Failure mechanisms of TWCFS members considering various eccentricities

Thin-walled cold-formed steel elements represent an attractive structural solution due to the fast manufacturing and erection time on-site. Their small thickness leads to imperfection and sensitivities to eccentricities. An experimental programme was performed on short members with lipped channel cross section, subjected to eccentric compression about the minor and major axes, in a large range of eccentricities. The specimens were manufactured on a folding machine. Before testing, the dimensions of all specimens were measured. Shortening of all specimens was measured in two ways, i.e., 1) using the displacement gauge integrated with the machine crosshead beam and 2) from deformation fields obtained using digital image correlation (DIC) system. The quantitative results, presented as the ultimate loads versus the eccentricity curve, emphasise the influence of the eccentric load on the capacity of the element. Finite element (FE) analyses were performed to simulate the behaviour of short members in eccentric compression using the commercial FE software ABAQUS/CAE and ANSYS. Static non-linear analyses were conducted in displacement control. Both geometrical and material nonlinearities were included. An isotropic linearly elastic-perfectly plastic constitutive model was considered, with von Mises yielding the criterion and associated flow rule. Failure modes were identified due to numerical and experimental tests. Plastic mechanism models were derived, resulting in the derivation of post-ultimate, rigid-plastic curves, characterising a post-ultimate structural behaviour.