Effectiveness in protecting rigid-block-like objects through horizontal and vertical seismic isolation

Abstract

In this paper, a double, horizontal and vertical base isolation, is considered for the protection of rigid-block-like objects against seismic excitation. The equations of motion, the uplift and impact conditions are obtained under the hypothesis that the block can undergo full-contact and rocking motions. It is assumed that the horizontal isolation device has a hysteretic behavior, described with the Bouc-Wen model, whereas the vertical isolation has a visco-elastic behavior, modeled through a Kelvin-Voight device. Three rigid-block-like objects, representing a caryatid, a server and hospital cabinets are considered. Moreover, as base excitation, three earthquake horizontal and vertical records are selected accounting for their spectral content and PGA. The results of the seismic analysis are arranged in rocking maps and a comparison among the systems with the horizontal and vertical isolation, with only the horizontal isolation, and with no isolation are performed to check the effectiveness of the proposed seismic protection. Results show that the coexistence of horizontal and vertical isolation in protection against seismic excitation is particularly effective under earthquakes with high vertical PGA and in objects with high slenderness and heaviness. Finally, an analysis that consists of exciting the system with horizontal and vertical one-sine, impulsive base accelerations is performed to build the overturning spectra. Also, in this case, the double, horizontal and vertical isolation has manifested better performances than the other analyzed systems.