Experimental assessment of sliding materials for seismic isolation systems

Novel self-lubricating materials are currently being proposed to be used in sliding isolation systems such as the curved surface sliding isolator system, or pendulum bearing system, for the protection of buildings and structures. The current codes for anti-seismic devices are focused on the evaluation of the performance of the whole isolation system; as a consequence, a reliable procedure for the pre-assessment of the material combinations of sliding interfaces is currently missing. Therefore in this paper, an experimental methodology is proposed for the characterization of self-lubricating materials through tests on small-scale specimens performed using customized equipment able to reproduce the operational conditions of real isolation systems as per contact pressure, sliding velocity, temperature and slide path. The testing sequence has been designed in order to evaluate the sliding properties of the material in terms of static and dynamic coefficient of friction and wear resistance. Examples are reported for the assessment of two self-lubricating materials with different sliding characteristics. In order to validate the method and to confirm the reliability of extrapolating the results to real working conditions, prototypes of pendulum isolation systems incorporating the assessed materials have been tested according to the AASHTO (Guide specifications for seismic isolation design, 2nd edn. American Association of State Highway and Transportation Officials, Washington, DC, 1999) specifications and the relevant dynamic properties assessed from the Horizontal Load-Displacement loops. The experimental outcomes confirmed that the frictional characteristics provided by the proposed procedure can be reliably used in the design of seismically isolated structures.