For slender steel components under uniaxial bending stress, verification against lateral torsional buckling must be provided in steel construction. This failure case of stability is decisive for the determination of sufficient load capacities for slender beams. The existing verification concepts for lateral torsional buckling point to a derivation from the approaches for the flexural buckling stability case. While verification with “reduction factors” has been available for flexural buckling for around 70 to 80 years, approaches to lateral torsional buckling have been included in a German standard (DIN 18800-2) for the first time since 1990. Since there is a different structural behaviour during lateral torsional buckling, a derivation based on the flexural buckling does not seem to make much sense. The key is therefore to analyze the deviating structural behavior and to improve the dimensioning of beams prone to lateral torsional buckling.
Within the scope of this project, a detailed determination of the load capacities of double-symmetrical steel girders under uniaxial bending stress is carried out. The structural behaviour is analyzed for various, specifically selected structural systems (single-span beams, cantilever beams and double-span beams). Limits of application of existing approaches for the determination of load capacities are determined. Parametric studies based on the yield zone theory serve as the basis for the analysis. A new combined approach of pre-rotation and pre-deformation for the geometric imperfections in yield zone calculations affine to the eigen shape is derived. Based on a comparison of the load capacities, system and profile-dependent scatter of the load capacities are shown and determined quantitatively. Parameters, such as the relative slenderness ratio and the ratio of the cross-sectional values Iy / IT, are identified, varied and analyzed in detail with regard to their influence on the load capacities. These load capacities are used to determine load capacities for each basic system depending on the relative slenderness and cross-section in the form of mathematically required reduction factors and necessary imperfections for the replacement imperfection process. A detailed identification of the decisive failure cases and investigations into the respective main areas of application takes place.
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