交錨型雙核心自復位斜撐及核心更換型挫屈束制斜撐之耐震行為

Abstract

預力型自復位斜撐(SCB)是利用斜撐中的拉力構件束制斜撐中的鋼受壓構件，並在斜撐受軸拉與受軸壓下提供自復位能力，即在大變形下有回到零殘餘變形的能力。在拉力構件相同應變下，傳統雙核心自復位斜撐變形量可達兩倍傳統單核心自復位斜撐變形量(或是在相同斜撐變形量下，拉力構件額外應變減少一半)，有效降低拉力構件彈性應變需求。核心更換型挫屈束制斜撐(BRB)是利用高強度螺栓將兩組獨立的圍束單元夾合核心單元，使得斜撐受軸壓下不會挫屈而產生十分飽滿的遲滯消能行為。核心更換型挫屈束制斜撐只要移除圍束單元上的高強度螺栓，即可替換大地震下受損的核心單元而不需要重新製作圍束單元。本研究首次成功發展交錨型雙核心自復位斜撐，改變傳統雙核心自復位斜撐之各構件的斷面配置，使得外圍斷面尺寸有效減少，力學行為與傳統雙核心自復位斜撐相同，拉力構件所需施拉預力的數量僅需一半傳統雙核心自復位斜撐之拉力構件所需施拉預力的數量。本研究除了說明交錨型雙核心自復位斜撐力學理論外，並設計及試驗七組試體，分別為一組單核心自復位斜撐(長度7950 mm)、一組雙核心自復位斜撐(長度7930 mm)、一組交錨型雙核心自復位斜撐(長度7950 mm)及四組核心更換型挫屈束制斜撐(一組長度8010 mm和三組長度2570 mm)，三組自復位斜撐之拉力構件均使用D16 mm鋼鉸線，四組核心更換型挫屈束制斜撐均設計相同的螺栓間距、螺栓種類及整體挫屈強度對降伏強度的比值。本研究目的在於探討三組自復位斜撐的耐震行為，以及四組核心更換型挫屈束制斜撐對於有無滑動單元、圍束單元有無澆置無收縮水泥砂漿及近斷層地震歷時的影響。試驗結果顯示交錨型雙核心自復位斜撐之傳力機制與理論預測相符。第一階段試驗之層間側位移角2%時，單核心自復位斜撐之拉力構件由於鋼鉸線已經降伏而導致明顯的殘餘變形，其餘兩組自復位斜撐仍有良好的自復位行為。三組自復位斜撐的最大斜撐應變1.11%、1.11%與1.12%分別對應最大拉力構件應變1.36%、0.89%與0.77%及最大軸力1978 kN、1843 kN、1653 kN與1613 kN。四組核心更換型挫屈束制斜撐最大軸壓核心應變可達3.7-4.6%及最大軸壓力可達4133-4281 kN(=1.5-1.6倍降伏強度)，累積韌性容量可達616-1422，大於AISC(2010)耐震規範建議之200。本研究並利用非線性有限元素分析軟體ABAQUS模擬單核心自復位斜撐及交錨型雙核心自復位斜撐試驗行為，有限元素分析顯示與試驗結果及理論預測相符，證明交錨型雙核心自復位斜撐可利用非線性有限元素分析軟體ABAQUS進行參數研究。

Self-Centering Brace (SCB) uses tendons to constrain steel compression member of the brace and provides self-centering properties under brace in tension and compression that is restored to zero residual deformation. Conventional dual-core SCB is two times brace deformation capacity than conventional single-core SCB under same strain of tendons (or reduce to half the additional strain of tendons under same brace deformation capacity) that effectively reduce the elastic strain demand of tendons. Sandwiched Buckling-Restrained Brace (BRB) uses two identical restraining members that sandwich the core plate with fully tensioned high-strength bolts to prevent core buckling and have stable hysteretic response. Since two restraining members can be disassembled easily by removing the bolts, a damaged steel core can be replaced after a large earthquake. Thus, manufacturing new restraining members is not required, saving re-construction cost. This study is the first to successfully develop Cross-Anchored Dual-Core SCB that change the sectional configuration of each member of conventional Dual-Core SCB. Cross-Anchored Dual-Core effectively reduce the outer section size and half the number of applied pre-tension force to tendons compared to conventional Dual-Core SCB. In addition to explained the mechanical theory of Cross-Anchored Dual-Core SCB, this study designed and tested seven specimens, one Single-Core SCB (7950 mm long), one Dual-Core SCB (7930 mm long), one Cross-Anchored Dual-Core SCB (7950 mm long), four Sandwiched BRBs (the one is 8010 mm long and the other three are same 2570 mm long), tendons of three SCBs used same D16 mm steel strand, four BRBs designed same bolt spacing, bolt type, and ratio of global buckling strength to yield strength. The objective was to compare the seismic performance of three SCBs and study the effects of bonded material, concrete infill in the BRB and near-field loading for four BRBs. Test results indicate that the mechanism of Cross-Anchored Dual-Core SCB is consistent with prediction. Under drift 2% of phase 1 test, due to tendons yielding of Single-Core SCB resulting in large residual deformation, but the other two SCBs maintained good hysteretic response in self-centering behavior with no pre-tension force loss. Maximum brace strain of three SCBs were 1.11%, 1.11% and 1.12% corresponding to maximum tendons strain 1.36%, 0.89% and 0.77% and maximum load 1978 kN, 1843 kN and 1653 kN, respectively. Four BRBs with sufficient flexural rigidity of the restraining member can develop stable hysteretic responses up to a maximum core axial strain 3.7-4.6%, maximum compressive load 4133-4281 kN (=1.5-1.6 times the actual yield load), and cumulative plastic ductility 616-1422 that is much higher than that specified the value of 200 in AISC seismic provisions (2010). This work also uses the finite element software ABAQUS to analyze the test behavior of Single-Core SCB and Cross-Anchored Dual-Core SCB and compare with the test results and predictions which are proved similar. The analysis results shows Cross-Anchored Dual-Core SCB can use ABAQUS software to do parametric study.