斜撐面內挫屈之特殊同心斜撐構件與構架耐震行為研究

Seismic Responses of SCBF with In-Plane Buckling Braces

區瑋衡(Wai-Hang Ao)

指導教授 ： 蔡克銓

國立臺灣大學/工學院/土木工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.00518

摘要

在設計地震作用下，特殊同心斜撐構架須藉由斜撐構件受拉降伏與受壓挫屈進行消能，而傳統斜撐與接合板設計將使斜撐朝面外方向挫屈變形。由先前研究顯示此面外變形量可高達40公分以上，容易對鄰近的人或物造成破壞。採用刀形板的變形作用將斜撐挫屈變形轉變為朝面內方向，本研究透過使用没有浄斷面的刀形板接合設計進行斜撐軸拉壓反復載重試驗以研究含面內挫屈變形斜撐之同心斜撐構架耐震設計方法。研究時利用有限元素分析軟體ABAQUS，以有限元素模型分析輔助研究試體之設計，並以模擬研究試體之反應。

　　本研究共採用五組斷面為H175×175×7.5×11mm, 長度為一組2990與四組3026mm之A36斜撐試體，與曾進行過之兩層樓與三層樓同心斜撐構架試驗採用之斜撐斷面尺寸相同，本研究以平衡法考慮斜撐構件與接合各部不同之韌性要求進行接合設計，刀形板與接合板皆為A572GR50，刀形板凹折區域採用規範建議之三倍板厚線性凹折區域進行設計。各組試體之主要差別在於刀形板的形狀、厚度及其與斜撐接合的細節，試驗藉國震中心之多軸向試驗系統設施進行反覆拉壓測試。試驗結果顯示各組試體反應差別不多，均能發展出設計軸拉與壓力強度，且能承受最大拉應變為+2.5%與最大壓應變為-2.0% 。各組試體破壞模式皆在斜撐中點處先產生局部挫屈，然後才發生全斷面破壞。另外建立有限元素分析軟體ABAQUS，材料模型使用雙線性之實體元素模型來模擬各組試體之反覆拉壓試驗，模擬結果由實驗結果驗證下具有相當之可信度。

考慮施工成本與施工方便性，本研究建議選用TH接合設計作為三層樓構架試體之斜撐接合製作依據。本研究進一步採六組H175x175x7.5x11mm斜撐與TH接合細節研究進行三層構架擬動態試驗時可能會發生的各項試驗反應。分析軟體使用OpenSEES進行動態分析，地震歷時的選擇以三層含挫屈束制斜撐構架擬動態試驗使用過的地震LA03。

透過比對最大頂層位移量、層間位移量、基底剪力以及千斤頂施力需求，本研究建議未來進行擬動態試驗時，六支斜撐斷面改選用H150×150×7×10mm寬翼斷面。以便利繼續使用已有之三層梁柱構架，進行含面內挫屈變形斜撐之同心斜撐構架耐震性能研究。OpenSEES構架分析結果顯示由下至上三層之最大側移角分別將為3.6%、2.8%與0.7%弧度。

關鍵字

同心斜撐構架 ； 斜撐面內挫屈 ； 刀形板 ； 擬動態試驗

並列摘要

Under the strong earthquake, special concentrically braced frames (SCBF) dissipate seismic input energy through cyclic tension yielding and compression buckling of braces. Tradition brace-to-gusset connection design allows the braces to buckle out-of-plane. As observed in the previous tests, the out-of-plane deformation can be greater than 40cm. Thus, the buckling of braces is likely to injure the near-by occupants and cause severe damage on the partition walls covering the braces. The use of knife plate in the brace end connections can transfer the brace buckling direction from out-of-plane to in-plane.

In this research, a total of five 3026mm long H175×175×7.5×11mm, A36 grade wide flange braces are tested in NCREE using the MATS facility. All knife and gusset plates are A572 GR 50. The key differences of the specimens are the shape, thickness of the knife plates and the brace-to-knife plate connection details where a net brace section near the knife plate connection was created or avoided. The Balance Method proposed by others was used in the design of the brace end connection details. All specimens were designed to allow the knife plate to deform using a linear clearance of three times the knife plate thickness. Test results suggest that the cyclic performance of five specimens is similar, all developed the design tensile and compressive strengths of the brace, sustained the peak strains of about +2.5% in tension and –2.0% in compression. All specimens failed due to the fracture of the brace at the mid-span where severe local buckling had occurred. Analytical results indicate that cyclic response of the specimens can be well simulated using the bi-liner soild elements and the ABAQUS model.

Comparing the fabrication cost and the constructability, Type TH connection has been chosen for the brace end connections in the specimen design of a 3-story SCBF. The existing 3-story moment resisting frame has been used with buckling or buckling-restrained braces several times in NCREE. In order to estimate the demands on the horizontal actuators and the vertical anchorage during the pseudo dynamic tests of the 3-story SCBF to be conducted in the future, OpenSEES program and scaled LA03 ground motion records were used.

Based on the analyses, it is concluded in this research that the size of the six braces be reduced from H175×175×7.5×11mm to H150×150×7×10mm due to the limits in the existing laboratory condition. In this manner, it is anticipated that under the 10/50 hazard level earthquake, the peak inter-story drift will reach 3.6%, 2.8% and 0.7% radians in the first, second and third stories, respectively.

並列關鍵字

concentrically braced frame ； brace in-plane buckling ； knife plate ； pseudo dynamic test

參考文獻

[35] 劉家源 (2007),「全鋼型挫屈束制支撐局部挫屈研究劉家源」，國立台灣大學工學院土木工程學系碩士論文，蔡克銓教授指導。

[3] AISC (2005b), “Specification for Structural Steel Buildings”, AISC/ANSI Standard 360-05, American Institute of Steel Construction, Chicago, IL.

[5] B.V.Fell; A.M. Kanvinde, A.M.ASCE; G.G. Deierlein, F.ASCE; and A.T.Myers(2009), “Experimental Investigation of Inelastic Cyclic Buckling and Fracture of Steel Braces”, Journal of Structural Engineering, ASCE, Vol. 135, January.

[6] Chen, C.H., Lai, J.W. and Mahin, S.A. (2008), "Seismic Performance Assessment of Concentrically Braced Steel Frame Buildings", 14WCEE

[7] Chen, C.H., Lai, J.W. and Mahin, S.A.(2008), “Numerical Modeling and Performance Assessment of Concentrically Braced Steel Frames”, Proceedings, ASCE SEI 2008 Structures Congress, Vancouver, Canada.