Development and characterization of a gravity-well-based triple friction pendulum system

Abstract

Recently, variable stiffness double friction pendulum systems have been extensively studied. Nonetheless, achieving high initial stiffness, softening stiffness during Design Basis Earthquakes (DBE), and subsequent high stiffness during Maximum Considered Earthquakes (MCE) within the limited space of curved surfaces remains a significant challenge. To address this issue, a novel gravity-well-based triple friction pendulum system (GW-TFPS) with adaptable stiffness is proposed. The upper and lower sliding surfaces feature interior spherical geometries with a small radius to enhance self-centering capability, while the exterior surfaces are shaped according to a logarithmic function to ensure reduced stiffness. Additionally, the internal sliding surfaces are spherical with an even smaller radius, ensuring higher stiffness. The friction coefficient of the internal sliding surfaces is larger than that of the top and bottom surfaces to ensure they engage last. The design theory, working mechanism, and restoring force model of GW-TFPS were presented at first. A specimen was fabricated and tested under various vertical pressures to evaluate its characteristics, which were compared with a gravity-well-based double friction pendulum system (GW-DFPS) of identical dimensions. The GW-TFPS not only maintains the superior self-centering and energy dissipation capabilities of the GW-DFPS at small displacements but also exhibits high stiffness at larger displacements, significantly enhancing the system's displacement-limiting capabilities.