Naturally buckling steel braces (NBBs) have been recently developed by the authors and co-workers to improve the buckling performance and energy dissipation capacity of braced framed structures. In NBBs, a low-yield-point steel (LYS) channel and a high-strength steel (HSS) channel are connected using steel battens to build up a dual-material steel section. An intentional eccentricity is introduced along the brace length to subject the brace to bending loads in addition to axial loads. Previous experiments have demonstrated that this combined axial-flexural response stabilizes the compression behaviour of the brace and enhances its tensile post-yielding stiffness through a novel deformation mechanism. In this paper, the cyclic behaviour of two full-scale NBB specimens with different section sizes and eccentricities are investigated experimentally. Gusset plate pin-connections that accommodate in-plane buckling are used to release the brace ends from high ductility demands. Two low-cycle fatigue protocols with increasing amplitudes and repeated inelastic loading cycles at the event of local buckling are adopted. Test results show that both NBB specimens exhibited a stable hysteresis behaviour by delaying the onset of local buckling up to a 1.5 % story drift ratio (SDR). Notably, the specimen with larger section and larger eccentricity provided a stable tensile strength under five repeated loading cycles of 2.0 % SDR. An equivalent damping ratio of 0.4 was measured. In addition to the experimental research, a computational study is performed with the aid of the finite element software ABAQUS to evaluate partially strengthening method of the sections against local buckling. It was found that the energy dissipation capacity of NBBs can be enhanced up to 40% by using rib stiffeners at critical locations, while the use of thicker channel battens can provide further restrain to local buckling growth up to a 3.0% SDR. The paper develops the physical equations to support an analytical hysteretic model for predicting the force-displacement cyclic relationship of chevron NBBs. The accuracy and targeted conservatism of the proposed hysteretic model is confirmed through comparisons with the test results.

作者和同事最近开发了自然屈曲的钢制支撑（NBB），以提高支撑框架结构的屈曲性能和能量消散能力。在NBB中，使用钢条连接低屈服点钢（LYS）通道和高强度钢（HSS）通道，以构建双材料钢型材。沿支架长度引入故意的偏心距，以使支架除了承受轴向载荷外还承受弯曲载荷。先前的实验表明，这种组合的轴向挠曲响应可通过新颖的变形机制稳定支撑的压缩行为，并增强其屈服后的刚度。本文通过实验研究了两个截面尺寸和偏心率不同的满刻度NBB标本的循环行为。角撑板的销钉连接可承受平面内的弯曲，用于将支架端部从高延展性要求中释放出来。在局部屈曲的情况下，采用了两种振幅增加和重复的非弹性加载循环的低周疲劳方案。测试结果表明，两个NBB样品均通过将局部屈曲的发生延迟到1.5％的故事漂移率（SDR）来表现出稳定的磁滞行为。值得注意的是，在2.0％SDR的五个重复加载循环下，具有较大截面和较大偏心率的样品提供了稳定的拉伸强度。测得的等效阻尼比为0.4。除实验研究外，还借助有限元软件ABAQUS进行了计算研究，以评估截面局部抗弯屈的方法。发现在关键位置使用肋骨加强筋可以将NBB的能量消散能力提高至40％，而使用较厚的通道板条则可以进一步抑制局部屈曲增长，直至SDR达到3.0％。本文开发了物理方程，以支持用于预测人字形NBB力-位移循环关系的分析滞后模型。通过与测试结果进行比较，确定了所提出的滞回模型的准确性和目标保守性。本文开发了物理方程，以支持用于预测人字形NBB力-位移循环关系的分析滞后模型。通过与测试结果进行比较，确定了所提出的滞回模型的准确性和目标保守性。本文开发了物理方程，以支持用于预测人字形NBB力-位移循环关系的分析滞后模型。通过与测试结果进行比较，确定了所提出的滞回模型的准确性和目标保守性。