Ultimate capacity of I-slender section columns

The design provisions in most codes of practice usually use the concept of effective width to account for the presence of local buckling when calculating the ultimate capacity of slender sections. The expressions used to calculate this effective width are function of many variables. One of these variables is the state of stress within the section. This state of stress is usually calculated from the ultimate strength curves of compact sections based on the member slenderness ratio only. In this paper a non-linear finite element model is made to investigate the variation of this state of stress along with flange and web width-thickness ratios of slender I-sections for different member slenderness ratios. A group of slender I-sections that varied in their flange and web width-thickness ratios are chosen. A wide range of column slenderness ratios is selected to draw complete ultimate strength curves. Results show that the ultimate stress greatly depends on the interaction between the flange and web width-thickness ratios as well as on the member slenderness ratio. The ultimate strength curves are different from those of compact sections especially for members with low and intermediate member slenderness ratios. A proposed strength equation, which is function of the flange and web width-thickness ratios besides member slenderness ratio, is given. Finally, results are compared with the different design specifications. (C) 2003 Elsevier Ltd. All rights reserved.