Comparative Numerical Assessment of Fire-Damaged Steel Connections Under Cyclic Loading

The residual cyclic performance of fire-damaged beam–column connections is critical when assessing the potential reuse, repair, or replacement of steel structures. This study presents a comparative numerical investigation of connections fabricated from SN400YB carbon steel and austenitic EN 1.4404, duplex EN 1.4462, and ferritic EN 1.4003 stainless steels. A three-dimensional finite element model was validated against published post-fire cyclic tests on SN400YB connections using experimentally reported residual material properties measured after the prescribed thermal exposure and natural-air cooling. The model achieved an average discrepancy of 3.93%, with maximum differences below 9%, providing a reliable basis for the subsequent comparative assessment. The validated framework was then extended to the stainless-steel cases using grade-specific residual post-fire properties together with representative cyclic plasticity parameters. By maintaining identical geometry, boundary conditions, and loading protocol, the study provides a consistent comparison of material- and temperature-dependent cyclic trends across the investigated grades. FE was used as the reference structural model, while Taguchi analysis quantified the relative influence of the investigated parameters and ANN provided a nonlinear surrogate representation of the FE response. Performance was assessed in terms of moment capacity, displacement ductility, hysteretic energy dissipation, and rupture index. Temperature was found to be the dominant parameter, whereas the investigated connection details had a secondary influence. Within the adopted numerical framework, EN 1.4462 exhibited the most favourable comparative response, while EN 1.4003 showed the greatest degradation at the higher exposure temperatures, providing comparative insight into the post-fire cyclic behaviour of the investigated steel grades.