Comparison of the earthquake response of super-high-rise structures based on different seismic design spectra
To evaluate the reliability of seismic design spectra in the long-period segment, two super-high-rise structures with long-period national vibration period are analyzed using response spectrum superposition method and dynamic time-history analysis method. The maximum displacement response of the structural top and the maximum earthquake shear response of the structural base are compared. According to the long-period segment spectrum stipulated in the Japanese and Chinese seismic design codes, the displacement spectra calculated based on a quasi-spectral relationship obviously amplify with the increase of the vibrational period. This is not consistent with the statistical attenuation characteristics of the displacement response spectrum. When following the design spectrum of the Japanese or Chinese seismic design codes, the maximum displacement response calculated by the response spectrum method is significantly higher than the average result calculated using a dynamic time-history analysis method. However, the difference between the maximum displacement response calculated in accordance with the design spectrum stipulated in US seismic design codes and our proposed design spectrum and the average results calculated by the time-history analysis method is significantly smaller. Therefore, the proposed design spectrum and the US seismic design codes are more reliable in this regard. The maximum base earthquake shear force calculated in accordance with the response spectrum method in the proposed design spectrum is consistent with the average results calculated by the dynamic time-history analysis method, as well as the results calculated according to the design spectrum methodology in China and the seismic design codes utilized in the US. However, the proposed design spectrum better characterizes the shear response of the long-period structures of high-order vibration modes. For large long-period structures, the maximum displacement response calculated in accordance with the design spectrum in the Chinese seismic design codes increases with the structural damping ratio. The amplitude variation of the maximum shear force of the structural base is very small. This indicates that the long-period segment in the design spectrum stipulated in the Chinese seismic design code is not very reasonable. For large long-period structures, as the damping ratio increases, the increasing ratio of the damping force to the structural system’s internal force cannot be ignored. Therefore, the reduction ratio of the damping force in the long-period segments of the response spectrum should be appropriately selected.
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