Seismic Response of Triple Friction Pendulum Bearing under Near-Fault Ground Motions

Abstract

The seismic response of a stiff single-story and a flexible multi-story building isolated with triple friction pendulum bearing (TFPB) are investigated under the pulse-like (near-fault, NF-Pulse) and (NF-No Pulse) NF nonpulse ground motions. By varying the geometric parameters, such as the effective spherical surface radius, or by specifying different friction coefficients for each surface, one can adjust the behavior of the bearing. Consequently, the stiffness and damping ratio of the system can be optimized for multiple performance objectives under multiple levels of hazard. The seismic responses are evaluated under different isolation parameters for the displacement of isolation and the superstructure demand functions of the system, including the base shear, maximum inter-story drift and top floor absolute acceleration of the isolated structure. First, the seismic response of twenty TFPBs with different stiffnesses and damping ratios are investigated under NF motions. A comparison of results suggested that the displacement of the TFPB under the NF-Pulse motion is about twice that of the NF-No Pulse motions. The best performance of the system is found when the TFPB works in its third stage of motion. Next, from the sensitivity analysis, the effect of each parameter of the TFPB on the seismic response of system is investigated and the trends for optimal parameters of TFPB are presented. The criterion selected for optimality is to minimize the performance function that considers all seismic responses simultaneously. The optimum ranges for the related parameters are: (a) 0.02–0.04 for the coefficient of friction of the inner surface; (b) 0.06–0.14 and 0.04–0.12 for the bottom concave plate under the NF-Pulse and NF-No Pulse, respectively; (c) 0.06–0.18 and 0.06–0.16 for the top concave plate under the NF-Pulse and NF-No Pulse, respectively; (d) 200–500 mm for the radius of curvature of the inner surface; and (e) 2500–4500 mm for the outer surface.