A RATIONAL MODEL FOR THE DISTORTIONAL BUCKLING OF TAPERED MEMBERS

A general finite element is developed for the analysis of coupled loca l and lateral buckling of steel structures composed of tapered I-secti ons. Structures such as gable frames and steel bridges fall into this category. The present method is capable of considering both the taperi ng of the flanges as well as the web. The effect of vertical web stiff eners is handled automatically, and loading remote from shear centre c an also be incorporated. The analysis is performed in two stages: in-p lane and out-of-plane. The resultant in-plane stresses are used for th e out-of-plane initial loading pattern. This arrangement results in a general eigenvalue problem, where the buckling load and mode are found using algorithms such as the Sturm Sequence and Random Force Vector m ethods. The accuracy of the method is then demonstrated in several exa mples incorporating tapering of both kinds. Finally, the method is use d to investigate the significance of distortion in the buckling of a t ypical gable frame under gravity loads.