具強化骨架之三層樓SCBF縮尺試體試驗

Abstract

同心斜撐構架（Special Concentrically Braced Frame，SCBF）為常見結構系統，但其常見破壞模式為低矮樓層斜撐受較大地震力影響後發生挫屈、降伏時，則該層樓的側向勁度則會降低，此後構架若受地震力影響繼續產生樓層位移，也會集中於該層造成破壞，此為結構的弱層(Soft Story)破壞模式，本研究為了改善同心斜撐構架的弱層情形發生，在原本的構架外增加一強化骨架，使其樓層變位能夠更均勻，以改善弱層情形。 研究方法為挑選三組適合實驗的三組試體來進行靜態往覆加載，其中一、二組試體為含強化骨架的縮尺三層樓同心斜撐構架其命名分別為試體S73、試體S42，第三組試體則為縮尺三層樓同心斜撐構架將命名為試體S0，不同的試體其位移集中參數(Drift Concentration Factor，DCF)將因強化骨架的特性不同而異，DCF可用以判斷強化骨架的改善效果。而強化骨架的設計參數採用勁度因子(α)和強度因子(β)來定義，如此三組試體的實驗行為可探討在不同α和β係數下的強化骨架對於只有單純同心斜撐構架的弱層改善情形、樓層位移集中程度等，預期不同試體對於構架弱層改善程度應為試體S73>S42>S0，而量化的結果則需透過本研究加以探討。 研究結果顯示，試體S73其抑制弱層效果為最佳、三樓斜撐的挫屈表現也最為明顯，其位移集中參數為試體S0的百分之七十，可見試體S73對於位移集中程度的改善效果。而試體S42在抑制弱層、三樓斜撐的挫曲表現上皆遜於S73，其位移集中參數只有試體S0的百分之九十。同時實驗結果亦顯示當強化骨架勁度因子(α)較高的時候可以降低其樓層位移的最大值。

The typical damage modes of Special Concentrically Braced Frame (SCBF) are overall and local buckling of the braces. It is common that the damage concentrates at certain floor(s) instead of spreading over all floors. Once the damage occurs, the soft story mechanism will result in the failure of the whole system. In this study, we use an extra structure, strongback, to redistribute the nonlinear deformation of SCBF and activate more structural members to dissipate energy and thus avoid damage concentration and improve the seismic performance of SCBF. We tested one-third-scaled, three-story, double-story X SCBF specimens with static cyclic loading procedure. Three testd specimens are S73, S42 and S0, which represent different combinations of stiffness and strength factors α and β for strongbacks. Specimens S73 and S42 are the specimens with strongbacks and S0 is the specimen without strongback. Qualitatively, we can expect that different properties of strongback have different impacts on the drift concentration of SCBF. To quantify the trends, we conduct the tests and observe that the speciem with the stiffest and strongest strongback (S73) is more capable of redistributing its nonlinear deformation. Test results show that the deformation distribution of Specimen S73 is more uniform and more brace members in three stories perform nonlinearly. Comparing Drift Concentration Factor (DCF), which is the ratio of the maximum dirft ratio to the averge drift ratio, we can observe 30% and 10% improvement in Specimen S73 and S42, respecitively. This improvement increases the nonlinear demand of the third-story braces ad reduce that of the first-story braces where the demand used to be excessive. Therefore, postpone the rupture of the first-story braces and enhance the ductility of the whole SCBF system.