Residual Strength of Sigma-Shaped Cold-Formed Steel Stub Columns under Eccentric Compression after Fire Exposure

This study conducts numerical analyses of the postfire behavior of sigma-shaped cold-formed steel (CFS) stub columns subjected to eccentric loading by finite-element modeling (FEM). The reduction in strength reached 20.34% due to exposure to a temperature of 800°C, with longer columns (3,000 mm) exhibiting superior performance (12.51% decrease in strength) compared with shorter columns (1,800 mm). The screw spacing influenced fire resistance: a spacing of 100 mm resulted in an 18.25% reduction in strength, whereas spacings of 200 and 300 mm exhibited smaller decreases of 16.57% and 16.97%, respectively. Eccentric loading resulted in premature failure, with a strength reduction of 17.27% in the x-direction and 19.3% in the y-direction, whereas the influence of combined eccentricity was marginally exacerbated the degradation by an additional 0.33%. The failure modes transitioned from local buckling to flexural-torsional instability and inelastic deformation, with total strength reductions attaining 25.6% in extreme conditions. These results emphasize the need for improved design techniques to augment fire resistance and structural integrity in cold-formed steel applications.