Structural fire robustness of edge steel columns with unsymmetrical bending moment in steel-framed structures

The structural fire design method presented in EN 1993–1–2 has been developed to provide a realistic prediction the fire resistance of isolated steel columns. However, this approach may result in columns with a limited safety margin, raising concerns about their reliability in fire when part of a sub-assembly and subjected to system effects not accounted for in Standard Fire test conditions. This research numerically assessed the structural fire performance of edge columns in sub-assemblies designed according to EN 1993–1–2, as well as using a proposed new limiting temperature design equation. The accuracy of the numerical simulation model for the columns in ABAQUS was first validated by comparing them with relevant experimental tests, considering the influence of steel beams and composite slabs. A comparative analysis of the simulation results showed that edge steel columns designed using the proposed limiting temperature equation achieved a higher safety margin (Capacity-to-Demand Ratio, CDR = 1.30) compared to those designed following the EN 1993–1–2 specifications (CDR = 1.12), which reflects the ratio between the simulated column failure time and the specified FRR. The simulation results indicated that edge columns designed according to EN 1993–1–2 may be unconservative in some cases, as evidenced by the premature failure of edge column in Edge-EN-90–1 sub-assembly, which occurred 6 min before reaching the specified 90-minute FRR. Moreover, edge columns with non-compact cross-sections performed slightly better under a non-unfirm fire compared to these exposed to uniform fire. • The EN 1993-1-2 fire design method is unconservative for edge columns with connected composite beams. • Edge columns performed slightly better under a non-unfirm fire compared to these exposed to uniform fire. • The edge steel column can maintain an adequate safety margin when designed using the proposed limiting temperature equation.