Multiple Yield and Bounding Surfaces Model for Analysis of Multiple Friction Pendulum System

In order to systematically investigate the mechanical characteristic of a multiple friction pendulum system with more than two concave sliding interfaces and one articulated slider located between these concave sliding interfaces, on the basis of the plasticity theory, a plasticity model called the multiple yield and bounding surfaces model is proposed in addition to analytical formulations derived from the proposed concept of subsystems in this study. The proposed model has two separate groups of multiple yield and bounding surfaces. The first group is adopted to describe the mechanical behavior of the subsystem including the concave sliding interfaces above the articulated slider and the second group is used for modeling the sliding characteristic of the subsystem representing the concave sliding interfaces below the articulated slider. The connection of these two subsystems in series forms the mechanical characteristic of the entire MFPS isolation system. By virtue of the proposed model, the phenomena of the sliding motions of the MFPS isolator with multiple concave sliding interfaces under cyclical loadings can be clearly understood. Analytical results infer that the natural frequency and damping effect of the MFPS isolator with multiple concave sliding interfaces change continually during earthquakes and are controllable through appropriate designs.