銲接型雙WT斜撐與隅板接合行為分析與試驗研究

Analysis and Experiment of Welded Double-WT to Gusset Connections

陳師睿(Shih-Jui Chen)

指導教授 ： 蔡克銓

國立臺灣大學/工學院/土木工程學系/碩士(2024年)

https://doi.org/10.6342/NTU202402433

摘要

同心斜撐構架 (Concentrically Braced Frame, CBF) 為鋼結構中廣泛使用之耐震系統之一。其非彈性側向反應仰賴著斜撐構材、隅板與梁柱構架桿件，其中主要以斜撐構材抵禦地震以及風力等側向力。其具有較高的施工便利性，且梁與柱構件的尺寸將可減小，因此可提高整體結構系統之經濟效益。另外，不論是何種形式的斜撐，一定都需要接合隅板 (gusset plate) 幫助其連接母構架，因此隅板的力學行為十分重要，其傳力機制會直接影響斜撐的耐震表現。本研究結合斜撐及隅板，針對雙WT銲接型同心斜撐隅板受壓挫屈強度以及受面外彎矩行為進行實驗及分析研究，對規範以及既有理論計算做修改建議，使隅板的設計能更經濟且安全。本文先使試體設計符合現實且安全，並建立有限元素模型，探討隅板之挫屈強度、塑性彎矩容量以及旋轉勁度。為驗證理論所得及所提設計方法，本研究針對隅板受壓挫屈及受面外彎矩行為建立兩套試驗配置，設計八組試體，五組測試隅板挫屈強度，以不同的隅板厚度、形狀大小以及有無邊緣加勁板為變數；另三組測試隅板塑性彎矩，使用不同的偏心大小以及有無邊緣加勁板為變數。在隅板挫屈有效寬度計算，建議取擴張角45°，且有效長度係數K值在隅板未加勁時取1.3；有單邊加勁時取1.0，設計結果與試驗及有限元素分析結果最多僅差7%，若欲在設計上須更方便且保守些，擴張角亦可取37°進行計算。且從試驗及有限元素分析結果得知，若要增加隅板挫屈強度，直接增厚隅板厚度會較添加邊緣加勁板更有效率。根據本研究結果，隅板受面外彎矩，受彎之凹折線分佈，宜取離隅板斜撐接合段底部2tg位置更適合計算塑性彎矩Mp,g，所提設計方法與試驗或有限元素分析結果差距在12%之內，旋轉勁度Kg 之差距則在23%內。本研究利用習見軸力及彎矩互制公式推算出隅板之未折減塑性彎矩Mp,g，並與試驗以及有限元素分析結果比較後確認其準確性。本研究提出一套完整的CBF隅板設計流程。

關鍵字

同心斜撐(CBF) ； 雙WT銲接型 ； 隅板 ； 挫屈強度 ； Whitmore等效面積 ； 邊緣加勁板 ； 塑性彎矩容量 ； 旋轉勁度 ； 有限元素模型分析

並列摘要

Concentrically Braced Frame (CBF) is one of the widely used seismic systems in steel structures. Its inelastic lateral response relies on the brace members, gusset plates, beams and columns. The primary resistance to earthquake and wind lateral forces is from the brace members. CBFs offer high construction efficiency and allow reduced sizes or weights of beams and columns, thereby enhancing the overall cost-effectiveness of the structural system. Moreover, regardless of the shape of braces, gusset plates are always needed to connect them to the structural frame, marking the behavior of the gusset plates very important to the performance of the entire structural system. The compressive buckling resistance of the gusset plates directly affects the seismic performance of the braces. This combined analytical and experimental study incorporates the brace to investigate the gusset buckling and out-of-pane bending capacities of welded double-WT brace-to-gusset connections. The objectives include providing practical design recommendations for the calculations of gusset compressive buckling strength and out-of-plane bending capacity. Finite element model analyses were conducted first on practical double-WT brace-to-gusset connection assemblies to study the compressive buckling strength, plastic moment capacity, and rotational stiffness of the gusset plates. In order to validate the proposed design method, two sets of experiments on eight specimens were conducted to investigate the gusset buckling and bending behaviors, respectively. Five specimens with varying gusset plate thicknesses, shapes, sizes, with or without the edge stiffener were compressed to develop the buckling of gusset plates. The other three specimens were compressed using different eccentricities with or without gusset edge stiffener to develop the plastic moment of gusset plates. Experimental and numerical results show that using the proposed 45° angle of expansion in calculating the effective gusset width and an effective length factor K value of 1.3 for unstiffened gusset, and 1.0 for single-sided stiffened gusset can be considered. This will result in calculating inelastic compressive buckling strength with an error less than 7% compared to the test or finite element model analysis results. For a more convenient and conservative design approach, the expansion angle can also be considered as 37°. From the test and numerical results, it appears that increasing the gusset plate thickness directly is more cost-effective in enhancing the buckling strength than adding edge stiffeners when the material and construction costs is considered. Based on the experimental and numerical results, it is confirmed that the yield lines of the gusset plate can be connected at a distance of two times the gusset thickness, 2tg from the end of the brace. Applying the theoretical plastic axial vs. bending relationship, the analytical out-of-plane plastic moment capacity of the gusset Mp,g can be calculated with an error less than 12% when it is compared to the test and finite element model analysis results, while the analytical rotational stiffness of the gusset Kg has an error less than 23%.

並列關鍵字

Concentrically braced frame (CBF) ； Double-WT brace ； Gusset plate ； Buckling strength ； Whitmore effective area ； Edge stiffener ； Plastic moment capacity ； Rotational stiffness ； Finite element model analysis

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