A simple diagonal stiffener is proposed as a solution to premature local flange and web buckling of plastically designed members in pitched-roof portals and continuous beams. This solution is developed from theoretical predictions and experimental results, which also show that existing Codes do not allow for certain effects which significantly reduce the rotation capacity of members under moment gradient, particularly the influences of span and coincident axial force. A new model is proposed
for the interaction between local flange, local web, and lateral-torsional buckling of plastically designed members, which compares favourably with earlier test results. The stiffener arrangement approximately doubled the rotation capacity in five pairs of stiffened and unstiffened test specimens in which the critical modes were local flange or web buckling.
Professor A.R. Kemp