| 摘要: | 近斷層地震可能在速度歷時上觀察到由指向性效應造成的脈衝波，或是位移歷時因斷層滑移效應產生永久地表位移的現象，兩者皆有長週期的速度脈衝。若是結構週期與速度脈衝週期相近，可能會造成結構較嚴重的破壞。然而，目前國內規範針對近斷層地震僅以近斷層放大因子NA、NV放大設計需求，並未針對近斷層地震動長週期速度脈衝特性做設計上考量。此外，高樓建築可能造成的高模態效應、特殊建築造成的非線性行為以及工程業界分析軟體運算速度越來越快都顯示出非線性動力分析(歷時分析)的必要性及其可行性，然而目前國內規範僅簡單敘述非線性動力分析方法，並未特別提及近斷層地震地震紀錄選取及縮放方法。本研究首先以1999年集集地震地震紀錄探討近斷層脈衝型地震動特性、初步研究脈衝週期Tp的合理性以及適用性。利用近斷層脈衝型地震動特性研究結果，以現行規範設計反應譜為基準，提出近斷層工址進行非線性動力歷時分析的具體建議方法。最後利用所提出之方法將五筆代表性近斷層地震以及兩筆遠域地震分別輸入至八層、十五層、三十層樓鋼結構建築(分別代表一般樓高、中高樓高、高樓高建築)，以商業軟體ETABS 2017版本進行非線性動力歷時分析，探討近斷層地震對不同樓高鋼結構建築造成的影響。此外，研究過程中發現國內耐震設計規範對於高樓(週期大)建築地震橫力豎向分配之屋頂剪力過大的情形，建議以美國規範ASCE7的分配方式更改之。
本研究結果顯示指向性效應之脈衝型地震動很有可能對使結構產生高模態效應，對高樓建築可能產生較不利的影響；而斷層滑移造成之永久地表位移會使結構低樓層處產生較大的層間位移角，對低樓層處產生較為嚴重的破壞。建議近斷層工址需進行非線性歷時分析，以考量脈衝型地震動特性、真實模擬結構非線性行為進行檢核。近斷層工址建築物的興建需特別注意其適用性、考量近斷層脈衝型地震動對結構的負面影響。
;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. |
