Frictional Response of PTFE Sliding Bearings at High Frequencies

Dynamic tests were done on polytetrafluoroethylene (PTFE) sliding bridge bearings to evaluate their frictional characteristics at frequencies above 1 Hz. High frequency seismic responses of PTFE bearings are expected to occur in bridge structures in eastern North America, where the estimated ground motion is well above 1 Hz. Three different PTFE-steel interfaces were tested at frequencies ranging from 0.02 Hz to 5 Hz, with displacement amplitudes of up to 70 mm and under confining pressures ranging from 5 MPa to 45 MPa. The experimental results showed a significant initial transient frictional response at frequencies above 1 Hz before the dynamic, steady-state, frictional behavior was achieved. This transient response is characterized by an initial high static coefficient of friction that slowly decreases to a dynamic steady-state coefficient of friction after several response cycles. Modifications to an existing mathematical friction model are proposed to take into account this initial transient frictional response.