Experimental assessment of sliding materials for seismic isolation systems

Abstract

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\ud 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.\ud 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 North American specifications and the relevant dynamic properties assessed from the Horizontal Load—Displacement loops. The experimental outcomes confirmed\ud that the frictional characteristics provided by the proposed procedure can be reliably used in the design of seismically isolated structure

Experimental investigation of the re-centring capability of curved surface sliders

“…L‐TF and L‐CM pads were used in the DCSS bearings, whereas NL‐CM pads in the SCSS bearings. The coefficient of friction of the three materials was characterized in small‐scale tests conducted at the laboratory of Politecnico di Milano in accordance with the experimental procedure described elsewhere . The material specimens were tested under the application of a constant pressure of either 7.10 MPa (L‐TF and L‐CM materials) or 3.98 MPa (NL‐CM material), corresponding to the actual load acting on the pads when installed the CSS bearings due to the weight of the mock‐up.…”

“…The criterion was indeed formulated under the assumption that the mechanical properties of the isolation system, lumped in the parameter d 0 in Equation , are constant. This is in general not true for the CSS, as the coefficient of friction is noted to be dependent on a number of factors among which there are the axial load, the velocity of sliding and the temperature . Research addressing the re‐centring capability of CSSs is very recent, and definite results have not yet been achieved.…”

Sliding implant‐magnetic bearing for adaptive seismic mitigation of base‐isolated structures

“…Although they introduce a restoring force into the sliding system, the design of the frictional coefficients and stiffness of the restoring device both have an essential impact on the isolation performance. In this case, a number of self‐lubricant materials such as polytetrafluoroethylene (PTFE), ultrahigh molecular weight polyethylene, polyformaldehyde (POM), and other thermoplastics have been proposed for facilitating the workability of sliding surface . However, the choice of materials is significant because the tribological behavior varies from material to material.…”

“…In this case, a number of selflubricant materials such as polytetrafluoroethylene (PTFE), ultrahigh molecular weight polyethylene, polyformaldehyde (POM), and other thermoplastics have been proposed for facilitating the workability of sliding surface. [17][18][19] However, the choice of materials is significant because the tribological behavior varies from material to material. Moreover, the sliding condition of the bearing matters as well, for example, the coefficient of friction reduces after three cycles of loading at high velocities 20,21 ; abnormal sliding behavior like stick-slip influences the characterization of friction behavior.…”

Formulation of a Novel Opensees Element for FPS Bearings With Enhanced Friction Model

“…Filled PTFE [6][7], Ultra High Molecular Weight (UHMWPE) [8], and Polyamide (PA) [9] have been used in applications as lining materials of the slider. The coefficient of friction of thermoplastic materials changes with a number of factors including the applied pressure and the velocity of sliding, the temperature, the roughness of the mating surface, and the wear and contamination of the sliding surfaces [10][11][12][13][14][15]. The typical dependency of the coefficient of friction on velocity and pressure is illustrated in Figure 2.…”