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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. [ABSTRACT FROM AUTHOR]

This article presents a study on the impact of the screw location and the diaphragm effects on the buckling behavior of the simply supported C/Z-section purlins under wind uplift loadings. The diaphragm effects provided by the sheeting and the warping-torsional effect induced by load eccentricity are taken into account in the differential equations of the nonlinear twisting flexural-torsional model. The biaxial bending moments, bi-moments, as well as the flexural-torsional buckling load of the purlin can be numerically obtained with the proposed model. The global, local, and distortional buckling interaction behavior and the limit states capacities are formulated based on the modified Direct Strength Method. The effects of both the restraints provided by the sheeting and impact of the screw location on the mechanical performance of the purlins are evaluated with the proposed method. The relationship between the buckling load and rotational restraint stiffness is also provided. The proposed methodology will contribute to the assessment of buckling capacity of purlin-sheeting systems. [ABSTRACT FROM AUTHOR]