Influence of nonlinear Lysmer dashpots on seismic soil-structure interaction: a comparative finite element study

Abstract In the present study, the influence of nonlinear Lysmer dashpots on seismic soil structure interaction is investigated using three dimensional hexahedral finite element models. Nonlinear Lysmer absorbing boundaries are compared with free and fixed boundaries under seismic excitation, considering both soil structure interaction and free field configurations. The effects of the boundary formulations are evaluated through time history responses, amplification factors, maximum accelerations, and maximum displacements. The results demonstrate that the influence of nonlinear dashpots is significant primarily when the ratio between the width and height of the finite element computational domain is lower than 20, whereas their influence becomes comparatively limited for larger ratios. The investigated seismic excitation corresponds to the Athens 1999 earthquake accelerogram, characterized by a dominant pulse like component. The amplification factor associated with absorbing boundaries does not decrease monotonically, mainly due to the development of standing wave patterns within the computational domain. In contrast, the soil amplification ratio is only slightly affected by the adopted boundary conditions and is predicted with acceptable accuracy for all investigated cases. Overall, the results consistently demonstrate the fundamental characteristics of seismic soil structure interaction, including modifications of equivalent boundary loads and amplification of structural and soil displacements. The findings indicate that the nonlinear formulation of Lysmer dashpots should receive particular consideration when relatively narrow computational domains are employed in seismic finite element analyses.