Buckling Analysis Design of Steel Frames (No. R891)

Abstract

Steel design codes do not provide sufficient information for the efficient design of steel structures against out-of-plane failure, and what is provided is often overly conservative. The method of design by buckling analysis corrects this situation for beams, but the extension of this method to columns is only suggested, while there is no guidance on how to apply this method to the design of beam-columns and frames. Beam design by buckling analysis uses the design code formulation for the member nominal design strengths in terms of the section moment capacities and the maximum moments at elastic buckling, accurate predictions of which may be determined by available computer programs. Column design by buckling analysis is similar to beam design, in that it uses the design code formulation for the column nominal design strengths in terms of the section compression capacities and accurate predictions of the elastic buckling loads which may also be obtained from computer programs. However, design codes do not provide formulations for the direct buckling design of beam-columns, but instead use the separate results of beam design and column design in interaction equations. The further extension to frames is not directly possible, because frames are not designed as a whole (except through the rarely used methods of advanced analysis), but as a series of individual members. This paper shows how the method of design by buckling analysis can be used to design beam-columns and frames as well as beams and columns. Two example frames are designed and very significant economies are demonstrated when the method of design by buckling analysis is used.