Global buckling of S690 transversely-stiffened plate girders with slender webs: Behaviour and design

High-strength steels (HSSs) are now used globally in different structural applications because of their constructional and environmental merits. Though, investigations on HSS elements are still relatively limited. Herein, the lateral-torsional buckling (LTB) response of laterally-unsupported plate girders with stiffened slender webs is explored considering steel S690, which is currently under extensive testing worldwide. This is done by the finite element (FE) modelling to provide numerical models that well simulate their actual behaviour. Accordingly, FE models are verified first through comparisons with available tests in the literature. After that, parametric analyses are generated to examine the effects of the geometrical characteristics of the cross-section (in terms of the effective radius of gyration for LTB (rT) and the elastic section modulus referred to compression flange (Sxc)) and the laterally-unsupported length on the behaviour and strength of these girders. The results show that by increasing the value of rT, computed as the radius of gyration about the minor-axis of the compression flange plus one-sixth of the web, the strength of the girders increase more efficiently compared with the relative increase in rT. On the other hand, while increasing the value of the section modulus Sxc is found to raise the strength of the girders, the increase in the strength has been relatively found to be less than the increase in the value of Sxc. Additionally, based on the current results, the girder slenderness parameter of 2.0 is found as the inelastic LTB limit of such girders built up with S690, from which the girders of larger slenderness become ineffective and better to be made of conventional normal-strength steels. Furthermore, the bending strengths are compared with the design models given by AISC, EC3-1-1 and AS4100. The results show that they provide highly conservative results, with the predictions of AS4100 yielding the best design values. However, enhancements to the design models are still possible to provide lighter girders under the same applied loads. Accordingly, EC3 general design model (provided in Clause 6.3.2.2) is modified by using buckling curve “a" instead of buckling curve “d".