Seismic behavior of asymmetric structures supported on TCFP bearings subjected to simplified near-fault pulses

Abstract

In this paper the effects of mass eccentricity of superstructure as well as stiffness eccentricity of isolators on the amplification of seismic responses of base-isolated structures are investigated. Superstructures with 3, 6 and 9 stories and aspect ratios equal to 1, 2 and 3 are mounted on a Triple Concave Friction Pendulum (TCFP) bearing. Three-dimensional linear model of superstructure mounted on nonlinear isolators are subjected to simplified pulses including fling step and forward directivity while various pulse period (Tp) and Peak Ground Velocity (PGV) amounts are scrutinized. Maximum isolator displacement and base shear as well as peak superstructure acceleration and drift are selected as the main engineering demand parameters. The results indicate that the torsional intensification of different demand parameters caused by superstructure mass eccentricity is more significant than isolator stiffness eccentricity. The torsion due to mass eccentricity has intensified the base shear of asymmetric 6-story model 2.55 times comparing to symmetric one. In similar circumstances, the isolator displacement and roof acceleration are increased 1.49 and 2.16 times respectively in the presence of mass eccentricity. Furthermore, it is demonstrated that torsional effects of mass eccentricity can force the drift to reach the allowable limit of ASCE 7 standard in the presence of forward directivity pulses. This aspect should be noted in the design of base-isolated buildings.