Nonlinear instability analysis of long-span roofing structures: The case-study of Porta Susa railway-station

Instability problems are going to be more and more important for long-span structures, especially for those where structural shape and loading capacity are strictly correlated. In view of this, a complete buckling analysis seems to be essential for the correct prediction of structural behaviour. At the same time, recent disasters, occurred in the last few years, such as the collapse of the new pavilion of Charles de Gaulle Airport in Paris (2006), have brought the instability of shallow long-span roofs at the cutting edge of structural engineering research. In this paper, different studies devoted to the stability of the large span roof of the new railway station of Porta Susa in Torino (Italy) are proposed. In particular, 2D models were realized in order to evaluate in-plane linear and nonlinear instabilities for different loading and restraining conditions of the steel arches constituting the bearing framework of the roof. These arches have been subdivided into different groups according to the geometric characteristics. It has been found that nonlinear analyses are able to give not only an interpretation of the post-buckling behaviour, but also a more correct evaluation of the safety factor for this kind of structures. Moreover, a parametric evaluation, taking into account different cross sections, is presented. The results reveal that much slender arches would offer the same safety factor as the existing ones due to the activation of a different resisting mechanism, although with an evident reduction in the employed material. Finally, the outcomes of this case-study could be generalized in order to investigate the behaviour of other structural typologies and to suggest alternative design approaches.