为研究冷弯薄壁型钢（CFS）拼合箱形截面柱的畸变屈曲性能，首先对9根C形截面柱、9根U形截面柱及21根由C形和U形拼合而成的箱形截面柱进行轴压试验研究和数值模拟分析，考察其屈曲模式特征和受力特性. 在此基础上，提出一组假设模型以研究螺钉间距对拼合箱形截面柱变形特征和极限承载力的影响规律及其与试件半波长之间的关系. 研究结果表明：1）不同螺钉间距的试件，畸变屈曲半波数量和半波长（λc）均不相同. 2）螺钉间距小于0.9λc时，箱形截面柱的承载力大于C形和U形柱的承载力之和，即1+1>2的拼合效应. 3）螺钉间距大于0.9λc时，箱形截面柱的承载力逐渐接近C形和U形柱的承载力之和，即1+1≈2. 为计算CFS拼合箱形截面柱的极限承载力，在美国规范中直接强度法的基础上提出了一种计算箱形截面柱畸变屈曲弹性临界荷载的方法，将计算的临界屈曲荷载用于直接强度法以得到拼合箱形截面柱的极限承载力，理论计算结果与试验及有限元结果均比较吻合，验证了本文提出方法的准确度和适用性.
In order to study the distortional buckling behavior of cold-formed steel（CFS） built-up box-section columns，firstly，9 C-section columns，9 U-section columns，and 21 built-up box-section columns composed of C-section and U-section were investigated by the axial compression tests and numerical simulation. The buckling characteristics and mechanical behaviors of the columns were investigated. On this basis，a set of hypothesis models were proposed to study the influence of screw spacing on the deformation，the ultimate capacity，and the relationship between the screw spacing and the half-wavelength（λc） of CFS built-up box-section columns. The results show that：1） The number and half-wavelength of distortion buckling are different for the specimens with different screw spacing. 2） When the screw spacing is less than 0.9λc，the ultimate capacities of built-up box-section columns are greater than the sum of the ultimate capacities of C-section and U-section columns，that is，the splicing effect of 1+1>2. 3） When the screw spacing is greater than 0.9λc，the ultimate capacity of the built-up box-section column is gradually close to the sum of the ultimate capacities of the C-section and U-section columns，i.e. 1+1≈2. In order to calculate the ultimate capacities of CFS built-up box-section columns，an approach to predict the elastic critical load of distortion buckling was proposed based on the direct strength method（DSM） in American code，and then the calculated results were applied to the DSM to obtain the ultimate capacity of CFS built-up box-section columns. The results obtained from the calculation method are in good agreement with the experimental and numerical simulation results，which suggests the accuracy and applicability of the proposed method in this paper.