Behaviour of bi-axially loaded thin-walled tapered beam-columns with doubly symmetric sections

The behaviour of thin-walled tapered I-section members is governed by the width–thickness ratio of the plate elements along with the member slenderness and tapering ratios. The effect of this interaction has been studied theoretically in this work. A non-linear finite element model that allows for geometric non-linearities is constructed for the study. Large numbers of members having different values of flange and web width–thickness ratios along with different member lengths and tapering ratios were selected to draw complete ultimate strength–slenderness ratio curves and to study the different modes of failure. A series of interaction curves were drawn for design purpose with different normal forces and moments. An imperial equation fitting these curves was also presented. These curves alleviate the current complexity in the calculation of the effective width, providing a more flexible design procedure.