Characterizing friction in sliding isolation bearings

Abstract

The force-displacement behavior of the Friction Pendulum ™ (FP) bearing is a function of the coefficient of sliding friction, axial load on the bearing and effective radius of the sliding surface. The coefficient of friction varies during the course of an earthquake with sliding velocity, axial pressure and temperature at the sliding surface. The velocity and axial pressure on the bearing depend on the response of the superstructure to the earthquake shaking. The temperature at an instant in time during earthquake shaking is a function of the histories of the coefficient of friction, sliding velocity and axial pressure, and the travel path of the slider on the sliding surface. A unified framework accommodating the complex interdependence of the coefficient of friction, sliding velocity, axial pressure and temperature is presented for implementation in nonlinear response-history analysis. Expressions to define the relationship between the coefficient of friction and sliding velocity, axial pressure, and temperature are proposed, based on available experimental data. Response-history analyses are performed on FP bearings with a range of geometrical and liner mechanical properties and static axial pressure. Friction is described using five different models that consider the dependence of the coefficient of friction on axial pressure, sliding velocity and temperature. Frictional heating is the most important factor that influences the maximum displacement of the isolation system and floor spectral demands if the static axial pressure is high. Isolation system displacements are not significantly affected by considerations of the influence of axial pressure and velocity on the coefficient of friction.

Finite Element Modeling of Single and Multi-Spherical Friction Pendulum Bearings

“…Regarding the friction which is the most important characteristic for the operation of the FP bearing, rigid contact is used to model the interfaces between the isolators' parts. In literature [17] it has been thoroughly investigated the influence of the friction models adopted for the analyses. Comparing Coulomb friction model with other more sophisticated which took into account the sliding velocity [6], the pressure or the temperature, have been concluded that the Coulomb friction is adequate to simulate the friction of the sliding surfaces of a FP bearing.…”

Numerical Assessment of Concave Sliding Isolator’s Mechanical Behavior Under Bi-Directional Motion

“…More specifically, a plethora of studies have been presented in the literature addressing the dependence of the friction coefficient upon contact pressure, sliding velocity and repetition of cycles that induces temperature rise at the sliding interfaces, see e.g. [3,5,9,10,11,13,14,17] just to quote a few. The common backbone of these studies is to alert the structural designer against oversimplification of the FPS behavior at the modeling stage.…”

Comparison of Friction Models for the Curved Surface Sliding System in the Nonlinear Seismic Analysis of Base-Isolated Buildings

“…In particular, experimental results indicate that the dynamic-slow friction coefficient can be assumed 2.5 times lower than μfast [17], while parameter can be considered equal to approximately 0.1 s/mm [5].…”

“…BIA.MFT and BIB.MFT) friction properties by taking into account the dependence of the dynamic-fast friction coefficient on the heating at the sliding surface when the slider is in motion. To this end, a reduction factor kT of the friction coefficient [5] , 0.02…”

“…However, theoretical and experimental studies have uncovered the complex nonlinear behaviour of the CSS bearings, highlighting the presence of many parameters affecting their friction coefficient at the sliding surface. More specifically, the friction force changes with: (a) the sliding velocity, whose increasing values produce a friction coefficient which increases by an exponential law [2]; (b) the axial pressure, with a high-velocity (dynamic-fast) value of the friction coefficient significantly reducing with the axial pressure and a low-velocity (dynamic-low) value which is relatively unaffected [3,4]; (c) the temperature when the slider is in motion, influencing the friction coefficient which decreases rapidly as the temperature at the sliding interface increases from -40 °C to 20°C and trends to a constant value for temperatures greater than 250 °C [5]; (d) the stick-slip phases, producing a transition between static and kinetic friction coefficients, whose ratio varies between 1.5 and 4.5 depending on the friction material adopted to coat the slider [6]. On the other hand, the axial load changes continuously during an earthquake and high values of the sliding velocity are expected under the horizontal components of near-fault ground motions, thus inducing torsional effects and residual displacements of the CSS system [7][8][9].…”