NONLINEAR LATERAL, ROCKING, AND TORSIONAL VIBRATION OF RIGID FOUNDATIONS

Two- and three-dimensional finite element (FE) analyses are performed to investigate the influence of nonlinear soil behavior on the dynamic response of harmonically excited rigid foundations. Lateral, rocking, and torsional vibration modes are considered. An elastoviscoplastic constitutive model with kinematic hardening is assumed for the foundation soil, and computations are done implicitly in the time domain. The foundation responses for lateral, rocking, and torsional modes are characterized by increased vibrational amplitudes due to material stiffness degradation. Furthermore, resonance frequencies are created that resemble those observed for vertically oscillating finite-size foundations. Nonlinear soil effects are shown to be dominant over a wide range of excitation frequencies for foundations vibrating in torsional and lateral modes. In contrast, nonlinear soil effects are shown to be dominant over a much narrower range of excitation frequencies for the rocking mode. The methodology presented in this paper is useful for nonlinear vibration and transient soil-structure interaction (SSI) analysis.