Analysis and validation of theoretical equations for a seismic isolation system with a multi-level friction damper

Traditional seismic isolation structures perform poorly due to the impact of velocity pulses from near-field seismic waves. A conical friction pendulum isolator (CFPI) is a variable-curvature seismic isolation system, which can mitigate the resonance effect produced in seismic isolation structures by the velocity pulses of long-period near-field seismic waves. A multi-level friction damper (MFD) has a multistage energy dissipation mechanism and has been proven to have excellent shock absorption effects in structures for earthquakes of different intensities. Therefore, the present study integrated an MFD into a CFPI to develop a seismic isolation system (CFPI + MFD system) with improved safety under near-field seismic waves. Theoretical equations were established for this system to enable numerical simulation analysis. According to the results of numerical simulation analysis, the designed CFPI + MFD system has an excellent seismic isolation effect, whether under near-field seismic waves or large earthquakes. To verify the accuracy of the numerical simulation results, this study performed a shaking table test for a single-degree-of-freedom (SDOF) structure with the designed seismic isolation system. Experimental data derived from the shaking table test and the results of numerical simulation analysis were used to conduct fitting of the superstructure acceleration, base sliding displacement, and hysteresis loop data. The fitting results indicated that the numerical and experimental superstructure acceleration, base sliding displacement, and hysteresis loops exhibited a good fit, which validated the accuracy of the theoretical equations formulated in this study.