Cyclic behaviour of bolted cold-formed steel moment connections: FE modelling including slip

In this paper a Finite Element (FE) procedure is described for simulating hysteretic moment–rotation behaviour and failure deformations of bolted cold-formed steel (CFS) moment connections. One of the main challenges in modelling the response of bolted connections is the presence of bolt slip. A series of six beam–column assemblies comprising CFS curved flange beams, a support column and a through plate were tested under cyclic loading. The moment–rotation behaviour of the connections was dominated either by flexure in the beams or by bolt slip in the connections. FE models presented in this paper incorporate geometrical imperfections of the beams, material properties obtained from tensile coupon tests and bolt slip to address these two types of behaviour. The updated FE models result in an accurate prediction of the hysteretic moment–rotation behaviour of the connections dominated by a flexural behaviour in the beams. A simplified cyclic slip model which allows slip at a specified reduced slip resistance load simulates reasonably well the hysteretic behaviour of connections dominated by bolt slip. Using the updated FE model, the failure modes of the connections predicted by the simulations also agree well with those observed in the experiments.