A Methodology for Nonlinear Soil-Structure Interaction Effects Using Time-Domain Analysis Techniques
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This series includes technical reports prepared by faculty, students and staff who are associated with the John A. Blume Earthquake Engineering Center at Stanford University. While the primary focus of Blume Center is earthquake engineering, many of the reports in this series encompass broader topics in structural engineering and materials, computational mechanics, geomechanics, structural health monitoring, and engineering life-cycle risk assessment. Each report includes acknowledgments of the specific sponsors for the report and underlying research. In addition to providing research support, the Blume Center provides administrative support for maintaining and disseminating the technical reports. For more information about the Blume Center and its activities, see https://blume.stanford.edu.
The dynamic response of rigid foundations on an elasto-viscoplastic half-space is investigated in the context of nonlinear finite element (FE) analysis. A deviatoric viscoplastic theory with a linear combination of isotropic and kinematic hardening is used to model the soil constitutive response. Large-scale nonlinear FE computations are made feasible by the use of a composite Newton-POG iteration technique, which requires the factorization of the consistent tangent operator no more than once during the solution process. Time-domain analyses are used to investigate the nonlinear responses of vertically oscillating circular, square, and rectangular foundations to harmonic loads, using two- and three-dimensional FE modeling. It is shown that for low frequency excitations, resonance is created which amplifies the motion of the foundation at amplitudes well above those obtained at the zero-frequency leveL In addition, horizontal, rocking, and torsional vibration modes of strip and square foundations are considered using the same methodology developed for vertically oscillating foundations. The foundation responses for horizontal, rocking, and torsional modes are characterized by increased vibrational amplitudes due to material stiffness degradation. Furthermore, one or more resonance frequencies are created which 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 horizontal modes. In contrast, nonlinear soil effects are shown to be dominant over a much narrower range of excitation frequencies for the vertical and rocking modes.
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