The overall objective of the present study is to investigate the newlinebehaviour of cold-formed steel columns with and without concrete infill with newlinerespect to strength, cross-sectional shape, slenderness ratio, flat newlinewidth/diameter to thickness ratio and concrete core strength. The present study newlineis divided into three distinct phases of experimental investigation. In each of newlinethem, axial capacities with respect to various International codes of practice newlineand available design methods are compared with experimental results. A total newlineof sixty results of current tests and a total of twenty six results of experiments newlineconducted by previous researchers, available in the literature have been newlineconsidered. newlineIn the first phase, the behaviour of cold-formed steel circular and newlinesquare columns with and without concrete infill was studied. Experiments newlinewere conducted on thirty six numbers of cold-formed steel columns. Twenty newlinefour of which with concrete infill were tested and compared with identical newlinebare steel columns. The columns have been tested under axial compression till newlinefailure. The parameters considered were slenderness ratio of column and newlineconcrete core strength. The slenderness ratio was varied as 2, 4, 6, 8, 10, and newline12. M30 and M60 grade concrete were used as infill. The flat width/diameter newlineto thickness ratio was kept as 45. The load versus axial strain behaviour was newlinestudied. The failure modes were also observed. The effect of slenderness ratio, newlineconcrete filling and concrete confinement on strength of columns was studied.%%%