Three-Dimensional Indirect Boundary Element Method Formulation for Dynamic Analysis of Frames Buried in Semiinfinite Elastic Media

This paper presents a formulation of the indirect boundary element method based on the principle of virtual work for the dynamic analysis of frame structures buried in semi-infinite elastic media. The present formulation, which falls in the category of symmetric Galerkin boundary element methods, leads to symmetric stiffness matrices for the continuum that may be defined in terms of conventional structural analysis variables (i.e., generalized displacements and lumped forces). It is shown that, in the context of the present formulation, rotation degrees of freedom may readily be introduced in the interpolation scheme with very little additional computational effort. The consistency of the present formulation with well-established results is assessed by comparing the predictions for the static and dynamic stiffness of single piles with other results from the literature. Finally, the dynamic stiffness of a single buried frame under vertical and horizontal loading is studied. The analysis shows that the stiffness of the full frame may not always be accurately estimated by means of results for single piles, even when dynamic interaction factors are used.