Parametric study on lateral distortional buckling of steel–concrete composite cellular beams with HPFRC slabs

Steel–concrete composite beams under negative bending are susceptible to lateral distortional buckling (LDB), a failure mode that is not yet fully understood, particularly in the case of cellular sections. This study investigates the influence of key geometric parameters of steel–concrete composite cellular beams with HPFRC slabs on the elastic critical moment and ultimate moment by means of finite element analysis. The results showed that increasing p/D₀, increasing slab thickness, and using of midspan stiffeners led to increases of up to 13.2%, 27.1%, and 160.3%, respectively, in the critical moment, and up to 9.7%, 17.5%, and 61.6%, respectively, in the ultimate moment. In contrast, increasing D₀/d and span length L caused reductions of up to 14.5% and 51.2% in the critical moment, and up to 10.0% and 23.3% in the ultimate moment, respectively. Increasing the steel grade raised the ultimate moment by up to 34.4%, due to the bottom flange plasticization combined with LDB. For D₀/d up to 0.9 combined with p/D₀ up to 1.3, at spans of 6 and 8 m, the numerical models tended to fail through a combination of LDB and web-post plasticization. The inclusion of stiffeners modified the LDB half-wave pattern and shifted the failure mode to a combination of LDB and bottom flange plasticization. Among the analytical procedures assessed, Dias et al. and Roik provided the closest predictions of the critical moment, with mean deviations of 23% and 27% and coefficients of variation of 12% and 11%, respectively. For the ultimate moment, NBR 8800:2008, NBR 8800:2024, and EN 1994–1–1:2024 showed good agreement with the numerical results, with mean deviations ranging from 14% to 22% when analytical critical moments were used, and below 5% when the numerical critical moment was adopted, with coefficients of variation not exceeding 5%.