Optimal design of a structural member is a design process of selecting alternative forms to obtain its maximum strength while maintaining the same weight, leading to the most economical and efficient structure. Amongst steel structures, cold rolled steel ones can effectively gain this requirement as they are thin-walled structures that offer the high ratio of strength over weight. However, the design is very challenging as these members are prone to buckling and failure at low loads. In this paper, the buckling and ultimate strength of cold rolled channel sections was studied using numerical modelling. In order to improve the section strength, the development of various alternative cold rolled formed sections included additional bends such as intermediate stiffeners. The section strength was optimised through a practical approach which altered the stiffener's position and shape and searched for maximum buckling and ultimate strength under bending. In this approach, a nonlinear Finite Element model was first developed for an industrial channel beam subjected to four-point bending tests and this model was validated against experimental test data. The verified model was then used to conduct a parametric study in which the effects of a stiffener's properties on the section strength including its position, shape, size and material properties by the cold work at bends were investigated in detail. Several different cold rolled channel sections having intermediate stiffeners at web and flanges with and without the cold work effect on material properties at the stiffener's bends were considered for this investigation. In addition, a design method, the Direct Strength Method (DSM), was utilised to take into account the effects of a stiffener's properties on the section strength and results were compared with the Finite Element modelling results. It was found that some significant improvements were obtained for the section strength of the optimised sections in comparison to the original sections. An optimal shape for the channel section with maximum ultimate strength in distortional buckling could be obtained with both the stiffeners' position, shape, size and quantity, and the cold work effect. The cold work effect was found most significant in the cases of changing the width of the web stiffeners and the position of the flange stiffeners. It also revealed that, the currently available DSM beam design curve for distortional buckling provided good agreement in predicting buckling load and ultimate strength capacity for most of the considered sections with and without the cold work effect included; however, the DSM provided overestimate results compared to the Finite Element model results in the sections with web intermediate stiffeners, in particular, when the tip of web intermediate stiffener moved away from the web-flange junction in the horizontal direction.

结构构件的最佳设计是一种选择替代形式的设计过程，以在保持相同重量的同时获得最大强度，从而获得最经济，最有效的结构。在钢结构中，冷轧钢结构是薄壁结构，可以提供很高的强度重量比，因此可以有效地满足这一要求。但是，设计非常具有挑战性，因为这些构件在低负载下易于弯曲和失效。本文利用数值模型研究了冷轧槽钢的屈曲和极限强度。为了提高型材的强度，各种冷轧成形型材的开发都包括附加的弯头，例如中间加强筋。通过实用的方法优化了截面强度，该方法改变了加劲肋的位置和形状，并在弯曲时寻求最大的屈曲和极限强度。在这种方法中，首先针对经过四点弯曲测试的工业通道梁开发了非线性有限元模型，并针对实验测试数据对该模型进行了验证。然后，使用经过验证的模型进行参数研究，在其中详细研究了加劲肋特性对截面强度（包括其位置，形状，尺寸和材料特性）的影响，这些强度包括弯头处的冷作。几个不同的冷轧槽型材，在腹板和法兰处有中间加强筋，有无冷作对加强筋材料性能的影响 这项研究考虑了S型弯头。此外，采用一种设计方法，即直接强度方法（DSM）来考虑加劲肋特性对截面强度的影响，并将结果与​​有限元建模结果进行比较。发现与原始截面相比，优化截面的截面强度获得了一些显着的改善。通过加劲肋的位置，形状，大小和数量以及冷作效果，可以获得具有最大屈曲极限强度的通道截面的最佳形状。在改变腹板加劲肋的宽度和法兰加劲肋的位置的情况下，发现冷加工效果最为显着。这也表明，当前可获得的用于变形屈曲的DSM梁设计曲线在考虑和不包括冷作效应的情况下，在考虑的大多数截面中预测屈曲载荷和极限强度能力方面具有良好的一致性；但是，与有限元模型相比，DSM提供的结果高估了带有腹板中间加劲肋的部分，特别是当腹板中间加劲肋的尖端在水平方向上离开腹板-法兰连接处时。