Longitudinally stiffened plates are commonly used to increase the resistance to plate buckling. Closed cross‐section stiffeners provide high values of the torsional stiffness and thus are very efficient to avoid their premature lateral torsional buckling. With the current software tools, it is easy to assess the critical stress for the elastic global mode, taking into account the beneficial effect of these high values of torsional stiffness for stiffeners with closed cross‐sections. However, the torsional stiffness of longitudinal stiffeners is not considered in the analytical formula proposed by Annex A of EN 1993‐1‐5 for the assessment of the global buckling critical stress. A study is presented here where the effect of the torsional stiffness of longitudinal stiffeners on the plate buckling criterion of EN 1993‐1‐5 has been analysed. 216 configurations of stiffened plates were calculated through finite element GMNIA non linear analyses. Their compressive strength thus obtained were compared to their resistance to plate buckling as predicted by EN 1993‐1‐5, either by considering their torsional stiffness with EBPlate software or by completely ignoring it. The study clearly shows that EN 1993‐1‐5 leads to unsafe results when the torsional stiffness is taken into account in the calculations. Finally, it is concluded that the torsional stiffness of longitudinal stiffeners has to be ignored in the design of stiffened plates according to EN 1993‐1‐5.

In bridge construction, the use of stiffened plates for box-girder or steel beams is common day to day practice. The advantages of the stiffening from the economical and mechanical points of view are unanimously recognized. For curved steel panels, however, applications are more recent and the literature on their mechanical behaviour including the influence of stiffeners is therefore limited. Their design with commercial finite element software is significantly time-consuming, which reduces the number of parameters which can be investigated in an optimization procedure. The present paper is thus dedicated to the study of the behaviour of stiffened curved panels under uniform longitudinal compression. It addresses the linear buckling and the ultimate strength which are both influenced by the coupled effects of curvature and stiffening. It finally proposes a design methodology based on that for stiffened flat plates adopted by European Standards and a column-like behaviour

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International audienceIn bridge construction, the use of stiffened plates for box-girder or steel beams is common day to day practice. The advantages of the stiffening from the economical and mechanical points of view are unanimously recognized. For curved steel panels, however, applications are more recent and the literature on their mechanical behaviour including the influence of stiffeners is therefore limited. Their design with actual finite element software is possible but significantly time-consuming and this reduces the number of parameters which can be investigated to optimise each panel. The present paper is thus dedicated to the development of a preliminary design formula for the determination of the ultimate strength of stiffened cylindrical steel panels. This approximate formula is developed with the help of a design of experiment method which has been adapted from the current statistical knowledge. This method is first presented, and its feasibility as well as its efficiency are illustrated through an application to the reference case of unstiffened curved panels. Then, the case of stiffened curved panels is investigated and a preliminary design formula is developed. The ease of use of this formula for preliminary design is finally illustrated in a cost optimisation problem