Behavior of Quintuple Friction Pendulum System Under Near-Fault Earthquakes

The Quintuple Friction Pendulum (QTFP) system is a new generation sliding isolation having six spherical sliding surfaces with five effective pendula. Due to multiple sliding surfaces, QTFP system shows highly adaptive behavior under different hazard level of earthquakes, despite being a passive system. The paper describes mathematical model and seismic response of QTFP system under 60 earthquake records consisting of service level, design basis and maximum considered earthquakes. To study the erect of directivity focusing and fling step, additional 15 records consist of far-field, near-fault with forward directivity and fling step erect are also considered. Three types of effective period and effective damping in combination with two different displacement capacities of QTFP bearing resulting in six isolator designs are considered. The seismic demand parameters like base shear, top floor absolute acceleration and isolator displacement have been studied. It is found that the QTFP bearing stir ens at low input, softens with increasing input, and then stiffens again at higher levels of input. Thus, it shows highly adaptive behavior under different hazard levels of earthquake. Further, due to forward and backward momentum conveyed by the directivity pulse, near-fault directivity effect imposes higher demand compared to fling step containing only forward momentum.