Structural response of cold-formed lipped Z purlins-Part 2 numerical modelling and optimisation of lip size

This paper reports a numerical study on the optimisation of the lip size of Z-sections under gravity loads. Numerical models of cold-formed steel Z purlins restrained by cladding and angle struts and subjected to sagging moment were developed and validated against a total of 8 experimental results on Z-sections that failed in local or/and distortional buckling reported in the companion paper. Models of varying levels of complexity were generated and the key parameters affecting the structural response were determined by means of a sensitivity analysis. The investigated parameters included the magnitude, shape and combination of initial geometric imperfections pertinent to local and distortional buckling and the simplified or explicit modelling of test details such as struts and sheeting. Having determined the appropriate modelling strategy that leads to the best balance between accuracy and computational cost, parametric studies were conducted to investigate the effect of decreasing or increasing the lip depth on the sections? moment resistance and corresponding failure mode. Based on the parametric study results, the optimal lip size which maximizes the moment to weight ratio for each section was determined. Finally, all generated FE results are utilized to evaluate the accuracy of the moment resistance prediction of EN 1993-1-3 and the Direct Strength Method.