Distortional Buckling Curves for Composite Beams

Abstract

This paper presents simple elastic analysis of uniformly loaded composite steel‐concrete beams simply supported, but with an additional spring having arbitrary stiffness to restrain in‐plane rotation at each end that can become infinite, to give clamped ends. Thus it is possible to represent members continuous over internal supports. The analysis allows for the difference between sagging and hogging bending rigidities along the member, using a simple approach of comparing areas under the curvature diagram of the beam. Hence design curves are presented that model the buckling of the lower flange in its own plane. These can be used for any combination of clamped, simply supported and free in‐plane end conditions of the flange. This enables distortional buckling stresses and end bending moments, plus the uniformly distributed loads causing them, to be predicted for a very wide range of composite beams with reinforced slabs of any probable proportions. Therefore the curves can be considered to form a concise parametric study, covering a wide range of beam sections. Their use is illustrated by an example.