| Long-period ground motions are generally referred to as far-field ground motions,with a predominant period ranging from a few seconds to a dozen seconds,and studies indicate that the response characteristics of high-rise buildings and super high-rise buildings under longperiod ground motions are significantly different from those under ordinary ground motions.However,existing studies mostly focus on the comparison of the structural response values under long-period ground motions and ordinary ground motions,rarely on the distribution characteristics and rules of structural response along floors,and have not clarified the inherent mechanism of the differences in structural response characteristics under long-period ground motions and ordinary ground motions.Therefore,RC-framed shear wall structure is selected as the object of this paper.The characteristics of the ground motions,the comparison of the dynamic response characteristics of RC frame-shear wall structure,the influence mechanism of seismic frequency domain characteristics on structural response characteristics,and structural seismic design and strength methods considering the low-frequency characteristics of longperiod ground motions were studied and analyzed for long-period ground motions and ordinary ground motions.The main research contents include:(1)Analysis of the characteristics of long-period ground motions.One hundred representative records of long-period ground motions and ordinary ground motions were selected.The peak value,duration,spectrum,and energy distribution characteristics of two types of ground motions are compared and analyzed.The results indicate that the low-frequency component of long-period ground motions is abundant and mainly concentrated around 0.1 Hz to 0.4 Hz.The energy is mainly concentrated in the low frequency range of 0 Hz to 1 Hz and distributed more uniformly in the time domain,and it shows long-duration low-frequency vibration in the time history.(2)A comparative analysis of the response characteristics of RC frame shear wall structure under long-period ground motions and ordinary ground motions.Twenty representative records of the two types of ground motion were selected,and three RC frame-shear wall structure models were established with different basic structural natural periods,and a non-linear dynamic time-history analysis was performed based on Perform-3D.The numerical characteristics and distribution rules of displacement,drift,shear force and shear force ratio,hysteretic energy,and member hysteretic energy of the structure under different ground motions were compared.The results indicate that,with the increase in peak acceleration of ground motions intensity compared with ordinary ground motions,the increase in hysteretic energy of the structure under long-period ground motions is the largest,ranging from 32 to 904.But the degree of downward shift of the floor with the maximum hysteretic energy is smaller than that of the drift,and the maximum hysteretic energy is more concentrated along the floors and mainly concentrated in the height of 1/3 to 2/5 of the structure,and the change in internal force response is the smallest.(3)Analysis on the influence mechanism of low-frequency characteristics of long-period ground motions on structural response characteristics.Taking a 20-story RC frame shear wall as an example,different frequencies of harmonic waves and reconstructed ground motions based on EMD were selected as excitations for time-history analysis to analyze the influence of excitation frequencies and frequency-domain components(IMF)on structural response characteristics.Based on the simplified structural dynamic calculation model,the mechanism of the change in the distribution pattern of structural response under long-period ground motions is theoretically analyzed from the perspective of strikeout participation.The results showed that the elastic response of the structure first increased and then decreased with the increase of the excitation period,reaching a maximum at the period of 1.1T.The IMF component closest to the natural period of the structure has the greatest influence on the structural response.The elastoplastic response of the structure continued to increase with the increase of the excitation period,and the same IMF component had different degrees of influence on different responses.The low-frequency characteristics of long-period ground motions can increase the participation of low-order strikeouts of the structure,affecting the structural response characteristics.(4)Seismic design and reinforcement suggestions for structures considering the influence of low-frequency characteristics of long-period ground motions.Combining the results of this paper and existing research to quantify the response characteristics of high-rise structures of different types and heights under the action of long-period ground motions.The results showed that with the increase of the low-frequency components and intensity of ground motions,structures of different types and heights showed a trend of response increase and maximum response shifting downward along the floor distribution.Among them,the increase in hysteretic energy was much greater than that of internal forces and displacements and increased up to 904 times.Finally,seismic design and strengthening suggestions for high-rise structures considering the influence of low-frequency characteristics of long-period ground motions were proposed. |
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