Flexural behaviour of hybrid high-strength steel I-beams

This paper presents a comprehensive numerical investigation into the flexural behaviour of hybrid high-strength steel (HSS) I-beams subjected to major axis bending. Initially, finite element (FE) models were developed and validated against available experimental results for welded homogeneous and hybrid HSS I-beams, employing a methodology consistent with prior research. These validated FE models were subsequently employed for parametric studies, covering a broad range of cross sectional slenderness for hybrid HSS I-beams. The results from FE models reveal that, to meet rotation capacity requirements, more stringent Class 1 slenderness limits for both the outstand flange in compression and the internal web in bending are necessary. Further, slenderness limits are proposed to facilitate plastic design of hybrid HSS sections under bending. Furthermore, comparisons between Class 2 and Class 3 slenderness limits and the codified European standards, revealed inadequacies for hybrid HSS beams. Consequently, new limits are recommended for classifying various cross-sections. Additionally, the applicability of the design equations in Eurocode (EN 1993-1-1), Direct Strength Method (DSM), and Continuous Strength Method (CSM) for hybrid HSS I-beams has been assessed, demonstrating increased variability. Hence, modified DSM and CSM formulations specifically tailored for hybrid HSS I-beams are proposed. The proposed equations are found to provide conservative and reliable predictions, thus recommended for inclusion in design standards.