中高樓斜撐建築物受山腳斷層及遠域地震之耐震行為

Abstract

根據前人研究顯示，由於近斷層地震含有大量能量輸入結構且會使地表產生大量的永久位移，因此將對結構產生較大的反應；近斷層地震又分為有速度脈衝及無速度脈衝之地震動歷時，其中有速度脈衝之地震可能與斷層破裂方向性及與斷層破裂面之距離有關，本研究建立三種不同樓層數之構架，分別為8層樓、14層樓與25層樓，代表中週期至中長週期的結構，並針對山腳斷層及臺北一區MCE設計地震中有、無速度脈衝之地震動歷時進行比較，分別探討結構中最大層間位移、殘餘側位移等結構反應，比較有、無速度脈衝之地震記錄於動力歷時分析中對結構造成的差異。由於本研究將各構架工址假設位於新北市泰山區，以建築物耐震設計規範定義此地區分類為臺北一區，然而此區域並無考慮近斷層效應，本研究考量到山腳斷層若在未來發生錯動時將可能對人口稠密的臺北盆地造成嚴重影響，因此將山腳斷層錯動下可能之地震動歷時與臺北一區最大考量地震進行比較，探討兩種反應譜作用下不同週期結構之反應。本研究於各構架中皆分別配置不同種類的消能斜撐，包含夾型挫屈束制斜撐、交錨型雙核心自復位斜撐及假設彈性勁度、後彈性勁度皆與挫屈束制斜撐相同之自復位斜撐，利用非線性靜動態三維結構分析程式PISA3D進行非線性動力歷時分析，探討於相同地震歷時作用下三種不同類型之斜撐對結構耐震行為之差異。 分析結果顯示，8層樓構架於有速度脈衝的山腳斷層地震作用下約比無脈衝地震作用下其層間位移角大約10%，對14層樓及25層樓構架，有脈衝地震比無脈衝地震其層間位移角大約15至20%，而在MCE層級地震作用下無論有、無速度脈衝，其最大層間位移角差異皆小於10%；以結構殘餘側位移來看，本研究中8層樓構架無論在何種反應譜地震作用下，有脈衝地震與無脈衝地震對於殘側位移差異不大，對於14層樓與25層樓構架而言，有脈衝地震其殘餘側位移分別為無脈衝地震作用之1.3至1.6倍及1.4至2倍。此外，配置三種斜撐之構架皆可有效降低結構最大層間位移角，其中配置交錨型自復位斜撐之效益尤其明顯，且交錨型自復位斜撐亦能大幅降低結構受到地震作用後之殘餘側位移，而挫屈束制斜撐雖能有效降低結構層間位移角，但對於降低結構殘餘側位移的效果相當有限；另外，配置自復位斜撐之構架在結構受到地震力作用下仍能保持良好的消能能力，而挫屈束制斜撐在產生大量殘餘變形後將降低其消能能力。本研究中各構架無論在山腳斷層地震或MCE設計地震作用下其最大層間位移角平均值皆小於ASCE 7-16及FEMA P-1050-1 (2015)建議之3%。除此之外，本研究中25層樓BRB構架於MCE地震作用下其殘餘側位移平均值超過FEMA P-58-1 (2018)建議之0.5%，因此該構架可能於地震作用後無法繼續使用，然而若將BRB改為SCB1，在相同地震作用下可使結構殘餘側位移小於0.5%，滿足此規範之建議，顯示SCB1能大幅減少結構殘餘側位移之特性。

According to previous studies, near-fault earthquakes not only contain a large amount of energy input to structures, and cause a large number of permanent ground displacement, these characteristics may cause severe damage to structures. Near-fault earthquakes can be divided into pulse-like and non pulse-like ground motions, among them, pulse-like ground motions may be related to forward-directivity and the distance to the rupture surface. Three different story of structures were established in this study, representing the medium to long period structures. From the structural response point of view, comparing maximum interstory drift, residual interstory drift and maximum accelerarion between Shanchiao fault and maximum considered earthquake in Taipei zone 1, also compare the different response in structures between pulse-like and non pulse-like ground in nonlinear time history analysis. Since the structures in this study is located in Taishan District, New Taipei City, the area is classified as Taipei Zone 1 in Taiwanese seismic code. However, the near-fault effect isn’t considered in current seismic code, Considering that will have a serious impact to Taipei Basin if Shanchiao fault dislocated in the future, in this study, difference of structural response between the possible ground motions of Shanchiao fault and maximum considered earthquake in Taipei zone 1 were considered. In this study, three types of braced frame were considered, including sandwiched buckling-restrained braces, dual core self-centering braces and the self-centering braces that its elastic stiffness and post-elastic stiffness are same with BRB, using nonlinear analysis program, PISA3D, exploring seismic behavior in three types of braced frame under the earthquakes. The results show that the interstory drift of 8-story frame with pulse-like records is about 10 % higher than non pulse-like records under Shanchiao fault earthquakes, For 14-story and 25-story frames, pulse-like records is about 15% to 20% higher than non pulse- like records under the same ground motions. In MCE level, the difference between interstory drift is lower than 10% whether it is pulse-like or non pulse-like records in all of the frames. In addition, the difference of residual interstory drift is greater between pulse-like and non pulse-like records when the total number of stories in the structure is higher. The structure with braces can reduce the maximum interstory drift effectively, among them, the dual core self-centering braces is the most obvious. Self-centering braces can also greatly reduce the residual interstory drift when structures subjected to the earthquakes. BRB can reduce the interstory drift of structures, however, the effect on reducing the residual interstory drift is not effective. In addition, SCB frames can maintain a good capacity of energy dissipating under the near-fault ground motions, but BRB would reduce its capacity after a large amount of residual deformation occurs. In this study, the mean of interstory drift is less than 3% whether its subjected to Shanchiao fault or MCE ground motions, which satisfies the recommendations of ASCE 7-16 and FEMA P-1050-1 (2015). In addition, the average of residual interstory drift of 25-story BRB frame exceeds 0.5% under MCE ground motions, which exceeds the recommendations by FEMA P-58-1 (2018), so the frame may not be able to be used after the earthquake. However, if we replace BRB with SCB1, the mean of residual interstory will less than 0.5% under the same ground motions.