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  • 學位論文

槽接式挫屈束制支撐構件軸向扭轉行為研究

Torsional Response of Welded End-Slot Buckling-Restrained Brace

指導教授 : 蔡克銓

摘要


挫屈束制支撐(BRB)為可靠之耐震消能構件,近年來廣泛運用於耐震建築結構系統。槽接式挫屈束制支撐(WES-BRB)之核心單元包含一片核心板與兩片加勁板,核心板與隅板垂直,且於核心板接合段端部之中央開槽;兩塊加勁板與核心板垂直,分別位在核心板兩面之開槽兩側,並且以填角銲或開槽銲與核心板連接。WES-BRB之特點為其開槽接合形式,核心板開槽處插入隅板,利用加勁板與隅板之三邊緣以銲接接合,使得接合段長度大幅降低、提升接合部之穩定性。經過多次構件、構架試驗觀察到WES-BRB隨著軸力拉壓而產生軸向些許扭轉之行為,其軸向扭轉力學行為之成因、以及如何減緩扭轉角度為本研究探討重點。 WES-BRB受軸力扭轉之行為來自其斷面與銲接接合形狀,其主要原因有二:1.核心單元斷面上軸力傳遞時,其通過轉換段到達接合段,力量沿著轉換段的漸變斜度傳遞,轉換段處之斷面將會有成對且等大的剪力分量分別存在於核心板與加勁板上;又由於兩加勁板彼此錯開一個開槽寬度,使得剪力有了力臂,進而產生扭矩使得斷面扭轉。2.接合段端部形成兩個角鋼形狀,但銲道配置將產生剪力遲滯效應,若看其中一個角鋼,在遠端核心段處軸力作用於一側角鋼之形心上,當軸力傳遞至接合段時,合軸力將會漸漸地轉換作用於銲道配置的形心上,如此將使得接合段角鋼斷面上產生剪力分量。若同時考慮接合段之兩個角鋼,剪力分量搭配槽接式斷面錯開十字的力臂,對全斷面形心造成扭矩,使得斷面產生扭轉。比較剪力遲滯效應影響程度,若兩形心偏心距離愈大,在相同軸力作用下,斷面上之扭矩應愈大,而扭轉角度應也會較大。本研究主要針對如何降低銲道形心與核心段角鋼形心的偏心距,擬定之減緩扭轉角度方案有二:1.利用平衡銲道配置,不改變支撐插入隅板之長度,但調整接合段三邊銲道之長度,以降低兩形心偏心距離。2.調整斷面核心板與加勁板之尺寸,以降低兩形心偏心距離。 本研究先以既有之WES-BRB實驗案例建置ABAQUS有限元素模型,確認能夠準確模擬其受力變形與扭轉反應,再進一步探討所提出之減緩扭轉方案之效益,有限元素模型分析結果顯示平衡銲道、調整斷面核心板與加勁板之尺寸配置皆能有效減緩扭轉,同時也確認軸力方向與軸向扭轉方向之關係。基於有限元素分析結果,本研究設計五組不同偏心量之WES-BRB試體,於國家地震工程研究中心進行反覆載重試驗,包含兩組採傳統方形圍束鋼管與三組採薄型圍束鋼管。其中一組方形圍束鋼管採取平衡銲道接合細節,三組薄型圍束鋼管則是改變核心板厚度與轉換段形式。試驗結果顯示:1.最大軸向扭轉角度皆發生於圍束鋼管,在經歷最大核心應變0.03下,最大軸向扭轉角度不大於1.5度,各圈扭轉角度正負峰值差距之最大值不超過2.5度。2.偏心量愈小,最大軸向扭轉角度與各圈扭轉角度正負峰值差距之最大值愈小,試驗結果與預測吻合。3.平衡銲道配置使軸向扭轉量較原銲道配置者約減低50%。4.扭轉反應對於消能行為幾乎沒有影響,所有試體之累積塑性變形量皆遠超過AISC2010規定之200。5.抗疲勞性能良好,不同疲勞應變大小下之疲勞壽命變化趨勢接近前人所提出之迴歸結果。本研究經有限元素模型分析與構件實驗確認WES-BRB些許扭轉反應之成因,且證實減緩WES-BRB軸向扭轉角度之方法,可供WES-BRB設計者參考應用。

