Modeling and experimental validation of a novel hydraulic inertia-type vertical isolation system

Vertical isolation technologies struggle to meet the demands for static support rigidity and dynamic isolation flexibility simultaneously. To resolve this problem, the present study designed a hydraulic inertia-type vertical isolation system (HIVIS) to protect equipment against seismic effects. This HIVIS contains a counterweight that enhances the system's static rigidity, while simultaneously increasing its dynamic flexibility through the counterweight's inertial force. Energy dissipation occurs through the viscous flow within a hydraulic link connecting the counterweight to the isolated equipment, which effectively mitigates the equipment's acceleration and displacement responses. A mathematical model of the HIVIS was constructed, following which a dimensionless equation of motion was derived. For experimental validation, a component test was conducted on a prototype HIVIS to determine the nonlinear characteristics of the hydraulic link, including its frictional force and damping coefficient. Subsequently, the prototype HIVIS was tested on a shaking table using vertical sine-sweep and various earthquake excitations. The experimental results aligned well with the theoretical predictions, confirming the constructed model's accuracy in simulating the dynamic behavior of the HIVIS. The experimental results also indicated that the HIVIS reduced isolation displacement by approximately 50 % compared with a traditional vertical isolation system (VIS) while consistently maintaining high isolation efficiency. Furthermore, the HIVIS exhibited excellent antiresonance performance under long-period near-fault ground motions. In summary, the analytical and experimental findings of this study indicate that HIVISs overcome the design limitations of traditional VISs and provide a more robust and comprehensive protection mechanism for precision equipment subjected to vertical seismic excitations.