Keywords: steel frames, second order effects, analysis methods, design criteria, amplification factor, sway buckling strength, portal frames, modelling, rotational springs, translational springs, structural engineering
A unified approach for assessment of second–order effects and sway buckling strength in steel portal frames
The objective of this paper is to propose a criterion for the importance of second–order effects, the choice of the appropriate analysis method and the buckling strength of steel portal frames. To that effect, a model of a column with rotational springs at the two end nodes as well as a translational spring at the top node is proposed. Using the above model analytical expressions for evaluation of the buckling strength of columns in multi–story sway, non–sway as well as partially–sway steel frames are derived. The importance of second–order effects is derived using the same model by proposing a set of graphs providing the ratio of second order moment to first order moment of the frame columns, depending on the boundary conditions. These graphs are used for the choice of a suitable analysis method. Comparisons to geometrically non–linear analysis results for several example frames are used for verification.