Design of stainless steel SHS and RHS columns in fire by GMNIA with strain limits

A new fire design method by Geometrically and Materially Nonlinear Analysis with Imperfections (GMNIA) and using strain limits is proposed for stainless steel columns in this paper. In the proposed design method, owing to their computational efficiency, beam finite elements are employed to carry out the GMNIA of stainless steel columns in fire whereby the material strength and stiffness deterioration at elevated temperatures, the spread of plasticity, global instability effects, indirect fire actions and thermal expansion are directly taken into account. Due to the inability of beam finite elements to consider local buckling effects, the use of strain limits determined based on a modified continuous strength method (CSM) is proposed to capture the deleterious influence of the local instability effects on the structural resistances of stainless steel columns in fire. The ultimate capacity of a stainless steel column in fire is determined by (i) the temperature level at which the CSM strain limit is attained or (ii) the critical temperature at which the column is no longer able to carry the applied initial room temperature loading, whichever occurs first. In this study, stainless steel square hollow section (SHS) and rectangular hollow section (RHS) columns with and without axial and/or rotational end-restraints are taken into consideration. The capacity predictions obtained using the proposed design method are extensively verified against the benchmark results from shell finite element modelling and also compared against the predictions from the European structural steel fire design standard EN 1993–1-2. •A new advanced fire design method for stainless steel SHS and RHS columns based on GMNIA with strain limits is proposed.•Extensive numerical parametric studies are carried out, considering 2268 stainless steel SHS and RHS columns in fire.•Accuracy, safety and reliability of the proposed fire design method for stainless steel SHS and RHS columns are verified.•The proposed fire design method leads to more accurate and reliable ultimate resistance predictions relative to EN 1993-1-2 provisions.•The proposed method leads to an advanced and streamlined fire design, directly providing the failure temperatures and failure modes.