3D soil-structure interaction analysis with a combined substructure-FEM under external forces and seismic waves

This paper presents a simple methodology for studying soil-structure interaction problems. Based on the substructure approach, the unbounded soil beneath the foundation has been removed. The foundation's impedance matrix and the driving force vector due to seismic waves have been applied to the superstructure. Foundation-soil impedance functions have been reproduced by utilizing sets of springs and dashpots with elastic and damping frequency-dependent properties. The superstructures have been discretized with refined finite beam elements derived with the Carrera Unified Formulation. Vertical, horizontal, rocking and torsional vibrations of the superstructure-soil system have been investigated by considering soft, intermediate, stiff and rigid soils. Displacement and stress values of the flexible-base superstructures have been compared with those obtained for the fixed-base configuration. For validation purposes, the obtained results have been assessed with solutions available in the literature and with those provided by the ASCE-7 building code. In all cases, significant agreements have been observed. Higher-modes frequencies and responses have been obtained for the flexible-base superstructures which could be very useful for modal analyses including SSI effects.