Behaviour of cellular steel beams at ambient and high-temperature conditions

New developments in building construction have been observed to attain sustainable design criteria and the efficient use of raw materials, as steel is an example. This led to an increase in recent research on the optimization of geometric configurations of web-opening steel sections to meet cost-effectiveness in structural design. Improvement of the design method for perforated unrestrained steel beams to assess their behaviour under lateral torsional buckling (LTB) is still an ongoing issue for scientists and designers alike. In this article, cellular beams bound to instability were studied analytically by Eurocode and numerically by the finite element method to investigate their behaviour at ambient and elevated temperatures due to fire. The analysis encompasses the effect of the coupling and the endplates' thickness on the cellular beams' collapse strength considering the initial geometric imperfections and material nonlinearities. A parametric study including changing temperature, crosssection geometry, and web aperture configurations was done for beams subjected to uniform bending and distributed load. The analyses depicted the following failure modes: LTB and LTB+ plastification of the two Tsection (P-2 T) for end moment load and yielding of top tee section's flange (B-1 T), P-2 T, web post-buckling (WPB), Vierendeel mechanism (VM) and LTB for a distributed load. Combined failure modes such as LTB + WPB, LTB + VM and LTB + VM + WPB have also been observed. Buckling curves for cellular beams were assessed by comparing FE reduction factors with those of the buckling curve recommended by Eurocode 3 for equivalent solid steel beams. A new proposed formula for the plateau length of the LTB curves was obtained, based on the mean squared error method (MSE) between the numerical results and Eurocode formulae. The comparison between the numerical and the simplified design method predicted results shows that the proposed formulae have reduced the discrepancy and improved the LTB curve to better assess the cellular beams behaviour.

Automated summary

New developments in building construction have focused on achieving sustainable design and efficient use of raw materials, with steel being a key example. This has led to increased research on optimizing the geometric configurations of steel sections with web openings to ensure cost-effective structural design. The improvement of design methods for perforated steel beams to assess their behavior under lateral torsional buckling (LTB) remains a topic of ongoing interest for scientists and designers. This article investigates the behavior of cellular beams at ambient and elevated temperatures due to fire, through both analytical and numerical methods. The study evaluates the effect of coupling and endplate thickness on the collapse strength of the beams, considering geometric imperfections and material nonlinearities. Parametric studies were conducted, considering changing temperatures, cross-section geometries, and web aperture configurations, for beams subjected to uniform bending and distributed loads. The analyses revealed various failure modes, and a new formula for the plateau length of the LTB curves was proposed to better assess the behavior of cellular beams.