A cross-section of cold-formed circular tube is easily deformed by the occurrence of local buckling under loads, which affects the collapse mechanism of the structure. However, few papers have been reported on the cross-sectional deformation of the tubular members. In this paper, axially loaded cold-formed circular tubes were subjected to a monotonic shear loading and the deformation mode of cross-sectional shape, and the cross-sectional deformation ratio of the cold-formed circular tubes in the axial direction at local buckling were clarified. In addition, the deformation mode in which the coefficient of the trigonometric function was assumed by employing the regression analysis and was suitable for experimental measurements.
