Cold-formed steel beam-to-column bolted connections for seismic applications

Cold-formed steel (CFS) portal frames are gaining increased popularity around the world. The structural performance of these frames is to a large extent controlled by the CFS beam-to-column connections, which in most practical applications transfer the loads through the beam web using a gusset plate, while the flanges are left unconnected. This can lead to premature local buckling failure of either the CFS beam web in the connection zone or the gusset plate, leading to poor seismic performance. This paper aims to develop two new connection configurations which engage the flanges in the connection behaviour. In conjunction, practical seismic design recommendations are presented, which allow a balance between the load carrying capacity of the connections and their seismic performance to be reached. Detailed Finite Element connection models, taking into account material nonlinearity and initial geometric imperfections, are developed and validated against experimental data. The validated FE models are then used to conduct a comprehensive parametric study to investigate the effects of key design parameters, including the beam thickness and the gusset plate shape and thickness, on the moment–rotation behaviour of the connections. Based on the results, suitable connections, which balance strength with seismic performance, are introduced. Their seismic performance is evaluated in terms of ductility, energy dissipation and damping coefficient, leading to some practical design recommendations commensurate with different seismic performance levels.