of lateral uneven sites with soft-hard connected media

The lateral uneven site with soft-hard connected media is very common, and its seismic response under strong earthquakes has an important impact on the safety of engineering structures. However, studies have seldom been reported to investigate the seismic response of soft-hard connected sites. Based on the indirect boundary element method combined with the exact dynamic stiffness matrix and Green's functions of uniformly distributed loads, the seismic response of soft-hard connected sites in a layered half-space is solved in time-domain via the fast Fourier inverse transform. In the solution, the model is divided into a harder medium of layered half-space region and a softer medium region, while the wavefield is classified into two parts: free field and scattered field. The diffraction response can be simulated by the Green's function of inclined and horizontal fictitious distributed loads acting on corresponding boundaries, and the free field response can be easily solved by the direct stiffness method. The accuracy of the proposed method is verified, and the convergence of the solution model is tested. Numerical calculations are performed to analyze the influences of medium parameters and soft-hard interface dip angles in the seismic response. The results show that in the soft-hard connected site, the stronger ground motion response occurs in the softer medium region. The existence of an soft-hard interface leads to a sudden change in acceleration response, and its sensitivity is significantly affected by medium parameters and interface dig angles. With the increase of difference in the medium parameters and interface dig angles, the peak ground acceleration increases, the response spectrum curve shows more abundant short-period components, and the amplification effect on bedrock motion is enhanced. The influences of soft-hard interface on the surface seismic response of the site are mainly within twice the thickness of the medium layer outside the interface.