Stiffened steel plates have been used for many years especially in the fields of bridges, ships and towers. They are very efficient components of a structure, having both a high strength - to -weight ratio and a pleasing appearance. However, in some cases they have a tendency to buckle in one mode or even two simultaneous modes. In existing codes of practice designers have been supplied with many comprehensive rules so that they can calculate failure loads (collapse conditions) and the loads at which first yield occurs (serviceability conditions). A key calculation in each of these...