Development of an OpenSees model for collapse risk assessment of Italian code-conforming steel single-storey buildings

This paper aims at evaluating the risk of collapse in single-storey steel buildings designed according to the current Italian Seismic Design Code. A set of case studies made by buildings having different geometries and located in sites having different seismic hazard is modelled and subsequently analysed within the OpenSees software framework. An accurate structural model is developed and an insight into the main modelling aspects is given, in order to share with the OpenSees community the main modelling strategies adopted. The model developed here accounts for both mechanical and geometrical nonlinearities: the former by adopting a distributed plasticity model for beams, columns, and concentric braces; the latter by using a corotational coordinates transformation for all the elements. The out-of-plane buckling phenomenon on compressed lateral bracing systems is simulated by assigning proper local imperfections (i.e., initial curvature) to the braces and including the gusset plates deformability and relevant post-elastic behaviour. Since the seismic design follows capacity design principles, hysteretic behaviour of the joints is not considered as joints are no-dissipative elements. In addition, due to the geometry of beams, columns and braces, yielding in shear is excluded and a linear elastic behaviour in shear is used in the model. Push-Over analyses are used for a preliminary evaluation of the nonlinear behaviour under increasing horizontal loads. Afterwards, multi-record incremental dynamic analyses are performed for 10 increasing seismic intensities.