Numerical modelling of heating effects in curved surface sliding isolators

The Curved Surface Slider, also known as the Friction Pendulum System, has become in the last years a very popular antiseismic hardware for base isolation of buildings and structures. A potential issue for sliding isolation systems is the degradation of the coefficient of friction caused by the temperature growth within the bearing due to the dissipation of the seismic energy as frictional heat. Both experimental and numerical investigations have pointed to the importance of the issue, and models accounting for the temperature dependence of the coefficient of friction at the material level have been recently proposed, which can be used in finite element analyses of the whole isolator. In this study, a three-dimensional finite element model of a Curved Surface Slider unit developed by the Authors is used to investigate in detail the influence of the path of motion on the temperature growth. In the first part, the finite element formulation and its validation are presented. The generation of frictional heat is reproduced in the model by locating a heat source on the surface of the sliding pad, with intensity of the heat flux depending on the coefficient of friction, the axial pressure, and the velocity. The coefficient of friction at the material level is routinely adjusted by the software at each calculation step on the current levels of pressure, velocity and temperature. In the second part, either unidirectional and multidirectional displacement-controlled orbits are challenged in finite element thermal-mechanical analyses in order to investigate the temperature growth inside the bearing and the relevant changes in the mechanical response of the device. The result point to the unsuitability of the unidirectional trajectories performed in the tests prescribed in current standards to reproduce the temperature rises that may possibly occur within the Curved Surface Slider unit under more general multidirectional orbits typical of real earthquakes.