Elastic distortional buckling stress of corroded C-section steel members under bending

The elastic distortional buckling stress, which is calculated by classic analytical model with uniform cross-sectional thickness, is unsuitable for evaluating the bearing capacity of flexural members with uneven corrosion using the direct strength method directly. Therefore, based on the energy approach, a modified flange-lip model which involved uneven residual thickness distribution along the length direction of flange and lip, was proposed for the distortional buckling stress evaluation to a corroded flexural C-section member. Corrosion effects on two key parameters in this model, namely buckling half-wave length and rotation spring stiffness, were also considered. Four-point bending tests of eight pairs of corroded C-section steel members under distortional buckling were carried out to validate the accuracy of the analytical model. Using the direct strength method, the ultimate loads of test members were converted into elastic distortional buckling stresses, which were then compared with the buckling stresses calculated from the corresponding analytical models. The comparison results show that the elastic distortional buckling stresses calculated from tests and analytical models have errors within 10 %, confirming the accuracy of the analytical model. Parameter studies indicate that the corrosion effect on webs dominates the buckling half-wave length and rotational stiffness compared to that on compression flanges and lips. However, this effect results in a decreasing trend for the buckling half-wave length and an increasing trend for rotational stiffness with higher corrosion ratios. Corrosion on the compression flange leads to a slight increase in elastic distortional buckling stress, whereas corrosion on the web and compression lip has the opposite effect of decreasing it.