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

Abstract

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 thermal-stress 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.