Convergence Study On Asymmetrically Flexural Problem of Cold-formed Channel Sections

Current Direct Strength Method equations computing flexural strength of cold-form members were reported to be over-conservative when applied to members bent about the asymmetrical axis. Finite Element Analysis was used to develop new equations. However, the convergence study, which ensures the accuracy of the Finite Element Analysis result, has not been presented clearly. Thus, this paper performed a convergence study on the strength problem of channel-section asymmetrically flexural members having the web in compression. 33 cold-form channel cross-sections utilized in Oey and Papagelis’ study were modeled into ABAQUS to calculate the elastic buckling moment and the ultimate strength. Two factors affected the accuracy of the models, i.e., the mesh size, being 5 mm, D/20, D/40, and D/60, and the member length, ranging from 0.3D to 7D, where D is the cross-section height, were examined. The investigation shows that the seeding method considering the local buckling of the web is the most justifiable. Therefore, the seed size being 1/40 the cross-section height is suggested. This seed size is proven to produce results with reasonable accuracy.  To avoid the end effect as well as the influence of incorrect half-wavelength, it is recommended that the member length should be chosen as greater than or equal to two times the cross-section height, and the lengthier the better.