Flexural-torsional buckling of high-strength steel beams

• Makes a case for research of lateral buckling of HSS, since this material is used increasingly in structural applications.
• Considers steels with yield strengths exceeding 690 MPa.
• Results show current buckling curves need modification because of different stress-strain law and residual stresses.

High-strength steel (HSS) is gaining widespread acceptance in contemporary engineering structures, with grades of up to 690 MPa being included in many design standards. However, although strength grades well in excess of 690 MPa are possible with modern metallurgical processes, these are not compliant with most design codes of practice. HSS is advantageous when strength, rather than stiffness, predominates the structural response. When this is the case, HSS is very useful in reducing the self-weight of the structure, as many be needed in structural modification, or in contriving a design that minimises the carbon footprint of the structure.Research on the flexural-torsional buckling of steel structures is extremely abundant in the literature, and guidance in codes is very comprehensive. It is known that the resistance to flexural-torsional buckling depends on the interaction of (i) elastic buckling; (ii) yielding and post-yielding and (iii) residual stresses. Current design curves are based on the elastic buckling resistance, which is modified to account for the yield and post-yield response of structural steel and the residual stresses in the cross-section. However, HSS with yield stresses exceeding 690 MPa have somewhat different yield and post-yield characteristics and significantly different patterns of residual stresses when compared with structural steel.This paper uses ABAQUS software to investigate the flexural-torsional buckling strength of HSS I-section beams, by incorporating the stress-strain curves and residual stresses measured experimentally and reported in the literature. With a similar methodology to structural steel members, the interaction of elastic buckling at the member level with the material characteristics at the cross-sectional level is investigated and a strength design formulation is proposed.