Nonlinear finite element bending analysis of Cold-Formed Steel of 'Z' section beams

Cold-formed steel Z section beams are widely used as the secondary structural members in buildings to support roof and sheeting or side cladding. In general, cold-formed steel sections are slender elements and have open and/or asymmetric cross-sections, where centroid and shear centre do not coincide. Therefore, during bending the section twists and deflects in both lateral and transverse direction resulting in the reduction of stiffness. Currently, design codes for this section use classical bending theory, which assumes load-deflection relationship to be linear and does not consider the effect of bending-torsion in the calculation of deflection. In CFS members for serviceability and deformation consideration, it is essential to consider the loss of stiffness due to the use of thin elements. Hence, this paper presents numerical investigations using the finite element method to check the accuracy of the linear analysis. A geometrical nonlinear analysis using ANSYS is performed on Z-beams with different section size and thickness to study the sectional deformation on its performance under bending. The obtained deformation verified the effect of bending-torsion in CFS cross-section. The predicted deformation characteristic curves at mid-span are examined and compared with linear solutions and maximum deflection predicted by serviceability limit states. The comparison showed that there is a significant difference in displacement between FEA nonlinear solutions and linear solutions, as well as serviceability deflection