Substructure method revisited for analyzing the dynamic interaction of structures with embedded massive foundations

This paper proposes a new simple approach for assessing dynamic soil-structure interaction effects on structures supported by embedded massive foundations. The classical substructure method was revisited by proposing an exact decomposition approach which allows performing the inertial interaction analysis of the superstructure without modeling foundation and soil, which are replaced by properly defined impedances. The proposed approach requires redefinition of simplified formulas for both the dynamic stiffnesses and the kinematic interaction factors, which are referred to the top of the massive foundation. Accurate expressions for the complex impedances were derived based on rigorous finite-element results. The same formulas were used to calibrate a four-spring model for the analysis of the kinematic interaction problem, resulting in different expressions for the kinematic interaction factors depending on the adopted assumptions. The proposed approach, in conjunction with the novel formulas for impedances and kinematic factors, was applied to the case of bridge piers on caisson foundations, and the results were more accurate than those of the existing simplified procedures.