並列摘要


The welded end-slot buckling-restrained brace (WES-BRB) features a reduced length of the connection segment thus improving the stability of the BRB end-to-gusset connections. The WES-BRB core member consists of one core plate slotted along the centerline at two ends, and two rib plates welded perpendicular to the core plate along two edges of the slot in opposite surfaces of the core plate. The core plate is oriented perpendicular to the gusset plate. By using the slot on the core plate, the core member can be inserted into the gusset plate before welding the edges of the rib and core plates onto the gusset plate. Numerous brace component and frame tests have confirmed the excellent performance of the WES-BRBs. However, a very slight twisting of about 1.0 to 2.0 degrees along the BRB axis could be detected when it is subjected to an axial strain of 0.03. The objectives of this research are to investigate the WES-BRB twisting mechanism and to develop the improved designs for a reduced twist angle. Under the axial load, it can be found that the WES-BRB twisting is attributed to two reasons: (a) When an axial load passes through the transition segment, a pair of shear forces of equal magnitude but in opposite direction will be developed on the cross sections of the two rib plates due to the tapered transition shape. The shears and their distance form the torque and twist the cross section. (b) Near the connection, the core member can be viewed as two angles. The BRB end-to-gusset welding details result in a shear lag effect for each angle. This means the axial force acts through the centroid of one angle in the core segment, but through the centroid of the welds at the end connection. The eccentricity between the above two centroids will develop two pairs of shear force components, each equal in magnitude and opposite in direction. These would form the torque and twist the cross section. Reducing these eccentricities would reduce the twist angle. Thus, the followings two approaches are proposed to reduce the eccentricities: (a) considering the same end connection length to the gusset, but applying a balanced weld detail in arranging the weld length on different edges; (b) re-arranging the dimensions of the core and rib plates. In this research, past test results of one WES-BRB are firstly analyzed using ABAQUS finite element model (FEM). The analytical axial force versus axial and torsional deformation relationships well agree with the test results. Furthermore, the effectiveness of the proposed methods in reducing the twist angle is confirmed by the FEM analyses. Based on analysis results, a total of five WES-BRB specimens, including two with square restraining steel casing and three with rectangular restraining steel casing, are designed and tested at NCREE by using cyclic loading procedures. One of the WES-BRB with square steel casing adopts the balanced weld, and three with rectangular steel casing adopt two types of transition segment while different thicknesses for the core and rib plates are used. Key test results include: (a) the twist angles of the steel casing are slightly greater than the core section outside the steel casing in all the five specimens. Under the core strain of 0.03, the maximum twist angle and the maximum difference between the positive and negative twist angles in one loading cycle are less than 1.5 and 2.5 degrees, respectively; (b) it is confirmed that a smaller eccentricity results in a smaller twist angle; (c) compared with the weld-all-around connection details, using the balanced weld reduces the maximum twist angle by about 50%; (d) torsional response has no apparent influences on the stiffness, strength or cumulative plastic deformation capacity of all specimens; (e) all specimens possess good fatigue performance and the fatigue life can be predicted using the empirical results proposed by others. This research investigates the twisting mechanism of the WES-BRB and confirms the effectiveness of the proposed designs in reducing the twist angle. Results can be used to advance the seismic design of WES-BRB and the connections.

參考文獻


21. 林保均,(2010),「含薄型挫屈束制支撐構架耐震行為研究」,國立台灣大學土木工程研究所,碩士論文,蔡克銓教授指導。
20. 蔡克銓、吳安傑、林保均、魏志毓與莊明介,(2012),「槽接式挫屈束制支撐與脫層材料性能研究」,結構工程,第二十七卷,第三期,第29-59頁。
2. AISC 360-10 (2010). Specification for Structural Steel Buildings. American Institute of Steel Construction, Chicago.
3. AISC(American Institute of steel Construction) 341-10 (2010). Seismic Provisions for Structural Steel Buildings. American Institute of Steel Construction, Chicago.
4. Black, C.J., Makris, N. and Aiken, I.D. (2004). “Component testing, seismic evaluation and characterization of buckling-restrained braces.” Journal of Structural Engineering, 130(6), 880-894.

被引用紀錄


張捷安(2014)。含平板狀核心挫屈束制支撐圍束單元局部外突破壞行為研究〔碩士論文,國立臺灣大學〕。華藝線上圖書館。https://doi.org/10.6342%2fNTU.2014.01453

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