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Développement d’un modèle de stabilité des barres à section tubulaire comprimées fléchies sensibles aux effets du second ordre

Abstract : This thesis is part of an effort to improve knowledge of the instabilities of beam-columns sensitive to second-order effects. The works deal with the means to take into account the initial imperfections in the structural analysis and to adapt the current verification criteria for tubular section structures, such as scaffold structures. The existing formulations, proposed in the litterature and calculation codes, are often based on hypotheses, and thus lead to inconsistencies between, on the one hand, the verification criteria in section, and on the other hand, the verification criteria in instability. The developed approach takes into account the interaction between section resistance and instability phenomena, and includes the influence of initial imperfections (initial defect of aplomb, lack of straightness, residual stresses). As far as possible, these effects will be decoupled. As such, a method has been developed to allow the definition of initial imperfections of a structure, to be as accurate as possible. This method, based on the definition of a single imperfection, identical in appearance to the shape of the predominant critical buckling mode, is a precise, fully defined method to take into account the geometric characteristics, intrinsic mechanical characteristics, limits and the form of loading, in the definition of the initial imperfections of a structure. A test campaign was carried out in collaboration with the French Syndicate of Scaffolding, Formwork and Shoring (SFECE), aiming to analyze the experimental behavior of buckling of cold-formed tubular sections. Nine buckling tests on scaffold ladders, from various European suppliers, have been carried out. A statistical study of the experimental results has made it possible to highlight that the imperfection factor currently defined for the cold-formed tubular sections is far too penalizing for the sections used in the field of scaffolds. In order to respond to the problem, new instability criteria have also been established using a similar approach to that of Ayrton-Perry. These new criteria make it possible to free ourselves from the modeling of initial imperfections while offering a safe and accurate estimate of the stress factor of a structure. A comparative study was conducted in order to ensure the safety of the proposed formulations as regards the section verification criteria of the NF EN 1993-1-1 current standard.
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Submitted on : Thursday, January 30, 2020 - 10:53:41 AM
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C. Mercier. Développement d’un modèle de stabilité des barres à section tubulaire comprimées fléchies sensibles aux effets du second ordre. Structures. Université de Lorraine, 2019. Français. ⟨NNT : 2019LORR0113⟩. ⟨tel-02457004⟩



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