Development of simplified model for buckling collapse analysis of plates and stiffened plates under cyclic loa

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A simplified model to calculate the buckling/plastic collapse behavior of plates and stiffened plates under in-plane cyclic loads was developed. First, it was proved by the material test that the two-surface nonlinear strain-hardening model proposed by Dafalias and Popov could accurately simulate the stress-strain relationship of mild steels under cyclic loads. The cyclic buckling test of both-end simply supported angle-bar columns was performed, and the results were compared with the results of Finite Element Analysis (FEA) using the two-surface model. Good agreements were obtained. It was also found that the initiation of crack at the locally buckled region is more likely to take place at the compression-side of bending than the tension sides, as a result of larger strain range due to the action of in-plane load and the deterioration of material toughness due to the pre-compressive strain after initial buckling. The FEA was further performed for a simply supported rectangular plate typical in ship structures, subjected to uni-axial cyclic in-plane load. It was recognized that the accumulation of tensile membrane strain at the unloaded edges could become a trigger to the crack initiation. Finally, a new simplified model for collapse analysis of plates and stiffened plates was developed within in the framework of the Idealized Structural Unit Method (ISUM). By idealizing material and geometrical nonlinearities, larger structural units are defined as an element in ISUM than in conventional FEA.This mode can easily cope with any type of strain-hardening model including the two-surface model. Comparisons with FEA demonstrated the high applicability of the proposed model to typical plates in ship structures subjected to in-plane cyclic loads.