摘要(英) |
Conventional isolations exhibit a linear relationship between the restoring force and displacement, resulting in a fixed isolation frequency. However, when the dominant frequency of seismic excitation is close to the isolation frequency, the resonance will occur and the isolation system may be ineffective. To address this issue, numerous studies have been conducted on isolation systems with nonlinear restoring force. One such system is the eccentric rolling isolation system (ERIS), which possesses nonlinear restoring force by using the concept of eccentricity. Previous studies of ERIS have proven that ERIS exhibits a lower acceleration response compared to linear isolation systems during near-fault earthquakes. Furthermore, the eccentric rolling isolation system with the convex guide (CERIS) which is an improvement of ERIS by adding a convex guide beneath the ERIS has been proposed. CERIS retains the characteristic of nonlinear restoring force and also enhances the isolation performance. However, previous studies of CERIS focus on structural isolation applications, thus neglecting the influence of the inertial effects of circular isolators and the conceptual mechanism only effective for unidirectional input. For equipment isolation applications, the mass of the equipment is close to that of circular isolators, therefore the inertial effects significantly affect the isolation performance. Additionally, real earthquakes should be bidirectional inputs, which were not adequately considered in previous studies. Hence, this study proposes an investigation of the CERIS considering the influence of isolator inertia and extends the unidirectional mechanical system to a bidirectional one by using orthogonal stacking to satisfy the requirements of practical applications. In the unidirectional experimental setup, the isolation platform is eccentrically pin connected to the circular isolator, and the target object is mounted on the isolation platform. The convex guide with a fixed radius of curvature is assembled beneath each circular isolator. This study derives the equations of motion considering the mass of the circular isolator by the energy method and and the Coulomb friction model is used to simulate the energy dissipation of the system. Through parameter sensitivity analysis, the effects of system design parameters, including eccentricity ratio, radius ratio, circular isolator radius, and mass ratio on the horizontal and vertical dynamic behavior of the system. In the simulation of forced vibrations, several seismic waves including near-fault and far-field motions are considered and compared with linear isolation systems to perform the superior seismic performances of the CERIS with various design parameters. Finally, biaxial shaking table testing is conducted using two specific sets of parameters for the specimens. By numerical resimulation and experimental results, the accuracy of the mathematical model is validated, and the role of the mass of circular isolators is also investigated. Moreover, the coupling effect on the proposed bidirectional mechanism is also proved to be negligible, which further significantly enhanced the feasibility of practical applications.
Keywords: isolation, nonlinearity, rolling, eccentricity, shaking table test, frictional damping |
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