Fires in urban areas present a significant risk to human life, making it crucial to analyse the structural resistance of elements at high temperatures to prevent building collapse. Stainless steel, widely used in construction due to its durability and corrosion resistance, can experience mechanical property degradation under extreme temperatures, potentially leading to structural failure. This study aims to evaluate the fire resistance of stainless steel beams using numerical simulations based on the previously validated finite element model. By analysing different stainless steel grades and geometric configurations, this research seeks to provide insights that enhance the fire safety of stainless steel beams.
The study is based on numerical modelling of stainless steel beams subjected to fire conditions. This research uses ANSYS and validates the finite element model corresponding to the sample beam (B2) described by Fan et al. (2016). The simulations determined the load-bearing capacity, temperature distribution, and fire resistance time. Three groups of stainless steel grades (austenitic, ferritic, and duplex) were examined to compare their thermal and mechanical performance. The parametric analysis explored the influence of geometric dimensions, applying load levels of 0.2, 0.4, and 0.6 of the total load-bearing capacity to assess their impact on failure time and maximum critical temperature. This study also presents the results obtained from the simplified calculation method, assuming the same degree of utilisation, allowing us to determine the critical temperature and fire resistance time.
The numerical model demonstrated high accuracy in load-bearing analysis, with force-displacement results showing an average error of 3.97% compared to experimental data. However, temperature validation revealed that the numerical simulations predicted higher temperatures than experimental results, likely due to differences in thermal insulation applied at the top of the beams. During the fire resistance validation, the numerical model corresponding to sample B2 closely matched the experimental results, with a maximum Root Mean Square Error (RMSE) of 139 [°C] for position T2. This sample failed due to in-plane bending influenced by the presence of stiffeners. The parametric analysis revealed that austenitic steel 1.4301 had the lowest load-bearing capacity at room temperature, while duplex 1.4462 exhibited the highest, as expected due to its higher yield and ultimate stress, though it shows lower ductility. Austenitic and duplex steels behave similarly in thermal analysis, whereas ferritic stainless steel presents higher heat conduction, resembling carbon steel. The thickness and width of the cross-section have more influence on temperature distribution than the height of the cross-section, based on the three-sided fire exposure. Regarding fire resistance, the austenitic steel 1.4571 provided the longest resistance time due to its high nickel content, whereas ferritic 1.4016 exhibited the lowest fire performance. Among stainless steel grades, fire resistance is closely related to their atomic microstructure and chemical composition, particularly the presence of nickel and other alloying elements. Austenitic stainless steels, which have a higher percentage of nickel, generally exhibit superior fire resistance due to their stable face-centred cubic microstructure, which helps retain strength and ductility at elevated temperatures. Austenitic stainless steel, grade 1.4301, has at least 35% strength capacity at 800 °C (CEN, 2023; Farmani et al., 2021). The simplified results provided lower critical temperatures and fire resistance times for all cross-sections and material grades, with fewer exceptions, especially at high load-levels.
The conclusions of this research are only applicable to the stainless steel grades, sections under evaluation and the same expected failure modes.
This paper can be used to design different stainless steel beams, assuming different grades and RHS cross sections.
Safer and sustainable construction using stainless steel.
This study provides a comprehensive numerical evaluation of stainless steel beams under fire conditions, contributing valuable insights into the structural behaviour of different stainless steel grades. The research highlights the importance of material selection and geometric design in fire resistance, offering engineers and designers critical information for optimising structural safety. By validating numerical models with experimental data and exploring parametric variations, the study enhances the understanding of fire-resistant stainless steel elements, supporting the development of safer and more efficient building designs (cross-sections, load level and stainless steel grades). A new proposal relating to the maximum critical temperature determination and the load level is presented for all the steel grades and load levels.
