FLEXURAL AND FLEXURAL-TORSIONAL BIFURCATION OF LOCALLY BUCKLED BEAM-COLUMNS

The paper describes the overall bifurcation behaviour of locally buckl ed I-sections in combined compression and major axis bending. The over all bifurcation loads are calculated using the tangent rigidities of t he locally buckled cross-section for minor axis flexure and warping to rsion. The expression for the overall bifurcation load is analytic whi le the tangent rigidities are calculated numerically using an elastic nonlinear finite strip local buckling analysis. It is shown that while the interaction curves for local buckling and overall flexural-torsio nal buckling of the undistorted cross-section are convex, the interact ion curves for the flexural torsional bifurcation of locally buckled b eam-columns may be convex, linear or concave depending on the cross-se ction geometry and the extent of local buckling. It is demonstrated th at the overall bifurcation load depends primarily on the local bucklin g of the flanges. The overall bifurcation load of sections that ave lo cally buckled in the web only is virtually unaffected by local bucklin g for any combination of bending and compression. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.