This article focuses on the lateral-torsional buckling resistance of girders with slender, class 4 cross-sections with a research aim to check the accuracy of the design resistance model of EN1993-1-1 and EN1993-1-5 on the coupled instability of lateral-torsional buckling and local plate buckling resistances. The current Eurocode-based design method considers in the effective cross-sectional resistance calculation that yield strength is reached in the extreme fibre of the cross-section, and the reduction factor ( ρ p ) related to local plate buckling is calculated based on this assumption. However, if lateral-torsional buckling occurs, maximum stress in the web can be significantly smaller at the ultimate limit state which is not considered in the effective cross-sectional resistance calculation. On the other side, EN1993-1-1 proposes to consider the effective bending moment resistance in the relative slenderness calculation of lateral-torsional buckling, which is in contradiction with the general definition of the relative slenderness ratio ( λ ¯ LT ) , which should refer to the plastic resistance divided by the critical load of the structure. This article aims to check if the current Eurocode-based design rules need improvement and to check the effect of the above-mentioned specific issues on the calculated lateral-torsional buckling resistance. An extensive numerical research programme is executed to check and compare the lateral-torsional buckling resistance of class 3 (as reference) and class 4 cross-sections, and results are compared to Eurocode-based design models.

中文翻译：

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具有 4 级腹板的梁的横向扭转屈曲：基于 EC3 的设计方法中耦合不稳定性的调查

本文重点研究细长4级梁的抗侧扭屈曲抗力，旨在检验EN1993-1-1和EN1993-1-5设计抗力模型对梁耦合失稳的准确性。横向扭转屈曲和局部板屈曲阻力。当前基于欧洲规范的设计方法在有效截面抗力计算中考虑在截面的极端纤维处达到屈服强度，并基于此假设计算与局部板屈曲相关的折减系数（ρ p ） . 但是，如果发生横向扭转屈曲，则在有效横截面阻力计算中未考虑的极限状态下，腹板中的最大应力可能会显着减小。另一方面，EN1993-1-1提出在横向扭转屈曲的相对长细度计算中考虑有效弯矩阻力，这与相对长细比( λ ¯ LT )的一般定义相矛盾，后者应指塑性阻力除以结构的临界载荷。本文旨在检查当前基于欧洲规范的设计规则是否需要改进，并检查上述特定问题对计算的横向扭转屈曲阻力的影响。执行广泛的数值研究程序来检查和比较 3 级（作为参考）和 4 级横截面的横向扭转屈曲阻力，并将结果与​​基于欧洲规范的设计模型进行比较。