Global buckling analysis of IFC-protected steel members with irregular sections under fire

Intumescent fire coating (IFC) is currently the major passive protection of steel structures under fire. However, the buckling behavior of IFC-protected steel members with irregular sections under fire has not been systematically quantified in existing studies. The high cost of fire tests and the cumbersome nature of coupled thermalstress analysis hinder extensive research on these members. This study proposes an improved algorithm to analyze the global buckling behavior of IFC-protected steel members with irregular sections under fire. The temperature field is calculated using a refined finite-element-based heat transfer analysis method that accounts for the equivalent thermal conductivity of IFC. Based on the temperature field, a cross-section analysis algorithm is proposed to determine the cross-sectional properties of the members, incorporating warping and Wagner effects due to the thermal gradients. The proposed thermal deterioration triangle element can reduce the error in calculating the cross-sectional properties by up to 3.98 % compared to traditional method while achieving higher efficiency. Parametric studies, comprising a total of 3168 analyses, reveal that fire exposure time, dry film thickness and section factor are the primary influencing factors. By summarizing the fire exposure times corresponding to 20 % and 80 % reductions in buckling capacity, an approximate evaluation equation is provided. Moreover, the proposed approach is integrated into a new software MSASect2 to offer a user-friendly tool.