Evaluation of Seismic Response Parameters of Steel Buildings subjected to Multiple Earthquakes

In regions with high level of seismicity, structures may be not only influenced by main strong ground shocks but, also would be subjected to series of powerful aftershocks. For example, after the 2010 Chile earthquake with the moment magnitude (MW) of almost 8.8, about 21 aftershocks tremors with moment magnitude more than 6.0 happened during a period of two months. Because of the short time intervals between the main ground shock and following probable aftershocks, generally there is not enough time to rep air the damages. Yet, powerful aftershocks are able to create larger lateral displacement and higher residual displacement demands compared to those of a single mainshock. There are several researchers who were investigated the effects of aftershocks on the structures, but most of them applied the modeling of structures as a single degree of freedom (SDOF) or at most, two-dimensional multi-degrees of freedom oscillators for conceptual simplicity. In the present research, nonlinear response parameters of three-dimensional steel buildings subjected to an ensemble of three-component earthquake records are studied. Three twenty-story steel rigid frame skeletons with full symmetricity in height and plan of the structural resistant system were exposed to a set of six multiple earthquake records. Moreover, the parameters selected as representative of structural behavior include maximum interstory drift, residual interstory drift and shear lag effect. The results of this research revealed that the variations in response parameters of the studied models depend on the distinct spectral factors such as the frequency content of mainshock and aftershock tremors, the scale factor of mainshock record, the aftershock intensity and the number of stories as well as the fundamental period of the structure.