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Abstract Thin-walled cold-formed steel structural members occupy an important part in the field of modem structural engineering because of their low weight to strength ratio and their ease of fabrication. Because of large width to thickness ratio of the component plates of the cross-section, they are subjected to local buckling, overall buckling in addition to the common yield failure criterion. Current design of cold-formed steel members, especiaJ1y those having high slenderness ratio of cross section component elements, is basicall y dependable on using the effective area of cross section based on von Karman approach. This leads to a complexity of the design of cold-formed steel members. Therefore, the main purpose of the present research is to investigate (experimentally and theoretically), the influence of web depth-to-thickness ratio and web depth to flange width ratio on the ultimate capacity of cold-formed thin-walled beam-columns. An experimental program has been conducted on 15 box-section beam-column specimens loaded axially up to failure. A parametric study was conducted, using the finite element model, on a variety of thin walled box-sections representing columns, beams and beamcolumns. The section ultimate capacities were determined and plotted in the form of interaction curves. The results of the finite element model were used to develop design equations to predict the ultimate strength of thin-walled box-sections subjected to pure moment and or pure normal force. In the proposed approaches, designers need to compute only the proposed buckling factor (:I<.”ooel) which takes into account web-flange interaction and they have to use the total gross sectional area to find the ultimate strength of columns, beams and beam-columns of thin walled box-sections. |