Numerical analysis of semi-elliptical hollow section columns

The buckling behaviour, ultimate strength and failure of columns with semi-elliptical hollow section are examined in this paper, using finite-strip analyses and shell finite-element analyses. Semi-elliptical hollow sections are a unique case of section shape, since they possess a flat part (plate behaviour) and a semi-elliptical part (shell behaviour). Assessing the contribution of each part to the buckling and ultimate behaviour of semi-elliptical hollow section columns is the main objective of this paper. The buckling behaviour is first analysed using finite-strip software and the ultimate behaviour is then studied using shell finite-element software. From the finite-strip results it is shown that local buckling of semi-elliptical hollow section columns is solely governed by the instability of the flat part. From shell finite-element results it is shown that the ultimate behaviour is mostly governed by the pre-buckling stiffness of the semi-elliptical part. Some columns have ultimate loads well above the critical load (associated with local plate buckling) due to the stiffness of the semi-elliptical part, for which the buckling stress is much higher than that of flat part. Finally, some preliminary design guidance is proposed. An expression to predict the ultimate strength is presented and shown to provide accurate results.