B-Spline Impulse Response Functions for Transient SSI Analysis of Pile Foundations

The advent and consequential advancements in geotechnical earthquake engineering has made soil-structural analysis (SSI) an important component in the analysis and design of earthquake resistant structures. The filtering effects of pile foundations which reduces the seismic demand on pile-supported superstructure when they are subjected to seismic waves have been investigated and confirmed by several researchers in the last 40 years. To this end, several methods of analyzing the effects of SSI have been developed over the years. From the simplified Winkler model to the more robust finite element method (FEM) and boundary element method (BEM), researchers and structural engineers alike have sought to address the SSI phenomenon. The results produced by such analysis has either been computationally expensive, thereby prohibiting more routine application, as is with the case of the FEM and BEM or the results are outside the scope of more complex structures that they cannot be relied upon, as is with the case of analytical methods that depend on the simplified lumped parameter models or Winkler model. Therefore, there is need for a solution that strikes a balance between simplicity and computational cost without sacrificing accuracy. This work presents a simplified, yet accurate model of pile foundation-soil system for the dynamic analysis of structures including SSI effects. The simplified model is based on solutions that reproduce the characteristic B-spline impulse response functions (BIRF) of 3D continuous soil-pile foundation systems, as obtained from the FEM analysis. The proposed simple, yet accurate model, is used within the framework of B-spline impulse response techniques and can be coupled directly to other commonly used time-domain solutions.