Biege‐ und Biegedrillknicken in konsistentem Ansatz als Basis einer allgemeinen Knickkurve für EC3‐1‐1, 6.3.4

Consistent approach for flexural and lateral torsional buckling as basis for a general buckling curve for EC3‐1‐1, 6.3.4. Within the general method of chapter 6.3.4 of EN 1993‐1‐1, for the general case of lateral torsional buckling (i. e. LTB with combined moment and normal force), the buckling curves of the special cases of lateral torsional buckling (i. e. LTB only with moment or FB with normal force only) are to be used. This, with regard to slenderness and imperfections, produces inconsistencies leading to conflicts with the intended generality and finally to incorrect results. For the individually combined effect of the in‐plane actions M_y and N are causal for the out‐of‐plane instability. Thus the amplification factors α_cr and α_ult, the related slenderness λ and the imperfections to be assumed in the eigenmode are depending on the ratio of M_y and N. Having this in mind a general formulation of a buckling curve for LTB with combined moment and normal force can be achieved being consistent with those of the special cases. Thereby the insufficient rule for the choice of buckling curve of 6.3.4 can be replaced. In the following paper it is therefore shown, based on the Ayrton‐Perry‐format, how the imperfection values for flexural buckling acc. to EC3 can be transferred to lateral torsional buckling. The derivations are accompanied by comparative FE‐calculations.     

Das plastische Kippmoment gerader Träger mit I‐Querschnitt

Es wird gezeigt, wie einfach die Tragfähigkeit gerader I‐Träger mit doppel‐ oder einfachsymmetrischem Querschnitt beim Kippen (Biegedrillkippen) mit Hilfe des plastischen Drehwinkels des gedrückten Flansches in guter Übereinstimmung mit Versuchen an großen Probekörpern berechnet werden kann. The plastic moment of lateral buckling of straight girders with I‐section. It is shown how simply the moment capacity in lateral buckling of straight girders with bi‐ or mono‐symmetric crosssection can be predicted with help of the plastic hinge rotation of the compression flange in good coincidence with experiments on large specimens.     

Vollständige äquivalente Imperfektionsmethode für biege‐ und druckbeanspruchte Stahlträger

Overall imperfection method for flexure and compression steel beam‐columns. The principles and applications of the overall (global) imperfection method (OIM) for beam‐columns are presented in this paper. The buckling resistance of a beam‐column member is determined by the resistance of its critical cross‐section taking into account second‐order effect of the eigenform equivalent initial imperfection. The maximum amplitude of this initial imperfection, in the shape of elastic buckling mode, is determined from fundamental cases, which are simply fork supported members with uniform cross‐section under uniformly distributed normal force or bending moment. The standardized buckling resistance of the fundamental cases is based on theoretical and empirical background. The proposed global imperfection method is adequate for computer‐aided design method using advanced elastic beam‐column finite element method including the warping behavior of the cross section. The accuracy of the presented method is illustrated step‐by‐step with numerical examples.     

Biegedrillknicken von I‐Profilen mit und ohne Voute — Bemessungshilfen für den vereinfachten Nachweis (Teil 1)

Bei Rahmentragwerken werden in den hochbeanspruchten Ecken häufig Vouten angeordnet. Die statisch‐konstruktiven Vorteile gevouteter Stäbe können derzeit nur für wenige Sonderfälle effizient genutzt werden, da die für den Tragsicherheitsnachweis erforderlichen Angaben fehlen. Es werden Bemessungshilfen vorgestellt, mit deren Hilfe der Nachweis biegebeanspruchter Bauteile mit und ohne Vouten mittels Handrechnung geführt werden kann. Diese umfassen Hilfen zur Bestimmung des idealen Biegedrillknickmoments und Empfehlungen bezüglich der Wahl einer geeigneten Traglastabminderungskurve. Abschließend werden die vorgestellten Bemessungshilfen anhand von Versuchsergebnissen verifiziert. Lateral torsional buckling of I‐sections with and without haunches — Design aids for a simplified check (part 1). In the highly stressed corners of frame structures often haunches are realized. Currently, the structural advantages of haunched members can be utilised efficiently for only a few special cases because of the lack of necessary information for the member checks. Design aids are presented that allow to perform the lateral torsional buckling check of members with and without haunches subject to bending by a hand calculation. These include aids for the determination of the ideal critical buckling moment and recommendations regarding the choice of an appropriate buckling curve. Finally, the presented design aids are verified by experimental results.