| dc.description.abstract | It may be observed that near-fault earthquakes have pulse caused by forward-directivity effects in velocity time history, or permanent displacement due to fling effects in displacement time history, both of which have long-period velocity pulses. If the structure foundation period is close to the pulse period, it may cause serious damage to the structure. However, the current codes only use the near-fault amplification factors NA and NV to amplify the design requirements for near-fault sites, and do not make considerations for the long-period velocity pulse. In addition, the high mode effects that high-rise buildings may cause, the nonlinear behaviors caused by special buildings, and the faster and faster calculation speed of analysis software in the engineering industry all show the necessity and feasibility of nonlinear time history analysis. However, the current domestic codes do not specify the selection and scaling methods for near-fault ground motion. In this study, firstly, the records of Chi-Chi earthquake in 1999 were used to discuss the characteristics of near-fault ground motions, and to preliminarily study the applicability of pulse period Tp. Based on the characteristics of pulse-like ground motion, and relied on the current code design spectrum, a specific suggestion method for nonlinear time history analysis of near-fault sites is proposed. Finally, using the proposed method, five representative near-fault earthquakes and two far-field earthquakes were input into steel structure buildings of eight-, fifteen-, and thirty-stories building. We used the commercial software ETABS 2017 to conduct nonlinear time history analyses to explore the impact of near-fault earthquakes on structural steel buildings of different heights. During the research, it was observed that the domestic seismic design code for high-rise (large period) buildings has excessively large roof forces in the vertical distribution of seismic forces. It is recommended to change the distribution method according to ASCE7.
The results of this study show that the pulse-like ground motion of forward-directivity effect is likely to produce high-mode effect on the structure, and may have an unfavorable impact on the high-rise buildings. However, permanent displacement caused by the fling will cause a larger story drift ratio on the lower floors, which may be more dangerous to the structures. It is recommended that near-fault sites need to perform nonlinear time history analysis to consider the characteristics of pulse-like ground motions. The construction on near-fault sites requires special attention to its applicability and notification of the negative impact caused by near-fault pulse-like ground motions on structures. | en_US |