Experimental analysis of built-up closed cold-formed steel columns with restrained thermal elongation under fire conditions

An experimental research on the fire behaviour of compressed cold-formed steel columns with closed built-up cross-sections and restrained thermal elongation is presented. Several parameters were assessed, including the influence of loading level, boundary conditions, restraint to thermal elongation imposed by the surrounding structure and cross-sectional shape. The investigation suggests that an increase in the non-dimensional axial restraint ratio and column load levels lead to a decrease in critical temperatures. Furthermore, the 350 °C critical temperature limit predicted in the EN 1993-1-3:2005 may be too simplistic and conservative for fire design of this type of columns.