Axial compression bearing capacity test and numerical simulation of corroded cold-formed thin-walled C-section stub columns after high temperature

To investigate the axial compression behavior of corroded cold-formed thin-walled C-section stub columns under varying fire temperatures and cooling methods, a total of 63 specimens were prepared. Corrosion was simulated by neutral salt spray tests, fire exposure by high-temperature heating, and fire extinguishing by different cooling methods. Subsequently, the axial compression tests were performed, and finite element models were established in ABAQUS for parametric analysis. Finally, a modified direct strength method was proposed to evaluate the ultimate bearing capacity of corroded C-section columns after high-temperature exposure and cooling. The results indicate that when the fire temperature was lower than 600°C, the ultimate load capacity was primarily affected by the corrosion level. As fire temperature exceeded 600°C, the ultimate bearing capacity of the naturally cooled specimens decreased significantly, while that of water-cooled specimens increased significantly, but the ductility was greatly reduced. Based on the experimental results and finite element parametric analysis, the applicability of the conventional Direct Strength Method (DSM) was evaluated. Since the existing design formulas do not consider the combined effects of corrosion-high temperature, an improved DSM calculation method is proposed for the corroded C-shaped short columns after fire in this study. Binary nonlinear fitting was performed using the Levenberg-Marquardt algorithm on the relationship between the control parameters in the modified method calculation formula and the fire temperature and corrosion rate. The prediction formulas for the control parameters under the combined effect of corrosion and high temperature exposure were derived. The proposed framework provides a practical basis for post-fire residual-capacity assessment and strengthening decisions for deteriorated cold-formed steel members.