Fundamental Study on the Super-Long-Period Active Isolation System

Background: Since the Hanshin-Awaji Earthquake Disaster, the number of isolated structures has been greatly increased. The natural period of the isolation system is designed around $3s$⁠, because the predominate period of observed seismic waves is usually 0.1 to $1s$⁠. However, relatively long period seismic waves have been observed in various earthquakes, and the resonances of long-period structures, such as high-rise buildings, during earthquakes have been reported at the same time. Therefore the natural period needs to be extended. When extending the natural period of the isolated structure using rubber bearings, its stiffness needs to be reduced. It is more difficult to extend the natural period of the isolation system than the conventional system because of a buckling problem. Therefore we propose a super-long-period active seismic isolation system as a new method for extending the natural period of the isolated structure. This system consists of rubber bearings and hydraulic actuators. Method of approach: In this study, we designed a control system by using the model matching method. This is one of the classical control system design methods. Additionally we applied a genetic algorithm (GA) to select parameters of a transfer function. Results: The system designed by applying the GA could reduce response acceleration sufficiently compared with the input acceleration. Further waveforms of the response acceleration retain almost straight forwardly, so this indicates good performance of isolation. Therefore, application of super-long-period active isolation is an effective technique to improve the performance of isolation. However, the control forces are big, and the system needs $95.5×106N$ for the El Centro NS wave as control force. This force is equivalent to 21 actuators that are used in a large shake table, so there are few possibilities to realize active isolation. Conclusion: The required control force of hydraulic actuators is big, although the super-long-period active isolation system possesses good performance of isolation compared with the conventional isolation system. Therefore it is difficult to apply this isolation system to the real structure. However, the problem regarding requirements of the actuator should be solved because of the realization of an active seismic isolation system. Therefore, we will examine for the parameters of the system and semi-active isolation system.