Some experiences on numerical modelling of cold-formed steel lapped Z-sections

Cold-formed steel purlins are widely adopted in building construction as supporting members of roof systems. Owing to the effective overlapping between Z-sections, they are commonly adopted to act as multi-span purlins and side rails to support building envelopes. This paper presents a systematic numerical investigation into the structural behaviour of high strength cold-formed steel lapped Z-sections under one point loads. A number of finite element models with two different element types and mesh configurations have been established with different boundary and contact conditions, and material and geometrical non-linearity has been incorporated into the finite element models together with initial geometrical imperfections. The models are calibrated against the test results of a series of lapped Zsections with different lap lengths. It is found that the maximum applied moments and the elastic deformation characteristics predicted by the models with both thin degenerated 4- noded shell elements and continuum 8-noded shell elements are very close to the measured results. However, only the numerical models using continuum 8-noded shell elements are able to give close predictions to the deformation characteristics of continuous Z-sections at very large deformations. Hence, with suitable boundary and contact conditions, the finite element models using continuum 8-nodoed shell elements are shown to be highly effective in assessing the structural behaviour of lapped Z-sections with different lap lengths along their entire deformation ranges.