## 4 Comparative Analysis of Theoretical and Experimental Results
### Seismic-Response Analysis under Single and Bidirectional Seismic Motion  
#### 4.3.1 Comparison of Floor Acceleration Response  
Figure 26 shows the comparison between the average absolute peak acceleration values of rigid and soft soil interlayer isolation under four types of seismic motions with an acceleration of 0.2 g in the X-direction and bidirectional input.  
Figure 26: Comparison of acceleration amplification coefficients under single and bidirectional ground motions (PGA = 0.2 g). (**a**) Near-field ordinary ground motion; (**b**) Far-field ordinary ground motion; (**c**) Near-field pulse ground motion; (**d**) Far-field harmonic ground motion.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Model** & **Calculated Value/s** & **Experimental Value/s** & **Error/\%** \\ \hline Rigid-interlayer isolation & 0.463 & 0.455 & 1.76 \\ Weak soil interlayer isolation & 0.558 & 0.543 & 2.76 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Comparison of natural vibration periods of model structures.  
Figure 26 shows that when the PGA is 0.2 g, the impact of different seismic input forms on the acceleration response of the substructure is significantly smaller than when PGA = 0.1 g. The difference in the acceleration response of the substructure between the two systems is relatively small under unidirectional seismic input. It can be inferred that as the peak acceleration of input seismic motion increases, the acceleration response of the rigid and soft soil interlayer isolation systems under the bidirectional seismic motion is closer to that of the unidirectional input seismic motion. Under the action of single and bidirectional input ordinary seismic motions, the maximum acceleration amplification coefficients of the lower structure of the rigid and the soft soil interlayer isolation system are significantly greater than those of the upper structure; especially, after considering the SSI effect, the acceleration response of the upper structure is significantly weakened. Under the action of single and bidirectional input long-period seismic motions, although the SSI effect has a certain weakening effect on the acceleration response of the upper structure, the acceleration amplification coefficient of the top layer of the upper structure is still close to that in the rigid foundation condition. Therefore, for the design of interlayer isolation structures under a soft soil foundation under long-period seismic coupling conditions, the research focus must be on the safety of the top layer of the upper structure. Furthermore, when considering the influence of SSI effect, the acceleration response of the upper structure decreases; however, with the increase of PGA, the weakening of the acceleration response under long-term seismic motion is smaller than that under ordinary seismic motion. Under the action of 0.2 g ordinary seismic motion, the maximum amplification coefficient of the top layer acceleration of the upper structure on the rigid foundation is 1.32, and it is 0.74 on a soft soil foundation. Under the action of 0.2 g long-period seismic motion, the maximum acceleration amplification coefficient of the top layer of the upper structure on the rigid foundation is 2.06, and it is 1.74 on the soft soil foundation. However, considering the SSI effect, the acceleration amplification coefficient at the top of the lower structure is significantly greater than that at the top of the upper structure. Therefore, in the structure design, the safety of the lower structure must be focused on under the earthquake action.