Distortional Buckling of Thin-Walled Beams/Panels. I: Theory

Abstract

The introduction of the standing seam panel for roof systems provided the building industry with an efficient solution to watertightness problems. These panels have two major advantages over the conventional trapezoidal through-fastened panel: an elevated seam and concealed “hold-down” clips. The relatively small depth-to-width ratio of the panel guarantees that overall, the panel is laterally stable under gravity load. The capacity of laterally stable standing-seam panels may, however, be reduced due to lateral instability of the unsupported compression flange. This mode of instability has been referred to in the literature as distortional buckling—a form of instability for unsupported lengths between those for local and lateral buckling. In the present paper, an analytical expression, based on a beam on elastic foundation model, is presented for estimating the elastic distortional buckling stress in sections with laterally unsupported compression flanges. The beam is assumed to comprise the outstanding leg, and the elastic foundation is provided by the rotational restraint of the tension flange and the web. A comparison of the analytical results with the results from elastic finite-strip buckling analyses shows good agreement between the two methods of analysis.