Compressive stress-strain model of cold-formed circular hollow section stub columns considering local buckling

A complete stress-strain model for cold-formed circular hollow section (CHS) stub columns under compression is proposed with emphasis placed on the modeling of post-local-buckling behavior. The proposed model comprises two mathematical expressions. One of the two equations is to define the ascending portion of the proposed stress-strain curve and depict the nonlinearity caused by residual stress induced during manufacturing process of cold-formed CHS, while the other is to define the descending portion and trace the post-local-buckling behavior. The proposed stress-strain model is a single parameter model. Only if the generalized outer diameter-to-thickness ratio is given, the compressive stress-strain relationship of a CHS can be completely determined. To calibrate the proposed model and verify its accuracy, test results of forty-eight CHS stub columns under compression are collected. The previous tests cover a wide range of structural factors such as outer diameter-to-thickness ratio and yield strength, particularly including CHS stub columns with yield strength of up to 1180 MPa. Comparisons between the measured results and the calculated ones indicate that the proposed model can not only predict the local buckling strength as well as corresponding strain, but also trace the post-local-buckling behavior up to large strain with high accuracy.