Keywords: cold formed steel platforms, embossments, imperfections.

The paper studies the buckling behaviour of cold formed steel beams in bending by applying nonlinear finite element analysis. These types of beams are usually used as platforms for scaffold configurations and exhibit some particular features such as the special embossments developed in the upper plate of the beam and the edge and intermediate stiffeners located in the compressive flanges. The cross-section of the cold formed steel platform is manufactured from a continuous steel sheet which is folded. The points at which the folded areas come in contact are connected by clinching.

Cold formed steel platforms are subjected mainly to bending, thus the possible failure mode is the local buckling that occurs in the most critical cross-sections. The aim of the paper is the estimation of the total carrying capacity of cold formed steel platforms and the comprehension of their failure mode.

For this reason a finite element model of 46,440 shell elements has been built, equipped with the appropriate boundary conditions, and a series of geometric analyses were conducted. The finite element model was able to take into account all the nonlinearities which are present in the physical problem such as the geometric and material nonlinearities and the contact phenomena as well. Two series of analyses were performed concerned with the perfect and imperfect structure. The possible contribution of the depth of the embossments and the quality of the connection of the interconnected plates at the ultimate load of the steel platform were examined in each case.

The results obtained from the various geometric nonlinear analyses shows that the steel platform fails due to a local instability phenomenon with an antisymmetric pattern in the loading region. The results of the nonlinear numerical analyses carried out for this paper, verify that the most important factor that affects the ultimate load of the platforms is the clinching distances in the longitudinal axis between the folded parts that shape the cross section.

The embossed area plays a rather insignificant role in the undertaking of the external loading so the total strength of the steel platform is affected in a minor way from the depth of embossments. This result is more pronounced for systems without initial imperfections. When initial imperfections are considered, it was found that the depth of the embossments affects the eigenmodes arising and finally affects, even in a minor way, the computed ultimate loads.

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