Analytical and numerical calculation of the buckling stress for panels with closed‐section stiffeners

The forthcoming second generation of EN 1993‐1‐5 is bringing changes in terms of buckling and interpolation curves that allow the positive effects of torsional stiffness of closed‐section stiffeners to be taken into account. Regarding the determination of the critical buckling stress for global plate buckling, analytical or numerical methods may be used. FprEN 1993‐1‐5 provides a simplified analytical equation for determining the critical buckling stress of an equivalent orthotropic plate, which can also be found in the informative Annex A of EN 1993‐1‐5. The given equation does not take into account the torsional stiffness of longitudinal stiffeners with closed cross‐sections. The latter are often used in plated structures due to fabrication and strength benefits. This paper compares two methods for determining the elastic critical plate buckling stress that consider the positive effect of the torsional stiffness of closed‐section stiffeners. First, a newly proposed analytical method that accounts for the torsional stiffness of closed‐section stiffeners is derived on the same basis as the current equation in Annex A. Secondly, a numerical linear buckling analysis is performed on a large number of stiffened panels. The advantages and disadvantages of both methods are pointed out. Finally, both values are used to determine the ultimate resistance of plates and with GMNIA results from previous studies.