Minimum Stiffness Ratio of a Stiffener against Ultimate Strength of a Plate (2nd report)

Abstract

In the previous report, the authors clarified the existence of the minimum stiffness ratio, γUmin, of a stiffener against the ultimate strength of a stiffened plate in similar to the buckling strength, γBmin. In this report, elastic large deflection analysis is performed on the stiffened plate, and the phenomenon of the secondary buckling after the primary buckling is indicated. Then, a series of experiment is conducted to confirm the phenomena predicted by the theory.From these theoretical and experimental results, an approximate analytical method to determine γUmin is newly proposed as the intersection of the secondary buckling strength curve and ultimate strength curve of a locally failured plate, when there exists no initial deflection. When there exists initial deflection, the effective minimum stiffness ratio effγUmin is defined as the intersection of a curve of the initial yielding of bending stress of a stiffener and that of membrane stress of a plate. This method can also be applied to determine γUmin of a stiffened plate with arbitary aspect ratio and arbitary number of stiffeners.The effect of welding residual stresses on the buckling and ultimate strength is also discussed, together with on γUmin and effγUmin and the minimum stiffness ratio against the buckling strength, γBmin.