Optimal dynamic performance of partially Base-Isolated structure under seismic Excitations: Harmonic, Earthquake, and random

Abstract

In the present paper, a structural system is introduced, in which instead of executing two commonly used methods of column installation, namely ground-fixing and ground-isolation, some of the columns of the structure are fixed to the ground, and the remaining ones are isolated from the ground by the seismic base isolator. The interaction of these two sections on each other is controlled by connection to a viscoelastic damper. The proposed system is called a partially base-isolated structure. The present work aims to find the optimal isolated mass ratio and the optimal parameters of connection under different excitations. Therefore, once the conformity of the performance of the partial isolation system with two commonly used structure control systems is validated, the fixed-points alignment method is defined in the optimization under harmonic excitation. By executing the optimization operation under near- and far-field earthquakes, the desired parameters and seismic responses are obtained. In the optimal design of this system, even the severely poor performance of the seismic base isolator in the near-field earthquake, which is big displacement and acceleration, is resolved. Finally, under white-noise random excitation, the root mean square of the responses of the structure's components is evaluated in terms of the isolated mass ratio. As indicated by the results, the desired performance of this novel structure can be obtained in the case of base isolation, merely for 10–30% of the total structure mass, selection of a non-dimensionalized frequency below 0.5, and damping coefficient less than 0.1 for the viscoelastic connection. Accordingly, the base isolation in>70% of the structure's total mass is avoided. Moreover, meeting the architectural considerations and eliminating the executive constraints such as a big separation gap would lead to reduced construction cost, yielding significant cost-effectiveness compared to the fully base-isolated structures.