An Effective Local Absorbing Boundary for 3D FEM Time Domain Analyses

The aim of this paper is to investigate and develop alternative methods for analyzing transient problems in dynamic soil-structure interaction, (SSI) within the FEM context. Development of a simple and efficient FEM procedure for the solution directly in the time domain of SSI problems is the main issue. Considering Direct Method of analysis, a new formulation of local transmitting boundaries for transient three-dimensional (3D) FEM analysis is presented based on the radiation criterion and strength-of- materials theory. These numerical devices can be considered as doubly asymptotic, (DA) approximations and are given in terms of first order differential operators. Different formulations for volume and surface waves are considered. A computer code employing an implicit FEM for solving 3D elastic wave propagation problems is developed to investigate the effectiveness of the proposed boundary conditions, (BC’s). Numerical examples for homogeneous hafspace in full 3D are presented in comparison to extended mesh and fundamental solutions, a classical approach. As the effort for implementing them is the same as for the impedance BC, standard assembly procedure can be used. Due to the local nature they also preserve the overall structure of the global equations of motions