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滞回特性，包括弯曲，局部和平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，并通过实验和分析结果之间的比较，检查的准确性和限制的解析解。在试验中，选择了两个宽厚比（以检查局部屈曲的影响）、两个横截面（宽翼缘和窄翼缘截面）、四个细长比（以检查屈曲后范围内的强度劣化）和两个偏心率。试验结果表明：（1）窄翼缘截面的面内变形和面外变形都很显著，而宽翼缘截面在小变形时以面内变形为主，在中等变形时面外变形增大，在大变形时面内变形也增大;（B）长细比越大，平面外变形（包括显著的扭转）越明显;（c）短支撑断裂越早（具有较小的延展性），由于局部变形的增长;和（d）观察到断裂和累积塑性应变之间的强相关性。试验结果与分析结果的对比表明，该分析方法能够合理地估计支撑的最大承载力和屈曲后的强度退化，能够跟踪平面内变形主导时的滞回特性，但不能跟踪平面外变形较大的支撑的滞回特性。

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.