Numerical Development and Assessment of 3D Quintuple Friction Pendulum Isolator Element Based on Its Analytical and Mathematical Models

Abstract

ABSTRACT This paper aims to develop, assess, and numerically implement analytical models for the newly introduced Quintuple Friction Pendulum Isolator (QFPI) which can identically capture its real experimental performance and also have the ability to capture the bi-directional, tri-directional, and vertical-horizontal coupling behavior of it, raising the predictive capability of nonlinear response history analyses and also lowering computational and experimental complexity and cost. The mathematical formulation proposed in this paper aims at addressing the variability of the coefficient of friction based on experimentally obtained data from prototype test on QFPI system. The formulation accounts for variation in the coefficient of friction with the instantaneous change of axial load and sliding velocity at the isolator contact interfaces. Furthermore, it considers the experimentally discovered phenomena such as the static frictions developed at the very first initiation of motion, breakaway, or at motion reversals, stick-slip. The proposed model has been coded three-dimensionally by a series model in the object-oriented finite element software OpenSees based on its mathematical formulations. The primary assumptions in developing the friction models and corresponding parameters are validated by available experimental data and suggestions. A case study has been considered to validate the developed element and also to investigate and demonstrate the prediction capability of it when applied to real situations, such as variations have been made in displacement, base shear, and acceleration demand for this system under dynamic behavior of earthquakes. Moreover, the effects of vertical-horizontal coupling behavior of QFP isolated system on its horizontal responses have been investigated numerically and justified analytically under the existence of vertical acceleration, by subjecting the system to a variety of X and XY (horizontal only) and 3D (horizontal plus vertical) input excitations for comparison.