Effects of Aftershocks on the Seismic Performances of Reinforced Concrete Eccentric Frame Structures

Strong aftershocks have the potential to cause accumulated damage in structures, a feature which has been reported in post-earthquake reconnaissance studies, particularly for eccentric or irregular structures. This study aims to investigate the seismic behaviors of eccentric RC structural models under mainshock–aftershock (MSAS) sequences. In this study, three-dimensional structural models with eccentricities of 5%, 10%, 15%, 20%, 25%, and 30%, and an eccentricity of 0 (symmetric structural model) are developed by changing the positions of the centers of the structural mass. A static pushover analysis and a nonlinear time history analysis are conducted on the structural models with different eccentricities considering unidirectional and bidirectional earthquake loading (including mainshock ground motion and MSAS sequences). The amplitude of the aftershock ground motion is scaled according to the structural damage levels calibrated with the inter-story drift ratio (IDR). Furthermore, the differences in seismic responses between the unidirectional and bidirectional eccentric structures are discussed. The results show that the peak displacements of the unidirectional eccentric structures under MSAS sequences are nearly 1.4 times higher than those under mainshock ground motions. The structural seismic responses under unidirectional earthquake loading are more sensitive to the intensity of aftershock ground motions than those under bidirectional earthquake loading. Compared with unidirectional eccentric structures, bidirectional eccentric structures are more sensitive to the intensity of aftershock ground motions and have larger torsional angles and more complex displacement trends. The maximum displacement and the maximum IDR of bidirectional eccentric structures under MSAS sequences can reach 1.5 times and 1.4 times of those under mainshock ground motions, respectively.