Effect of Bidirectional Ground Motion on the Response of Double Concave Friction Pendulum Systems

Recent destructions of structures due to insufficient isolator deformation capacity have led to demands for greater seismic redundancy in seismic isolation design. For a friction pendulum system (FPS), the effect of bidirectional behavior of earthquakes on the maximum response and its effect on friction heating, temperature, and in turn on the maximum response can be significant. However, the extent of these effects under different FPS design parameters and different types of ground motions (GMs) is still not clear. In this study, an analytical model of double concave FPS considering the coupling effect of friction heating and bidirectional behavior was proposed and validated by bidirectional earthquake response orbits, which reflect the characteristics of both GMs and FPSs. Then, the effects of bidirectional GM and corresponding bidirectional temperature change on the response were investigated under different types of strong GMs. Finally, a performance-based design method with a bidirectional-effect-compensation mechanism was proposed. For double concave friction pendulum bearings with PTFE-related layers, it was found that the bidirectional behavior of earthquakes will amplify the maximum isolator displacement by an average of 110-210% (60 MPa) and the maximum superstructure acceleration by an average of 100-140% (60 MPa) under strong GMs (PGV-C1 > 0.2 m/s) and optimum design parameters. The amplification ratio is not only influenced by GM characteristics but also highly related to the design parameters and friction-heating effect of DCFPS.