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Many buildings in Japan currently have a base-isolation system with a low stiffness that is designed to shift the natural frequency of the building below the frequencies of the ground motion due to earthquakes. However, the ground motion observed during the 2011 Tohoku earthquake contained strong long-period waves that lasted for a record length of 3 min. To provide a novel and better solution against the long-period waves while maintaining the performance of the standard isolation range, the exploitation of the characteristics of nonlinear damping is proposed in this paper. This is motivated by previous studies of the authors, which have demonstrated that nonlinear damping can achieve desired performance over both low and high frequency regions and the optimal nonlinear damping force can be realized by closed loop controlled semi-active dampers. Simulation results have shown strong vibration isolation performance on a building model with identified parameters and have indicated that nonlinear damping can achieve low acceleration transmissibilities round the structural natural frequency as well as the higher ground motion frequencies that have been frequently observed during most earthquakes in Japan. In addition, physical building model based laboratory experiments are also conducted, The results demonstrate the advantages of the proposed nonlinear damping technologies over both traditional linear damping and more advanced Linear-Quadratic Gaussian (LQG) feedback control which have been used in practice to address building isolation system design and implementation problems. In comparison with the tuned-mass damper and other active control methods, the proposed solution offers a more pragmatic, low-cost, robust and effective alternative that can be readily installed into the base-isolation system of most buildings. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, based on field measurements for the passage of the Shinkansen high speed trains on viaducts, the author reports the induced ground vibration features at distinctly different sites: one site is characterized by a deep soft soil and the other by a shallow soft soil both of which lie on stiff bottom. The conventional vibration assessment is normally addressed to the vibration levels based on acceleration maxima. However, in view of the vibration reception by nearby residents, firstly, a detailed investigation is attempted on the recorded time histories and on their Fourier spectra, locating the so-called low frequency vibration generation at the former site and such vibration impediment at the latter site. Then, theoretical consideration is to clarify the Shinkansen-train induced ground vibrations from a viaduct. The characterization based on the wave theory using the thin layer method reveals that, depending on the depth of surface layer, the ground-borne vibration is of significantly low frequency wave modes of dispersive propagation when it is deep or it makes the wave modes shifted towards higher frequency range when it is shallow. This finding makes an important element to better predict and assess vibration level and to develop barriers against it for mitigation. [Copyright &y& Elsevier]