In cold-formed steel (CFS) structures, the application of back-to-back built-up channel beams is increasing steadily. The increasing demand of CFS sections as a cost-effective design solution has led to the development of CFS built-up sections. These sections take advantage of higher load-carrying capacities and may be used for longer beam spans. Applications include beam members in CFS wall studs, truss members and floor joists. In such an arrangement, the intermediate screw fasteners at discrete points along the length prevent the individual channel sections from buckling independently. However, limited experimental or finite element (FE) analyses have been reported in the literature for back-to-back built-up channel sections under four-point bending. Furthermore, there is limited investigation of the effect of screw spacing for flexural strength. This paper addressees this issue with 12 experimental test results. Two different cross-sections, referred to as BU75 and BU90, were considered with different screw spacings of 1900 mm, 950 mm and 475 mm. Initial geometric imperfections were measured prior to the bending tests. A nonlinear elasto-plastic FE model was then developed, the results of which showed good agreement against the experimental test results. Using the validated FE model, an extensive parametric study was conducted to investigate the effect of screw spacing on flexural strength of such back-to-back built-up CFS channel beams. In total, the results of 108 parametric analyses are reported. Both the experimental and FE results were compared against the design strengths calculated in accordance with the American Iron and Steel Institute (AISI) and Australian and New Zealand Standards (AS/NZS).

在冷弯型钢（CFS）结构中，背靠背组合式通道梁的应用稳步增长。CFS部分作为一种具有成本效益的设计解决方案的需求不断增长，导致了CFS组合部分的开发。这些部分利用了更高的承载能力，可用于更长的光束跨度。应用范围包括CFS墙钉中的梁构件，桁架构件和地板托梁。在这样的布置中，沿着长度的离散点处的中间螺钉紧固件防止各个通道部分独立地屈曲。但是，有限的实验或有限元（FE）分析已在文献中报道了四点弯曲下背靠背的组合通道截面。此外，螺钉间距对弯曲强度影响的研究很少。本文通过12个实验测试结果解决了这一问题。考虑了两个不同的横截面，分别称为BU75和BU90，其螺钉间距为1900 mm，950 mm和475 mm。在弯曲测试之前测量了初始几何缺陷。然后建立了非线性弹塑性有限元模型，其结果与实验测试结果吻合良好。使用经过验证的有限元模型，进行了广泛的参数研究，以研究螺钉间距对此类背靠背组合CFS通道梁的抗弯强度的影响。总共报告了108个参数分析的结果。