Structural performance of cold-formed steel elliptical hollow section pin-ended columns

The structural performance of cold-formed steel elliptical hollow section pin-ended columns buckled about the minor axis was studied through experimental and numerical investigation. Four cross-section series with five different column lengths were designed in the test program to include a wide range of cross-section geometries and column slenderness. Finite element model was developed to replicate the key test results and to perform extensive parametric study. The validation results show that the model can accurately predict the behavior of cold-formed steel elliptical hollow section pin-ended columns buckled about the minor axis. Subsequently, an extensive parametric study with a wide range of cross-section geometries and a spectrum of column slenderness was performed. Since currently there is no codified design rule on elliptical hollow section compression members, the results of 22 column tests and 280 finite element analyses were only compared with the predicted strengths by the equivalent diameter method and equivalent rectangular hollow section approach proposed by previous researchers, the traditional design methods with equivalent diameter incorporated as well as the Direct Strength Method. Reliability analysis was conducted to examine these design methods. Among these design methods, the comparisons show that the existing Direct Strength Method offers the most suitable design provisions, though further improvement remains possible. In this study, modification is proposed on the Direct Strength Method to further improve the accuracy of design strength predictions. It is suggested to adopt the modified Direct Strength Method design equations in the nominal strength predictions of cold-formed steel elliptical hollow section pin-ended columns buckled about the minor axis.