An accurate wrinkled membrane model for analysing the post-critical behaviour of stiffened plate-girders

Summary. In this paper a model is presented to analyse the post-critical behaviour of elastic plate girders with very thin web subject to in-plane loads. Flanges and stiffeners are modelled as beams while the web is treated as an ideal membrane unable to sustain compressive stresses. To derive the tension field within web panels the linear wrinkled membrane theory is used where a relaxed strain energy density is assumed for the web. The model permits an accurate determination of the interactions between flanges, stiffeners, and adjacent panels, so the role carried out by each component is clearly highlighted. Two example cases of built-up metallic I-beams with different web stiffening are considered as an application. The effects of the most influential parameters on the post-critical response of the girder are investigated showing at the same time how currently used design rules tend to overestimate the real load-bearing capacity.