Keywords: steel structures, stability, ultimate strength, cold formed sections, local buckling, distortional buckling.

In this paper a nonlinear finite element model has been developed to make an in-depth investigation of the flexural behavior of simple beams composed of lipped channel cold formed sections subjected to uniform as well as non-uniform bending moments along the beam length. A group of sections varied in their dimensions (web, flange, lip,) are selected. In addition, a wide range beam slenderness is examined to draw a complete ultimate strength curve and explore the transition between the different modes of failure (local, distortional, and global). Both large deflection analysis and elasto-plastic material response have been incorporated in the model. The results of the numerical analysis indicated that, the lip depth to flange width ratio has a significant effect on the flexural strength of the beams when their failure shapes are associated with the distortional mode. Since, decreasing this ratio leads to a remarkable drop in the flexural strength of the beams. Moreover, the design strengths predicted using AISI-2007, and the direct strength method, DSM, are in good agreement with that obtained using finite element analysis, except for beams of intermediate overall member slenderness and short lip depth to the flange width, where the finite element results are slightly lower than that calculated using the design codes for this member slenderness range.

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