Inelastic seismic behavior of asymmetric structures with mass and stiffness eccentricity under bidirectional ground motions

Abstract

Structures with an asymmetric plan have proved to be severely vulnerable during the past earthquakes. The vulnerability may arise due to the uneven distribution of stiffness or mass. Most of the research focused on studying the eccentricity arising due to the irregular stiffness distribution. On the other hand, the systems with mass eccentricity arising due to the uneven distribution of mass at floor level are given relatively little attention. Hence, the present paper comprehensively studied the stiffness and mass eccentric systems together. In each case, the structure is subjected to bidirectional components of ground motion, which reflects the real situation more closely. So, for the lateral load-resisting elements (columns), effect of biaxial interaction due to simultaneous bidirectional movement is included in the hysteresis behavior as explained in the paper to make a reasonably accurate prediction. Primarily idealized single-story systems were used to study how asymmetric structures are vulnerable if they have stiffness or mass eccentricity. Further, the three-story asymmetric systems were also included in the scope of the study to observe the effect of higher modes. To simulate a more practical situation, the present paper considers higher eccentricity in the first story of the three-story system due to functional reasons, while the upper stories have lesser eccentricities compared to the first story.The present study shows that mass eccentric systems are equally vulnerable to earthquakes as stiffness eccentric systems. Further, three-story systems show a manifold increase in response compared to its single-story counterparts. Such a study may help to develop more insight into the generic behavior of plan asymmetric systems, leading to the improvement of design guidelines.