Local buckling in cold-formed steel built-up I-section columns: Experiments, numerical validations and design considerations

Abstract

A series of axial compression tests were conducted on cold-formed steel built-up I-section columns consisting of two identical lipped channel sections connected by self-drilling screws at the web. At first, the buckling behavior, failure mode, and ultimate bearing capacity of columns with lipped channels and built-up sections were investigated. A nonlinear finite element model that can predict the built-up I-section column was established, and the model’s accuracy was validated against experimental results. Then, a method for estimating local buckling bearing capacity for built-up I-section columns under axial compression was proposed based on the local buckling critical stress calculation formula (Eq. (3)) in this paper, as well as the local buckling bearing capacity curve (Eq. (2)) of the current direct strength method. In order to simplify the calculation, based on revealing the mechanism of instability, two sets of simplified calculation formulas for local buckling critical stress suitable for different ranges of geometric parameters were given, namely Eqs. (23) and (24). Finally, the predicted capacity obtained using the proposed bearing capacity estimation method was compared with the experimental and supplementary finite element results. The comparison results show that the predicted bearing capacity of the built-up I-section column affected by the pure local buckling mode is in good agreement with the experimental or finite element results. However, this method leads to unsafe design predictions for columns with local-distortional interaction buckling.