## 4 Time History Analysis
### Acceleration Response  
The magnitude of structural acceleration reflects the intensity of inertial forces experienced during seismic excitation. As shown in Figures 13-16, the absolute acceleration values at each floor increase significantly with the intensification of the input ground motion. Moreover, the acceleration distribution trends vary markedly under different earthquake records. This variation is primarily attributed to differences in the spectral characteristics of each seismic wave, where the coupling between specific frequency components and the structure's natural frequencies at various modes leads to distinct floor-level acceleration response patterns. Particularly under earthquake records with broader spectra and substan  
Figure 12: Ground motion selection. (**a**) Acceleration time history of Wenchuan ground motion; (**b**) acceleration time history of El Centro ground motion; (**c**) acceleration time history of Chi-Chi ground motion; (**d**) Wenchuan Fourier amplitude spectrum; (**e**) El Centro Fourier amplitude spectrum; (**f**) Chi-Chi Fourier amplitude spectrum; (**g**) acceleration time history of Hector Mine ground motion; (**h**) Hector Mine Fourier amplitude spectrum.  
tial mid-to-high frequency components, such as the Wenchuan and El Centro records, the floor responses across different grain-loading scenarios exhibit pronounced differentiation.  
Further analysis of the influence of different grain-loading conditions reveals that top-loaded configurations (e.g., FFE, FFF), due to greater mass at the upper levels, produce a more balanced overall mass distribution, thereby enhancing global structural stiffness and reducing the top-floor acceleration amplification. In contrast, bottom-loaded conditions (e.g., EEF, EFF) are characterized by lower upper mass, making the structure more vulnerable to excitation by mid-to-high frequency components in the ground motion, resulting in significant acceleration amplification at the top floor. For instance, under the Wenchuan and El Centro records, the peak top-floor acceleration in the EFF scenario increased by  
Figure 14: Acceleration response under El Centro ground motion.  
Figure 13: Acceleration response under Wenchuan ground motion.  
Figure 15: Acceleration response under Chi-Chi ground motion.  
76.12% and 70.49%, respectively, compared to the FFF scenario (Figures 13 and 14), while under the Hector Mine record, the EFF case showed a 62.79% increase over the EEF case (Figure 16).  
Notably, in the empty warehouse condition (EEE), the reduced structural mass and relatively higher stiffness can lead to strong resonance or near-resonance effects when the dominant frequency of the ground motion aligns with the structure's natural frequency. This results in significantly amplified top-floor responses. For example, under the Chi-Chi earthquake, the peak top-floor acceleration in the EEE case was 104.67% higher than that in the FFF case (Figure 15), highlighting the heightened sensitivity of the structure in an empty state to specific ground motion characteristics.  
The acceleration time histories at the roof level under different ground motions are shown in Figure 17; the peak acceleration values and overall response patterns under different earthquake records vary significantly across grain-loading scenarios. This indicates that the structural acceleration response of multi-floored grain warehouses is highly sensitive to the specific grain-loading configuration. In particular, scenarios such as EFF and EEE, characterized by lighter mass in the upper floors or reduced total mass, are more prone to acceleration amplification under seismic excitation. In contrast, the FFE condition, with a relatively balanced grain distribution across floors, demonstrates more stable and moderate top-floor acceleration responses.  
Figure 16: Acceleration response under Hector Mine ground motion.  
Figure 17: Cont.