One of the main issues related to the design of sliding isolation bearings, like Curved Surface Sliding (CSS) isolators, subjected to large ground motions, generated e.g. at near-fault locations, concerns the choice of the optimal value of the coefficient of friction at the sliding interface.  High friction values (on the order of 10% and more) are recommended to provide effective dissipation of the seismic energy and control the displacement of the isolated structure, but large friction forces associated to high velocities produce huge heat generation at the sliding interface and following increase in temperature, which affects the properties of the friction materials. When the temperature approaches the melting temperature of the liner, which is usually made of a thermoplastic material, a decrease in friction coefficient and wear resistance is typically observed, while the material becomes softer and reduces its load-carrying capacity.

In the present study the reliability of composite materials consisting of a base polymer with fillers to enhance the thermal conductibility for employment in sliding isolation bearings with high dissipation capability has been investigated.

In the first part of the investigation, different composite materials were evaluated in small scale tests and the sliding coefficient of friction was determined at velocities from 100 to 400 mm/s.  After this screening, a composite material with coefficient of friction larger than 10 percent (hereinafter called HD-Composite) was chosen.  Further tests were then performed to assess the dependence of friction on ambient temperature and contact stress.

Validation tests were performed on prototypes of CSS isolators equipped either with the HD-Composite, or with current sliding materials, including pure PTFE, PTFE-based composites and other thermoplastic materials.  Each isolator was subjected to the application of multiple cycles of horizontal displacement of 400 mm amplitude at several velocities up to 400 mm/s.  Differently from the CSS units equipped with current materials, the isolator with the HD Composite showed a good stability of its dynamic properties (lateral stiffness and equivalent damping) over 20 cycles of excitation, with changes less than 20% with respect to the values measured at the third cycle.  In addition, an increase in the load-carrying capability of the H-D Composite was attained by the particular fillers, and even though large temperatures (above 175°C) were measured at the sliding interface, the slider proved to be able to sustain 20 cycles of displacement at 400 mm/s without failure.