Premium
Soil‐structure system frequency and damping: Estimation from eigenvalues and results for a 2D model in layered half‐space
Author(s) -
Fu Jia,
Liang Jianwen,
Todorovska Maria I.,
Trifunac Mihailo D.
Publication year - 2018
Publication title -
earthquake engineering and structural dynamics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.218
H-Index - 127
eISSN - 1096-9845
pISSN - 0098-8847
DOI - 10.1002/eqe.3055
Subject(s) - soil structure interaction , embedment , foundation (evidence) , stiffness , mathematics , mathematical analysis , modal , eigenvalues and eigenvectors , bedrock , structural engineering , damping ratio , geotechnical engineering , geology , engineering , finite element method , physics , vibration , acoustics , materials science , quantum mechanics , geomorphology , archaeology , polymer chemistry , history
Summary This paper presents a formulation for estimation of the frequency and damping of a soil‐structure interaction system based on the classical modal analysis and solving the system eigenvalue problem. Without loss of generality, the structure is represented by a single degree of freedom oscillator, while the soil effects are included through impedance functions for in‐plane motion of a 2D rigid foundation. For the results presented in this paper, the impedance functions were computed by the indirect boundary element method for a rectangular foundation embedded in a soil layer over elastic bedrock. The study shows that the classical modal‐analysis approach works well, with the exception of squat, stiff structures, even though the impedance functions are frequency‐dependent and the soil‐structure interaction system does not possess normal modes. The study also shows that system frequency and damping are independent of the wave passage effects, contrary to findings of some previous studies, and that the site conditions, represented by the soil‐layer thickness and stiffness contrast between bedrock and soil layer, have significant influences on both system frequency and system damping. Finally, the paper examines the accuracy of some of the simple methods for estimation of these two system parameters and comments on some conflicting conclusions of previous studies about the effects of foundation embedment.