## 3 Results and Discussion
### Seismic Dynamic Analyses of Unidirectional Eccentric Structures
#### 3.2.1 Response of the Unidirectional Eccentric Structure under Unidirectional Mainshock  
In order to find the structural seismic response parameters that are most sensitive to structure eccentricity, a dynamic time history analysis of unidirectional eccentricity under the ground motion records of the mainshock (Case UUM) was carried out. Taking the ChiChi-CHY029-N earthquake record as an example, the acceleration time history of the mainshock record is shown in Figure 7. The amplitude of the mainshock adopts the actual recorded PGA, i.e., 0.238 g. The unidirectional eccentric structural model is symmetric in the X direction and eccentric in the Y direction, with eccentricities of 0%, 5%, 10%, 15%, 20%, 25%, and 30%. Only the Y direction is utilized to input ground motion. The running time of the program (110 s) is 40 s longer than the ground motion time, which is used to calm the structural vibration after the mainshock. The response results, including maximum displacements in the X and Y directions, the maximum residual displacement, the torsional angle, the relative torsional effect, and the maximum IDR, are extracted and compared. The maximum displacements of structural models in the Y direction under all eccentricities are shown in Figure 8a. It is evident that as eccentricity increases, the structural displacement also increases, and the increasing speed exhibits a pattern of at first rapid and then slow growth. This indicates that the influence of eccentricity on displacement will gradually weaken with an increase in eccentricity. The maximum increase was more than 2.5 times, at 30% eccentricity. \begin{table}
\begin{tabular}{c c c} \hline
**No** & **Structure** & **Load** & **Abbr.** \\ \hline
1 & Unidirectional eccentric structure & Unidirectional mainshock ground motion & UUM \\
2 & Unidirectional eccentric structure & Unidirectional mainshock–aftershock sequences & UUS \\
3 & Unidirectional eccentric structure & Bidirectional mainshock ground motion & UBM \\
4 & Unidirectional eccentric structure & Bidirectional mainshock–aftershock sequences & UBS \\
5 & Bidirectional eccentric structure & Bidirectional mainshock ground motion & BBM \\
6 & Bidirectional eccentric structure & Bidirectional mainshock–aftershock sequences & BBS \\ \hline \end{tabular}
\end{table} 
Table 7: Seismic dynamic analyses of eccentric structures. Figure 6: The results of the pushover analysis: (**a**) Top floor drift displacement ratio; (**b**) first floor drift displacement ratio. In the X direction, another horizontal direction perpendicular to the Y direction of earthquake loading, the effect of ground motion is very small and almost negligible for the symmetrical structure, as shown in Figure 8b. When the structure produces eccentricity, even if the eccentricity is 5%, a displacement of more than 10 mm can be generated, which is about 1/10 of the Y direction displacement. With an increase in eccentricity, the X direction displacement of the structure becomes larger and larger, showing linear growth until the eccentricity reaches 25%. When the eccentricity continues to increase to 30%, the displacement growth trend slows down in the Y direction. It is anticipated that the displacement decreases in the X direction, possibly as a result of the structure's plane-torsion coupling reaction, which also reflects the complexity of the eccentric structure's torsional response as compared to the symmetric structure's response. In Figure 9, the residual displacements of the structural models show a small fluctuation in certainty scope before the eccentricity rate of 15%. When the eccentricity is in the range of 15-30%, the residual displacement of the structure ascends rapidly, which reflects the structure going into plastic status. Figure 10 shows the trend of the torsional angles for all of the structural models. The torsional angle is one of the important indicators to evaluate the torsional effect of the structure.