免震・連結制振ハイブリッド構造の振動低減のメカニズム

It is recognized that a base-isolated building exhibits a large response to a long-duration, long-period ground motion and an interconnected building system is not necessarily effective for a pulse-type ground motion. To compensate for each deficiency, a new hybrid passive control system is investigated in which a base-isolated building is connected to another building (free wall) with oil dampers. It is shown that the mechanism of response reduction in the proposed hybrid passive control system is closely related to the property of natural frequency and damping ratio with respect to increased capacity of connected dampers in a translation mode and a meeting-parting mode.First of all, the model H (hybrid) and the model N (normal) are defined in Section 2 and the natural frequencies and damping ratios of these models are formulated in Section 3 through the complex eigenvalue analysis. There are three cases (A, B, C). Case A is the case where all four eigenvalues are complex values, Case B is the case where two are complex and the other two are real and Case C is the case where all four eigenvalues are real. The total damping coefficient of the connecting dampers is increased in order to investigate the properties of the models H and N. It is shown that the three cases (Case A-C) appear corresponding to the range of the total damping coefficient of the connecting dampers.In Section 4, it is demonstrated that there are two eigenmodes, called the translational mode and the meeting and parting mode, for the infinite total damping coefficient of the connecting dampers. The eigenmode for a finite total damping coefficient of the connecting dampers corresponding to the translational mode is called ‘a mode toward the translational mode’ and that for a finite total damping coefficient of the connecting dampers corresponding to the meeting and parting mode is called ‘a mode toward the meeting and parting mode’. The eigenvalues and eigenmodes of the mode toward the translational mode and the mode toward the meeting and parting mode are derived in Section 4.2 and 4.3.In Section 5, the response characteristics of both models (model H and model N) to the pulse-type earthquake ground motions and the long-period, long-duration ground motions are investigated. It is shown that the relation between the fundamental natural period of the main building and the predominant period of the long-period, long-duration ground motions plays a key role in the understanding of the respon