On the buckling of longitudinally stiffened plates, part 2: Eurocode-based design for plate-like behaviour of plates with closed-section stiffeners

Buckling resistance of longitudinally stiffened orthotropic plates is highly important in the design of steel bridges. The current calculation method of Part 1.5 of Eurocode 3 is based on the concept that the behaviour can be superposed from plate-like and column-like behaviours. Recent results indicate uncertainties in the application of the current method, e.g., if applied to plates with closed stiffeners. It is also known that the critical buckling stress is dependent on how it is calculated: by using a shell finite element model or by using the equations from Annex A of the relevant code part. The two calculation methods can lead to significant differences in the critical stress, which then mirrored in the resistance. Some results indicate that shell finite element calculation of the critical stresses can lead to resistance overestimation, especially when closed stiffeners are used. However, the reasons of the differences between the numerically and analytically calculated critical stresses are not yet fully clarified. Therefore, in the current paper the elastic critical buckling stress and buckling resistance of longitudinally stiffened plates are discussed. The paper presents the results of an extensive numerical research program focusing first on the critical buckling stress, then on the buckling resistance of plates with closed stiffeners. Reasons of the experienced differences between the critical stresses are explained in full detail. Moreover, possible enhancement of the resistance prediction is indicated.