Interaction among Flexural, Local, and Out-of-Plane Bucklings in Hysteretic Behavior of Steel Braces

本研究的目的是量化钢支撑的迟滞特性，包括弯曲、局部和面外屈曲之间的相互作用。为了获得这些特性的基本信息，进行了一系列的准静态加载试验，并通过实验结果与分析结果的比较，检验了解析解的准确性和局限性。在试验中，选择了两种宽厚比（用于考察局部屈曲的影响）、两种截面（宽法兰和窄法兰截面）、四种长细比（用于考察屈曲后范围内的强度劣化）和两种偏心比。试验结果表明：(a)窄翼缘截面的面内变形和面外变形都很显著，而宽翼缘截面的面内变形在小变形中占主导地位，中等变形时面外变形增加，大变形时面内变形再次增加；(b)当长细比较大时，面外变形（包括显著扭转）更为明显；(c)局部变形增大导致支撑断裂时间较短，延性较小；(d)断裂量与累积塑性应变之间存在较强的相关性。试验与分析结果的对比表明，该分析可以合理地估计出屈曲后最大强度和强度退化，并且可以追踪到面内变形占主导地位时的滞回特性，但无法追踪到面外变形较大时支撑的滞回特性。

The goal of this study is to quantify the hysteretic characteristics of steel braces that involve interaction among flexural, local, and out-of-plane bucklings. To obtain basic information on these characteristics a series of quasi-static loading tests were carried out, and accuracy and limitation of analytic solutions were examined through comparison between the experimental and analytical results. In the tests, two width-to-thickness ratios (to examine the effect of local buckling), two cross-sections (wide-flange and narrow-flange sections), four slenderness ratios (to examine the strength deterioration in the post-buckling range), and two ratios of eccentricity were chosen. It was found from the tests that (a) both in-plane and out-of-plane deformations were notable for narrow-flange sections, whereas for wide-flange sections, in-plane deformation was dominant in small deformations, out-of-plane deformation grew in medium magnitudes of deformation, and again in-plane deformation promoted in large deformations ; (b) out-of-plane deformation including significant torsion was more pronounced for larger slenderness ratios ; (c) shorter braces broke earlier (with smaller ductility) due to the growth of local deformation ; and (d) strong correlation was observed between the breakage and cumulative plastic strain. Comparison between the test and analysis revealed that both the maximum strength and strength degradation in the post-buckling range can be estimated reasonably by the analysis, and the analysis can trace the hysteresis when in-plane deformation dominates, but the analysis fails in tracing the hysteretic behavior of braces in which out-of-plane deformation is large.