Adaptive Passive Seismic Isolation System for Mitigating the Acceleration Response of Floor-Mounted Equipment

Abstract

Protecting critical equipment in seismically excited buildings is essential to ensure functionality after an earthquake. Individual equipment or equipment sets can be seismically isolated from the building motion. Special isolators can be employed to mitigate the most severe accelerations that occur in the horizontal direction of a building. This paper presents the results of an investigation of the performance of an uncoupled bidirectional isolation system for horizontal isolation using a novel adaptive restoring force (ARF) device. The device changes the structural response transmitted to floor-mounted equipment by filtering the most intense portions of input floor acceleration histories to minimize the acceleration of the equipment and the stress demands imposed by the supporting structures. The ARF device utilizes restoring and damping elements to generate restoring forces that vary nonlinearly with displacement, resulting in a force–displacement curve with varying slopes and loading and unloading paths. The force–displacement relationship of the ARF device is characterized by high stiffness at small and large displacements, and low stiffness in between. A small-scale prototype was constructed to validate the ARF concept, and its force–displacement properties were observed for cyclic loading. A numerical model was developed that accurately predicted the relationship between the device force and displacement. The system’s performance was evaluated through numerical analysis of equipment installed on different levels of multistory buildings subjected to measured floor accelerations. The results showed that the horizontal isolation system effectively limited the transmission of the floor accelerations to the equipment. Furthermore, the results showed that the isolation system transformed the seismic acceleration profile from a high-amplitude and -frequency signal to one with a low quasi-constant amplitude and low frequency, acting as a low-pass filter under the most intense time window of the floor acceleration. Protecting critical equipment can be a significant concern for those who manage or work in facilities vulnerable to earthquakes. This study presents a new technology for horizontal seismic isolation of equipment, the adaptive restoring force device, that effectively minimizes the damaging effects of earthquakes on floor-mounted equipment in multistory buildings. The ARF device protects equipment by filtering out the most intense and destructive vibrations accompanying earthquakes, thus reducing accelerations on the equipment and its supporting structures. It transforms high-amplitude and -frequency vibrations to lower, more-constant levels. Unique to the ARF device is its adaptability to work effectively on any floor of a building, even on rooftops, while allowing considerable relative movement between the equipment and the floor. The results of this study are promising—equipment experienced reduced and nearly constant low-frequency accelerations during simulated seismic events. Although further research is required to address more complex problems, such as building torsion and vertical seismic effects, preliminary findings suggest that the ARF device offers a practical solution for preserving vital floor-mounted equipment in multistory buildings in earthquake-prone regions. This device can prove invaluable as a tangible solution for businesses, industries, and hospitals dependent on critical equipment.