Seismic Responses of Isolated Structures with Mass Asymmetry Mounted on TCFP Subjected to Near-Fault Ground Motions

Abstract

This study is devoted to investigate the effects of mass eccentricity on seismic responses of base-isolated structures subjected to near-field ground motions. Superstructures with 3, 6 and 9 stories with aspect ratios equal to 1, 2 and 3 have been idealized as steel special moment frames resting on a reasonable variety of triple concave friction pendulum bearings considering different period and damping ratios for the isolators. Three-dimensional linear superstructures mounted on nonlinear isolators have been subjected to three components of near-field ground motions. Under 25 near-field ground motions, effects of mass eccentricity on the main parameters of the systems have been studied. These parameters have been selected as the main engineering demands including maximum isolator displacement and base shear as well as peak superstructure acceleration. The results indicate that the mass eccentricities do not have a remarkable effect on isolator displacement. In contrary to displacement, torsional effect of mass eccentricity has raised the base shear up to 1.75 times in a three-story superstructure. Additionally, mass eccentricity can amplify the roof acceleration of a nine-story model approximately 3 times in comparison with a symmetric one. It is also concluded that eccentricity in the direction of the subjected earthquake has the most impact on the base shear, while the isolator displacement and roof acceleration are mostly influenced by the eccentricity perpendicular to the earthquake path.