Dieser Aufsatz befasst sich mit dem Beulnachweis nach DIN EN 1993‐1‐5 Abschnitt 10. Es wird detailliert das Vorgehen und die Nachweisführung erläutert. Hierbei wird ein Flussdiagramm zur Anwendung der Methode der reduzierten Spannungen vorgestellt. Anschließend werden offene Fragen zum Beulnachweis aufgelistet und hierzu Empfehlungen und Klarstellungen gegeben. Für ein Beulfeld unter mehraxialer Beanspruchung wird ein Beispiel vorgestellt, um die Nachweisführung und die Anwendung der Empfehlungen aufzuzeigen.

The buckling behaviour of panels may be determined according to EN 1993-1-5 [1]. Most of the design rules relating to stiffened panels in EN 1993-1-5 were derived on the basis of opensection stiffeners. Several recent investigations have shown that the application of the design rules according to EN 1993-1-5 considering the torsional stiffness of the stiffeners may overestimate the resistance of the panels. Therefore, the recent Amendment A2 to EN 1993-1-5 states that the torsional stiffness of stiffeners should generally be neglected in determining critical plate buckling stresses. In addition, prEN 1993-1-5 [2] provides rules for considering the torsional stiffness of stiffeners. However, in this article it is shown that even the rules of prEN 1993-1-5 are not sufficient to overcome the safety deficiencies. The article focuses on the investigation of the buckling behaviour of stiffened panels with closed-section stiffeners subjected to constant longitudinal compression stresses. Improved rules have been developed that allow to consider the torsional stiffness of the stiffeners. Based on an extensive numeri cal parametric study, a new interpolation equation be tween column-and plate-like behaviour is proposed. In comparison to [3], the investigations have been extended to the effec tive width method. They show that the proposal provides a safe and economic solution for the reduced stress method and the effective width method when considering the torsional stiffness of stiffeners by calculating the critical plate buckling stresses.Keywords bridge design; plate-like behaviour; column-like behaviour; stiffened panel; longitudinal; reduced stress method; effective width method; torsional stiffness of stiffenerThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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Stichworte Beulnachweis; Methode der reduzierten Spannungen; Torsionssteifigkeit; Längssteifen; mehrachsige Druckbeanspruchung; Stahlund Stahlverbundbrücken; Taktschiebeverfahren;DIN EN 1993-1-5 on the influence of the torsional stiffness of longitudinal stiffeners with panels under biaxial compression stresses During the incremental launching of steel and composite bridges, the superstructure's slender web plates are temporarily exposed to multiaxial compressive stresses. Along with longitudinal stresses due to the bending moment, there are transversal compressive stresses acting on the web at the launch bearings. Often, this construction stage is governing for the structure's design. In Germany, an analytical design approach for longitudinally stiffened webs requires the application of the reduced stress method of DIN EN 1993-1-5. Current investigations showed that if longitudinally stiffened plates with closed section stiffeners are exposed to uniaxial compression and the critical buckling stresses are calculated under consideration of the torsional stiffness of the longitudinal stiffeners, the method may lead to unsafe design results. Since November 2018, the rule to neglect the torsional stiffness in these cases has been introduced into the German National Annex to DIN EN 1993-1-5 and since October 2019 it is also part of DIN EN 1993-1-5. In a recent master thesis the effects of closed-section stiffeners with a high torsional stiffness on the structure's failure load and mode under multiaxial compression have been investigated. This was done by a numerical parametric study, where the findings have been compared to the design results of the reduced stress method of DIN EN 1993-1-5. Recommendations on design approaches have been developed.

The buckling behaviour of panels may be determined according to EN 1993‐1‐5 [1]. Most of the design rules relating to stiffened panels in EN 1993‐1‐5 were derived on the basis of open‐section stiffeners. Several recent investigations have shown that the application of the design rules according to EN 1993‐1‐5 [1] taking into account the torsional stiffness of the stiffeners may overestimate the resistance of the panels. Therefore, the recent Amendment A2 to EN 1993‐1‐5 states that the torsional stiffness of stiffeners should generally be neglected in determining critical plate buckling stresses. In addition, prEN 1993‐1‐5 [2] provides rules for considering the torsional stiffness of stiffeners. However, in this paper it will be shown that even the rules of prEN 1993‐1‐5 are not reliable as far as torsional stiffness is concerned. The paper focuses on the investigation of the buckling behaviour of stiffened panels with closed section stiffeners subjected to constant longitudinal compression stresses and shows improved rules to consider the torsional stiffness of the stiffeners. For this purpose, a new interpolation equation between column‐like and plate‐like behaviour is proposed, based on an extensive numerical parametric study. The proposal provides a safe and economic solution, as it considers the torsional stiffness of stiffeners when applying the rules of prEN1993‐1‐5.