## 3 Results and Discussion
### Seismic Dynamic Analyses of Unidirectional Eccentric Structures
#### 3.2.1 Response of the Unidirectional Eccentric Structure under Unidirectional Mainshock
Among them, the displacement of the aftershock is, at most, 12% larger than that of the mainshock. This reflects that after experiencing a mainshock of 0.25 g, structures may suffer aggravated damage when loaded with aftershocks again of the same intensity. However, compared with structures experiencing a mainshock of small magnitude (i.e., 0.15 g), in the case of a mainshock of large magnitude, the influence of aftershocks on the structural model is significantly reduced. Figure 14d presents that with an increase in eccentricity, the IDR grows obviously, and the growth rate slows down slightly at high eccentricity; structures with an eccentricity from 0% to 15% are more sensitive to the effects of aftershock than structures with higher eccentricity. When the scaling factor is less than 0.9, the maximum IDR of all structures during a scaled aftershock do not exceed that during the mainshock. However, when the scaling factor of aftershock amplitude is 1, the maximum IDR response in an aftershock is equal to 1.15 times that in the mainshock. Compared with the case of the structural model experiencing mainshock PGA = 0.15 g, the IDR responses in an aftershock can reach 1.5 times of that in the mainshock, when the mainshock PGA is 0.25 g. The results illustrate that the influence of aftershocks on the structural model is not as great as that of the former case, and it has little influence on the growth factor of IDR in aftershocks. When the mainshock PGA is 0.32 g, the structural model's displacement rises as the eccentricity increases, but it does not change significantly as the aftershock amplitude changes when the eccentricity is the same. In Figure 14e, the aftershock displacement increases by less than 5%. The reason is as follows: When the structure is about to collapse, the prior damage caused by the mainshock to the structural model is so large that the effect of aftershock is negligible, which causes the displacement following the aftershock to possibly be less than the displacement after the mainshock. For the maximum IDR, it similarly shows that the aftershock has little effect. As shown in Figure 14f, the response of structural models of eccentricity 0-25% also has an upward trend, with the increase in eccentricity under the mainshock PGA being 0.32 g. However, the scaled aftershocks do not aggravate the structural damage directed by the index of maximum IDR. After loading the aftershock with the same intensity as the mainshock (0.32 g), the maximum IDR of the structure may not increase. The reason is that the structure already has experienced a large response under the mainshock, and even become severely damaged. Although the effect of scaled aftershocks does exist, it is still difficult to surpass the effect of the mainshock. To sum up, with an increase in the mainshock PGA, the influence of aftershocks on the top floor maximum displacement and the maximum IDR of structures tend to decrease gradually. Compared with other mainshock PGAs, the effect of aftershock is most evident when the mainshock PGA is 0.15 g. The aftershock displacement of the structure reaches 1.4 times the mainshock displacement and the IDR reaches 1.5 times the mainshock displacement. When the mainshock PGA is 0.32 g, the response of the structure under the aftershock does not exceed the maximum response of the mainshock since the structure under the mainshock is close to destruction or even collapse.