Nonlinear Sway–Rocking Stiffness of Pile Foundation

Abstract

Substructure approach is a well-accepted and simplified method for analysis of seismic soil–structure interaction (SSSI) problems. Past studies suggested equivalent springs and dashpots to represent soil-foundation system in substructure analysis. The primary limitation of this analysis is that foundation behaviour is considered to be elastic, and hence, nonlinear behaviour of foundation could not be accurately predicted. As a result, accurate prediction of seismic response of structure incorporating SSSI condition may be missed out due to this limitation. In this context, present study attempts to propose nonlinear dynamic stiffness of equivalent pile–soil springs which may be used to capture the sway–rocking mode of vibration of the whole system. Three-dimensional (3D) finite element model (FEM) of single free head pile is primarily analysed considering coupled static horizontal and moment load at the top of pile which finally utilized to generate dynamic nonlinear stiffness of pile group foundation by multiplying frequency and dynamic group interaction factor with nonlinear stiffness obtained from static FEM analysis. The proposed dynamic nonlinear stiffness of single pile with respect to pile deformation is presented in a simplified non-dimensional form as a function of linear stiffness. Non-dimensional results presented in this present study may provide ready solution to carry out SSSI studies for pile supported structure considering nonlinear behaviour of foundation.