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.
The Ministry of Higher Education and Scientific Research, MESRS, of
Algeria, is gratefully acknowledged for the PhD grant funding support:
ref. 714/PNE/Doctorant/Portugal/2019-2020.
