Equivalent linearization parameters of soil-MDOF structure systems subjected to pulse-like earthquakes

摘要

In seismic design codes and documents, the period and damping ratio of a linear fixed-base single degree-of-freedom (SDOF) system are tuned to return the dynamic response of a given nonlinear fixed-base SDOF structure through a so-called equivalent linearization method. The period and damping ratio of the equivalent linear system are referred to as equivalent or effective linear parameters (ELPs). These ELPs may vary due to higher modes of the superstructure, the soil-structure interaction (SSI), or the pulse effects of the earthquake ground motions. Hence, this paper focuses on an extension of the equivalent linearization concept to nonlinear soil-multi-story structure systems under pulse-like earthquakes where the whole system is substituted with an equivalent fixed-base SDOF oscillator. To achieve this goal, the underlying soil is assumed as a homogeneous half-space medium and the superstructure is modeled as a nonlinear multiple degrees-of-freedom (MDOF) shear building assuming bilinear behavior for each story. Non-dimensional frequency and aspect ratio parameters are used to enforce the SSI effects in the system. The seismic responses are determined under an extensive ensemble of 91 pulse-like earthquakes for two different ranges of fixed-base structure-to-pulse period ratios, and the ELPs are determined for a range of soil-structure systems throughout a statistical framework. It is found that higher modes have decreasing effects on the ELPs of soil-MDOF structure systems, while the effects of the strain-hardening ratio of each story are insignificant. In addition, the impulsive nature of the ground motions strongly affects the ELPs, and this influence is far more pronounced for structure-to-pulse period ratios between 0.8 and 1.2, i.e., very close to the resonance of the first mode of the superstructure. (C) 2018 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.