國家地震工程研究中心新建與既有樓板接合分析與設計

Analyses and designs of the connections jointing the new steel structure and the existing RC structure in NCREE's office building extension

林昱成(Yu-Cheng Lin) ； 莊明介(Ming-Chieh Chuang) ； 林冠泓(Guan-Hong Lin) ； 鄧彬斌(Pin-Pin Deng) ； 蔡克銓(Keh-Chyuan Tsai) ； 蔡青宜(Ching-Yi Tsai) ； 吳安傑(An-Chien Wu) ； 林瑞良(Jui-Liang Lin)

《結構工程》 38卷1期 (2023/03) Pp. 31-62

https://doi.org/10.6849/SE.202303_38(1).0002

摘要

國家地震工程研究中心為因應發展，於2019年10月至2020年11月，在既有六層樓鋼筋混凝土（reinforced concrete, RC）辦公大樓上，增建七層樓成為十三層RC、鋼骨鋼筋混凝土與鋼結構的複合結構。本文介紹二樓至七樓新建服務核樓板及鋼梁與既有RC結構接合處的分析與設計。本研究以梁腹側角鋼加勁，同時考量托架有無封板的型式，探討三種接合設計，並進行一系列的有限元素分析。經Abaqus有限元素模型推估接點元素在交界面的軸向勁度為100 tf/mm，配合PISA3D結構分析軟體建立十三層增建大樓的結構模型，進行16組地震的非線性反應歷時分析，二至七樓新舊樓板採雙質心雙剛性樓板的設定，並用6自由度接點元素來分析新舊樓板交界面接頭的受力。經PISA3D歷時分析結果可得二至七樓服務核與既有RC結構交界處之單一梁端最大軸力以及最大層間位移角，分別為165 tf以及1% rad。本研究以保守方式，在不考慮樓板的貢獻，以上述力量和變形作為接頭的設計需求，再對各個接合設計進行Abaqus有限元素分析，接頭錨栓採用只受拉之線性彈簧，另以只受壓之線性彈簧來模擬接頭端鋼板抵靠於RC面之邊界條件，並在梁端反曲點3,800 mm處同步施以軸拉1.5 mm與面內向上40 mm之位移，來模擬設計地震下之設計需求。分析結果顯示基本設計的接頭型式，直托架接合之托架腹板產生明顯剪力降伏並可觀察到錨栓受力不均的情形。三種改良方案中，比較結果後可知新增封板能使錨栓最大受力降低35%以上，且封板傳力使錨栓受力分布均勻的效果顯著。此外，在封板角落可切除短邊長為200 mm之等腰直角三角形低應力區塊，以利未來錨栓受震後的安全性檢查。本研究確認以雙腹側角鋼加勁及直托架封板切角式為最佳方案，除能符合設計需求，可使梁發展出韌性較好之彎矩塑鉸，並具可供未來檢視錨栓的開孔。

關鍵字

國家地震工程研究中心 ； 耐震設計 ； 接頭補強 ； 化學錨栓 ； 有限元素模型分析 ； 非線性反應歷時分析

並列摘要

The existing six-story office building of the National Center for Research on Earthquake Engineering (NCREE) was extended to thirteen-story from October 2019 to November 2020. This study presents the analysis and design of the connections jointing the existing RC structure and the new steel service core from the second to seventh floors. A steel bracket, which is welded to the steel beam bottom flange and connected to the RC column using chemical anchors, was considered as the basic design of the connection to transfer the gravity shear from the steel beam. This shear connection detail could avoid the congested reinforcing bars inside the RC beam-to-column joint, however, three alternative designs using strengthened schemes are investigated in this study. Nonlinear response history analyses (NRHAs) using PISA3D program for the NCREE's 13-story composite building were conducted in order to gain insight into the possible maximum seismic force and deformational demands on the connections. The features of dual mass centroids and dual rigid diaphragms for the second to seventh floors are incorporated into the PISA3D model. The 6DOF joint elements are utilized to represent the aforementioned bracketed connections on the interface. The axial push-pull stiffness of 100 tf/mm, computed from an Abaqus finite element model (FEM) analysis for the connections, is utilized for all the 6DOF joint elements. A total of sixteen sets of ground accelerations are utilized. NRHA results indicate that the maximum axial force and maximum in-plane rotation of the connection at the steel beam end are about 165 tf and 0.01 radian, respectively. The Abaqus FEM analyses were conducted for investigation of four connection types including the basic design and three improved designs. The FEM analysis results indicate that the beam bracket of the basic design exhibits obvious shear yielding. The uneven anchor bolt forces developed are very evident. The improved load-carry capacity and a more uniform bolt forces developed are found in the strengthened designs, such as the stiffened steel angles at the beam web and bracket with cover plate. In addition, an approximately 200×200 mm triangular region on the cover plate corner with a low stress demand is observed. Based on these connections' FEM analysis results, this study confirms that the strengthened scheme adopts double-sided stiffened steel angles at the beam web, the straight bracket with the angular cuts on the cover plates is suitable. The strengthened scheme adopted in the project not only meets the seismic demands but also allows the inspections of the anchor bolts in the future, if necessary.

並列關鍵字

seismic design ； strengthened connection ； chemical anchor ； finite element analysis ； nonlinear response history analysis

參考文獻

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內政部營建署(2011a)，「建築物耐震設計規範及解說」。