Research and Development of Intelligent Seismic Isolation System Using Air Bearing

Abstract

This study aims at research and development of the intelligent seismic isolation system using air bearings as isolation device and Earthquake Early Warning (EEW) as trigger of isolation system. In October 2007, EEW was started providing to resident of Japan. The EEW system expects earthquake intensity and arrival time at particular place by analysis of seismic wave that was observed near the earthquake center. Therefore social and technical application of the system is strongly expected for suppression of disaster scale. On the other hand, long period seismic waves having predominant period of from a few seconds to a few ten seconds have recently been observed in various earthquakes. Also resonances of high-rise buildings and sloshing of petroleum tanks in consequence of long period seismic waves have been reported. In metropolises of Japan such as Tokyo, Osaka and Nagoya, it is expected that long period seismic waves are excited in large earthquakes because these are located on sedimentary layers. Therefore the isolation system having very long natural period or no natural period is required. In this study, we propose an isolation system having no natural period by using air bearing as isolation device. Air bearing is a bearing that can reduce contact friction between floor and the bearing by thin air film produced by compressed air. In general, the air bearing is used as heavy machinery moving equipment. The approximate friction coefficient is 0.0005 to 0.001, so that the system using air bearing almost isolates seismic wave. In addition, the EEW is applied as trigger of isolation. The EEW is applied for turning gas and electrical heater off, too. P-wave sensor is also equipped and it can operate as trigger in case of near-field earthquake or when EEW system could not work properly. Furthermore, steel plate equipped at the bottom of the air bearing can operate as friction bearing when air bearing does not work. In this paper, we describe results of earthquake response analysis of the intelligent isolation system using air bearing. From results of the analysis, it was confirmed that response acceleration depends on friction coefficient only, and the system has good isolation performance not only against typical seismic wave, such as El Centro wave, but also against long period seismic wave. However residual displacement remains after seismic input stopped. Additionally, experimental test was executed so as to investigate basic performance of isolation. As a result, it was confirmed that the isolation system has good isolation performance.