Experimental Investigation of Wear Effects on the Friction Coefficient of a Curved Surface Slider: Comparison of Small- and Full-Scale Tests

The current practice to determine friction properties of sliding isolation systems is to perform displacement-controlled dynamic tests where the effects of several loading conditions with different amplitudes, loading velocities, and vertical forces are of concern. The number of cycles in these tests is generally three for most of the loading conditions assumed to be representative of seismic conditions. On the other hand, the isolator may undergo small-amplitude but large-cycles of service motions due to thermal deformations and accidental loads. In that case, the methodology requires to perform cyclic tests on small-scale samples of the slider material (not the isolator) considering very large accumulated sliding distances such as 1000 m for use in buildings, and 10,000 m for use in bridges. However, two unsettled issues are regarded: (i) the suitability of small-scale slider tests to estimate the characteristics of full-scale sliding isolation systems and (ii) the change in seismic performance of a sliding isolation system after it is subjected to a large amount of accumulated sliding distance. In the present study, both a full-scale double concave friction pendulum (DCFP) and small-scale sample composed of the slider of the DCFP are subjected to a total accumulated sliding distance of 1000 m. The corresponding variations in friction properties are comparatively presented, demonstrating that small-scale test results provide reasonable estimates for the friction properties of the tested full-scale DCFP. Moreover, the seismic response of the investigated DCFP remains almost the same regardless of the considered sliding distance.