Development of adaptive base isolation systems for seismic response control of structures

Seismic isolation systems have been implemented as an earthquake protection system in several critical structures, such as hospitals, emergency response centers, and bridges. By incorporating a base isolation system between the foundation and the basemat of a building, the superstructure can be isolated from the ground shaking. As a result, the energy transmitted from the ground to the structure is limited and, thus, the response of the superstructure is reduced. Such response reduction, however, is achieved at the expense of a large deformation at the isolation level. In particular, when an isolated structure is subjected to large amplitude, long-period, pulse-type ground motions, the deformation at the isolation level may be unacceptably large. To avoid such problems, supplemental damping devices are often incorporated within the isolation system. Although utilizing supplemental damping devices at the isolation level can effectively reduce the deformation of the isolation bearings, the beneficial effect of isolation may be decreased when the building is subjected to more frequent small-to-moderate earthquakes. As an alternative, adaptive supplemental damping devices may be implemented to improve the performance of an isolated structure when subjected to disparate earthquake ground motions.; For this research project, the effectiveness of adaptive base isolation systems is investigated for seismic protection of buildings. The seismic response of a scale-model, base-isolated, three-story structure is investigated both experimentally and analytically. Two types of base isolation bearings are utilized within the isolation system: Friction Pendulum System (FPS) bearings and Low-Damping Rubber (LDR) bearings. Adaptive supplemental dampers are incorporated within the isolation system to provide damping capacity that can be modulated in real-time based on an H_∞ feedback control algorithm. The adaptive supplemental dampers utilized herein are variable fluid dampers in which the damping capacity is modulated via an electromechanical control valve. Both numerical simulations and experimental testing are performed using a variety of earthquake ground motions. The results demonstrate that, for various types of ground motions, the use of variable dampers not only reduces the response of the structure but also maintains the deformation of the isolation bearings within a prescribed allowable limit.