Cold-formed steel built-up section beams are commonly employed in cold-formed steel framing owing to their excellent mechanical performance. In order to develop a simplified approach for obtaining the flexural moment capacity of built-up section beams, both experimental study and numerical analysis on the flexural behavior of cold-formed steel built-up I-section and box section beams under flexural load were carried out in this study. The I-section beams are assembled from two back-to-back cold-formed steel lipped channels, and the box section beams consist of a cold-formed steel plain channel overlapping a lipped channel. First, four-point bending tests were performed on 30 simply supported specimens having 10 different configurations, and the moment capacities and failure modes of built-up section beams at ultimate loads were investigated. The failure characteristics observed were the interaction of local and distortional buckling of the web and top flange for I-section beams and local buckling of the web and top flange in pure bending for box section beams. Then, finite element models were developed to simulate the tested specimens and validated against the experimental results in terms of the moment capacities and failure characteristics. Moreover, extensive parametric studies, including section height-to-width ratio and flange width-to-thickness ratio, were conducted with the validated numerical models to identify the key factors influencing built-up section beams. Finally, a simplified calculation method considering the reduction factor of the gross section modulus of the built-up section to predict the flexural moment capacities of cold-formed steel built-up I-section and box section beams was proposed.

中文翻译：

---

冷弯型钢组合截面梁抗弯弯矩承载力简化计算方法

冷弯型钢组合截面梁由于其优良的机械性能，常用于冷弯型钢框架中。为了开发一种获得组合截面梁抗弯弯矩承载力的简化方法，对冷弯型钢组合工字钢和箱形截面梁在弯曲载荷下的弯曲行为进行了试验研究和数值分析。在这项研究中。工字梁由两个背对背的冷弯型钢带边槽钢组装而成，箱形截面梁由冷弯型钢平槽和带边槽钢组成。首先，对10种不同构型的30个简支试件进行了四点弯曲试验，研究了组合截面梁在极限载荷下的弯矩承载力和破坏模式。观察到的破坏特征是腹板和上翼缘的局部和扭曲屈曲的相互作用，对于工字梁，腹板和上翼缘在纯弯曲中的箱形截面梁局部屈曲。然后，开发了有限元模型来模拟测试样本，并根据弯矩容量和失效特性的实验结果进行验证。此外，还使用经过验证的数值模型进行了广泛的参数研究，包括截面高宽比和翼缘宽厚比，以确定影响组合截面梁的关键因素。最后，