Buckling/Plastic Collapse Behaviour And Strength of Bilge Circle And Its Contribution to Ultimate Longitudinal Strength of Ship¿s Hull Girder Available to Purchase

The most fundamental aspect of the strength of a ship structure is that of longitudinal strength, that is, the ability to withstand longitudinal bending under operational and extreme loads without suffering failure. To evaluate the longitudinal ultimate strength of a ship's hull girder applying a simplified method, its bilge circle is usually considered as a hard corner which does not undergo buckling collapse. However, it should be noticed that the bilge circle may undergo local buckling. In the present paper, to clarify the buckling behavior of the bilge circle part and to estimate its influence on the ultimate longitudinal strength of a ship's hull girder, a fundamental study was performed. At first, a series of elasto-plastic large deflection analysis was performed on the bilge circle part of a ship's hull girder applying the FEM changing the radius to thickness ratio, R/t, and the radius to length ratio, R/L, of the bilge circle as well as the yield stress of the material, and its buckling behaviour was clarified. It was found that fundamentally plastic buckling takes place after a fully plastic condition is satisfied all around the bilge circle area and then the capacity decreases. On the basis of the calculated results, simple formulas were derived to represent the average stress-average strain relationship of the bilge circle part under axial compression including the influences of buckling and yielding. In the formulas, the ultimate strength was expressed in terms of the yield stress and R/t ratio, and the plastic buckling strain in terms of R/t ratio. Average stress-average strain beyond the buckling point was represented by modifying the results of rigid plastic mechanism analysis on a plate in compression. Then, this relationship was implemented into the existing code for progressive collapse analysis of a ship's hull girder subjected to longitudinal bending.