Behaviour of cold-formed steel plain channels under axial and eccentric compressive loads

Abstract

Cold-formed steel sections are predominantly used in modern steel construction, because of their high strength to weight ratio. The main objective of this study is to investigate the behaviour of cold-formed steel plain channel sections subjected to axial and eccentric compression. Four different slenderness ratios were considered for plain channel sections with six cross sections. The effect of eccentricity on the load carrying capacity was studied theoretically, analytically and also experimentally. In the first phase, experimental investigations were carried out to study the behaviour of cold-formed steel plain channels. Two cross sections of size CFC 150x50x2 mm and CFC 200x50x2 mm were chosen for the study with a slenderness ratio of 40. The end conditions of the columns were chosen as fixed- fixed. The eccentricity chosen were 40 mm on the positive and 40mm on negative axis. Five tests were conducted and validated with the numerical study. All the specimens were tested until their failure. The effect of slenderness ratio, the effect of flat width to thickness ratio and the effect of eccentricity on the load carrying capacity were studied. The load versus axial shortening behaviour, the load versus strain behaviour and the load versus lateral deflection behaviour under the elastic as well as in the plastic ranges of loading were studied. The ultimate load carrying capacity of axially loaded plain channel obtained from tests was found to be twice compared to the section loaded with 40mm positive eccentricity. The initial stiffness decreased drastically for specimens with slenderness ratio 40 and beyond this slenderness ratio up to 120 the drop in initial stiffness was marginal. For the concentrically loaded specimens, the contribution of web element to the load carrying capacity was nine times higher than that of eccentrically loaded specimens. Specimens loaded through centroid and through positive eccentricity, failed due to interaction of flexural and local buckling.