EN 1993-1-1 gives stability design rules for columns, beams and beam–columns up to S460, whereas EN 1993-1-12 gives additional guidance for S500 up to S700. Recent studies show that high strength steel members may be designed using improved buckling curves, where the enhanced behaviour is usually attributed to the improved material properties but mainly due to the more favourable residual stress distribution. The behaviour of unrestrained beams in HSS has not been widely studied. At present in EN 1993-1-1, the design rules for lateral-torsional buckling of beams are not dependent on the steel grade, meaning that the code does not distinguish between beams in conventional strength steel or HSS. In pursuit of an answer to the mentioned shortcomings, the present research is based on the experimental programme covering 12 full-scale tests, residual stress measurements, advanced numerical models and analytical derivations. The experiments cover different steel grades up to S690, welded and hot-rolled sections, homogeneous and hybrid (flanges in HSS and web in mild steel), double and mono-symmetric sections as well as variations in the cross-section class.

This paper provides an overview of the experimental programme, discusses the results for lateral-torsional buckling of beams, and presents an advanced numerical model that was calibrated to the experimental results including the measured residual stress distribution and geometrical properties of the members. The numerical model was explored to assess various assumptions for the member imperfections, and these are further compared with code recommendations.

EN 1993-1-1给出了直至S460的柱，梁和梁柱的稳定性设计规则，而EN 1993-1-12给出了至S700的S500的附加指南。最近的研究表明，可以使用改进的屈曲曲线来设计高强度钢构件，其中屈曲行为通常归因于材料性能的改善，但主要归因于更有利的残余应力分布。HSS中无约束梁的行为尚未得到广泛研究。目前，在EN 1993-1-1中，梁的横向扭转屈曲的设计规则不取决于钢种，这意味着该规范不区分常规强度钢或HSS中的梁。为了解决上述缺点，本研究基于涵盖12个全面测试的实验程序，残余应力测量，高级数值模型和分析推导。实验涵盖了高达S690的不同等级钢，焊接和热轧截面，均质和混合（HSS的法兰和低碳钢的腹板），双重和单对称截面以及横截面类别的变化。

本文提供了实验程序的概述，讨论了梁的横向扭转屈曲的结果，并提出了一种先进的数值模型，该模型已根据实验结果进行了校准，包括测得的残余应力分布和构件的几何特性。探索了数值模型以评估关于成员缺陷的各种假设，并将这些假设进一步与代码建议进行比较。