Recent research has characterized the behavior of panel beams with laterally unsupported compression flanges as either a complex local buckling mode or an overall buckling mode. Tests have shown that the behavior of the unsupported flange and web is similar to that of lateral buckling, except, rotation is enforced along the axis of the web and the tension flange--a behavior which may be described as distortional buckling. In the work described here, an analytical expression is presented for computing the elastic distortional buckling stress based on a model which treats the web and compression flange as an elastically restrained beam. The formulation is similar to those for lateral and torsional buckling. The effect of web local buckling on the rotational restraint of the outstanding leg is modeled explicitly using the effective width equations described in the AISI Cold-Formed Steel Design Manual. The analytical results from the distortional buckling expression are shown to agree reasonably well with numerical results generated from an elastic fInite strip buckling program (BFINST6). A design approach is suggested for estimating the ultimate moment capacity of a section subjected to the interaction between local and distortional buckling
