Evaluating the Performance of a Nonlinear Dual-Mode Vibration Isolator/Absorber System

Abstract

During the event of an earthquake, motion-sensitive equipment inside a building can be protected from seismic disturbance using a floor isolation system (FIS). Its behaviour is assumed linear when it displaces within the allowable capacity of its seismic gap and nonlinear when it displaces beyond, resulting in an impact between the FIS and the displacement limit, which can be augmented with a shock absorber. This induced nonlinearity may create a non-negligible dynamic coupling between the primary structure (PS) and the FIS, which can possibly be tuned to reduce the PS responses during strong earthquakes. This research aims to evaluate the performance of the FIS as a vibration isolator when subjected to low-intensity earthquakes (i.e., before impact occurs) and as a vibration absorber when subjected to high-intensity earthquakes (i.e., after impact occurs). Such a FIS is termed "dual-mode vibration isolator/absorber system" whose quantities of interest concern peak FIS acceleration and peak PS interstory drift when evaluating the isolation performance and the absorption performance, respectively. Two approaches are used to realize and evaluate the FIS’s dual behaviour. A probabilistic approach is based on a numerical simulation that uses a nonlinear reduced order model to investigate the FIS performance when subjected to a suite of synthetic ground motions at various hazard levels, as well as to optimize some controlling parameters via two competing objective functions. An experimental approach is based on a lab-scale experiment to study the FIS performance when attached to the second story of the PS that is subjected to four historic ground motions. The data has shown promising result that suggests the dual performance of the FIS.