長跨桁架圍束式挫屈束制支撐之研究

Long-Span Buckling-Restrained Braces using Truss-Confined Restrainers

10.6849/SE.202106_36(2).0001

陳雋(Chun Chen)；林昱成(Yu-Cheng Lin)；吳安傑(An-Chien Wu)；陳律安(Lu-An Chen)；蔡克銓(Keh-Chyuan Tsai)

挫屈束制支撐 ； 巨型斜撐 ； 桁架圍束單元 ； 撓曲剛度 ； 剪力剛度 ； 穩定性分析 ； buckling-restrained brace ； mega brace ； truss-confined restrainer ； flexural rigidity ； shear rigidity ； stability analysis

結構工程

36卷2期（2021 / 06 / 01）

5 - 50

繁體中文

跨越多樓層之挫屈束制支撐在高層建築結構中的抗震應用漸趨廣泛，桁架圍束式挫屈束制支撐（truss-confined buckling-restrained brace, TC-BRB）為較新型之BRB，TC-BRB於圍束鋼管外部再配置一桁架圍束系統，由任意數量、方向與尺寸之桁架構架所構成，並與圍束鋼管共組成圍束單元來提供所需之撓曲剛度；因此其圍束鋼管與內灌水泥砂漿的撓曲剛度與斷面需求得以大幅下降。當安裝為具長跨與高軸力容量之斜撐構件時，更得以發揮減少材料用量、自重及初始凹曲等優點。本研究提出一全新型TC-BRB，將桁架圍束系統之斷面高度由過去的等斷面改為沿BRB軸向變化，於跨中央最高並以正弦函數曲線向兩端漸縮，更有效率地使用材料並獲更優美之外觀。為使此新創型BRB方便實際工程應用，本研究建立穩定性理論模型與耐震設計方法並進行相關實驗與數值驗證。先提出桁架圍束系統等效撓曲剛度與剪力剛度計算方式，再建立穩定性理論模型。考量剪力效應計算TC-BRB之整體彈性撓曲挫屈強度（P_(cr)）；並再考量初始缺陷與材料非線性行為來計算整體挫屈破壞強度（P_(lim)）。本研究並藉ABAQUS有限元素模型分析進行數值驗證，結果顯示理論模型在圍束單元的P_(cr)計算上，誤差小於10％；而於整體TC-BRB的P_(cr)計算上，誤差更小於3％。為驗證理論並評估TC-BRB之實際遲滯消能行為，本研究第一階段設計並新造兩組具不同桁架圍束系統型態、1／5縮尺總長6.3米、100噸級之TC-BRB試體，利用國家地震工程研究中心多軸向試驗系統執行反覆加載試驗。理論模型考量殘餘應力的效應後，預測所得P_(lim)與試驗結果的誤差小於6％；實驗證實本研究所建理論模型於穩定性預測之準確性，更證實本研究所提之設計方法與檢核程序的可靠性。為觀察TC-BRB更嚴峻的耐震消能與穩定性表現，本研究第二階段再設計兩組TC-BRB試體並提高其整體穩定性容量，理論預測的P_(lim)與試驗所得結果兩者誤差小於7％，再次確認所提理論模型之準確性；本文提供TC-BRB之耐震設計流程與範例以供參考。

Long span buckling-restrained braces (BRBs) are getting popular for applications in seismic tall buildings. Recently, a novel type of BRB, namely the truss-confined BRB (TC-BRB) with a constant-depth truss built into the restrainerhas been investigated. The TC-BRB's restrainer is constructed by attaching an additional truss system composed of several steel open-web truss frames outside the central steel casing in order to develop the overall restraining rigidity. Thus, the cross-sectionof the central steel casing and the weight of the infilled mortar in the TC-BRB can be significantly reduced in comparison with the conventional BRBs. The initial crookedness caused by the BRBs' self-weight can also be reduced in the cases of long-span and large axial capacity BRB designs. This study investigates a new type of TC-BRB using a varying-depth truss system in the restrainers. This type of TC-BRB could save construction material and achieve the structural aesthetic more effectively than those using the constant-depth trusses. In this study, stability analytical model and seismic design procedures are developed and verified. Key mechanical properties including equivalent flexural rigidity and shear rigidity of the truss system are firstly presented. It is illustrated that the TC-BRBs' elastic flexural buckling strength (P_(cr)) can be satisfactorily computed by incorporating Timoshenko shear effect into the classical stability theory. TC-BRBs's buckling failure strength (P_(lim)) can be further computed by considering the initial imperfections and inelastic material property. Abaqus finite element model (FEM) analysis results indicate that the proposed analytical model can satisfactorily predict the restrainers' P_(cr) with errors less than 10%; and predict the TC-BRBs' P_(cr) with errors less than 3%. In the first phase experiment, two 1/5-scale TC-BRB specimens, each of 6.3m long with the 1016-kN nominal yield strength anda constant- or varying-depth truss design, were tested in NCREE. Cyclic test results confirm that the P_(lim) of the two TC-BRB specimens can be accurately predicted using the proposed analytical model with errors less than 6% when the effects of residual stresses in the truss members are considered. In the second phase experiment, two additional specimens were fabricated with significantly increased stability capacities. Cyclic test results show that the P_(lim) of these two specimens can also be accurately predicted with the errors less than 7%, further confirm the reliability of the proposed analytical model. The TC-BRBs' experimental performance also suggests that the proposed design procedures are generally conservative and practical. This study concludes with the recommendations, produres and examples on the seismic design of the proposed TC-BRBs using the constant- or varying-depth trussses.

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