Comparison of the performance of frictional pendulum isolators and suspended pendulum isolators

Earthquakes, as a major cause of excitation and damage to structures, have always posed one of the most significant challenges in structural design. Consequently, various methods have been proposed to mitigate the impact of seismic events. Seismic isolators, as a subset of structural control methods, represent an effective solution by being placed between the superstructure and substructure to alter the input vibrations from destructive to non-destructive. Among the various types of seismic isolators, frictional pendulum isolators are widely used, while suspended pendulum isolators, a more recent development by the authors, offer an alternative approach. This paper presents a comparison of the two types of isolators, evaluating their performance, benefits, and limitations under different seismic conditions. Challenges associated with frictional pendulum isolators, such as the existence of a non-periodic region near the center, permanent displacements, and the inability to effectively isolate seismic forces under low acceleration loads, are examined. In this research, a friction pendulum seismic isolator with different friction coefficients and a suspended pendulum seismic isolator with different damping have been modeled and investigated. The models have been subjected to several seismic loadings, and the system response has been obtained. Fast Fourier transform analysis has been performed on the results. It is demonstrated that these issues can lead to fatigue and damage to non-structural components under cyclic loading. Furthermore, the study highlights that frictional pendulum isolators may not adequately isolate seismic loads with low acceleration, which can negatively affect the overall performance of seismic isolation systems. Cyclic loading results showed that the efficiency of the friction pendulum isolator in terms of energy dissipation is very low compared to the suspended pendulum isolator, and the resonance in the friction pendulum isolator is not fully controlled.