特殊同心斜撐構架之斜撐構材耐震性能

Abstract

特殊同心斜撐構架 (Special concentrically braced frame, SCBF) 於強震區域是一種可有效地抵抗地震力之構架系統。不同於一般的抗彎矩構架，SCBF的非彈性變形源自斜撐受軸拉力作用降伏和受壓產生整體或局部挫屈，斜撐構材力量則透過接合板傳遞至梁、柱桿件。 本研究之目的在建立H-型斷面斜撐與接合板之遲滯行為，探討其強度與遲滯迴圈。研究方法採用非線性之有限元素分析，建立數值模型，以接合板與斜撐構材之拉力強度比值 (βj) 、偏移區域長度 (LC) 與接合板有效寬度 (W) 等3組參數進行探討斜撐與接合板接合之非彈性行為；藉由有限元素分析之參數研究結果以規劃試驗計劃，設計6組試體，試體參數除分析採用參數外並包含偏移區域型式 (LC/EC)，以進行往復載重試驗，以探討接合板細節於遲滯行為之影響。 有限分析結果顯示，增大強度因子參數βj可促使斜撐整體挫屈強度與消散能量之提昇。參數LC則顯示2t之偏移區域長度已足夠提供斜撐端部之旋轉。接合板寬度 增大下，接合板受力面積增加，較不易有應力集中產生，又相對縮短斜撐長度，於整體強度有些許提昇。試驗結果顯示6組試體皆具穩定非線性行為與消散能量之能力，具線性與橢圓偏移之梯形接合板皆可穩定傳遞斜撐構材力量，其遲滯迴圈可達5%至6%弧度之層間變位角。試體之斜撐構材面外變形量可達斜撐構材長度15%，而接合板則可提供2.5%斜撐構材長度之面外變形量，然而H-型斜撐構材挫屈後強度衰減較劇。4組具橢圓偏移 (EC) 試體皆有接合銲道處之接合板產生局部開裂行為，但非脆性破壞，亦指出這些地方可能有著應力集中現象。 本研究所發展之梯形接合板經數值模型分析與實體載重試驗可知其已具備力量傳遞與提供斜撐構材端部凹折之能力，並可使斜撐構材於受擬地震力作用下產生受壓挫屈、受拉降伏行為，以穩定的消散地震能量，所提出之研究設計參數應可以作為接合板設計之指標。

Special concentrically braced frame (SCBF) is one of the effective earthquake-resisting frames used in the high seismic area. Unlike the moment-resisting frame, inelastic deformation of the SCBF originates from the braces which are designed to yield in axial tension and to buckle, globally or locally, in axial compression. The brace forces are transferred to the beam and column through gusset plates. The purpose of this study is to establish the hysteretic behavior of H-shaped section bracing member and the gusset plate, and to investigate the strength and hysteresis. Nonlinear finite element analyses were conducted, and numerical models were established to research the inelastic hysteretic behavior of the brace and connection to gusset plate, considering three parameters: the ratio of tensile strength of the gusset plate to brace (βj), the length of the clearance (LC), and the effective width of the gusset plate (W). According to parametric study results, an experimental program was planned to carry out the cyclic loading test to explore the effect of gusset plate details on the hysteretic behavior. Six specimens were designed to consider the parameter of the type of clearance (LC/EC) in addition to the parameters used in the analysis. The results of the finite element analysis demonstrated that increasing the parameter βj resulted in the increase in overall buckling strength and energy dissipation of the brace. The parameter LC showed that the clearance length 2t provided adequate rotational capacity for the brace end. Increasing the gusset plate width (W) led to the decrease of the stress concentration at the gusset plate due to larger loaded area at the gusset plate, and to enhance slightly the overall buckling strength of the brace caused by the shorter brace length. The test results showed that all six specimens possessed stable nonlinear behavior and energy dissipation. The trapezoidal gusset plate (TGP) with linear or elliptic clearance could transfer stably the brace forces to the beam and column, and the hysteresis loop could reach 5 to 6% rad. of the interstory drift angle. The out-of-plane deformation (OOPD) of the brace reached to 15% of the brace length while the gusset plate could provide the OOPD of 2.5% of the brace length. However, the strength of the H-shaped brace deteriorated significantly after buckled. Four specimens with elliptic clearance revealed local cracking, but not brittle failure, at the gusset plate near the welding zone which also pointed out the possible stress concentration. The trapezoidal gusset plate developed in this study can possess the force transfer and rotational capacity for the brace end which have been demonstrated by the numerical model analysis and cyclic loading tests. The gusset plate can enhance the brace to stably dissipate energy exerted from earthquake excitation, by developing brace behavior of yielding in axial tension and buckling in axial compression. The proposed design parameters can be used for designing the gusset plate.