Strength of Elastically Stabilized Beams

The compression flange of a beam is treated as a column that, in this case, is laterally unsupported except through the elastic restraint from the web. The tension flange is assumed to be laterally supported and torsionally restrained by a diaphragm or stringers. Included are the effects of shape distortion of the tension flange and web. Equations are developed for the critical buckling stress of the compression flange as a function of the elastic properties of the stringers, diaphragm, and the beam itself. The compression flange is assumed to be any open shape. Various tension flanges are considered, including lipped types. The degree of error and advantages of Engesser's formula are investigated. The critical stress for A-36 rolled shapes generally is not reduced if a rigid joint at the tension flange is provided. Roll formed aluminum sections and thin web steel girders show stress reductions ranging from moderate to severe.