Study Of Ultimate Strength Of Hull Girder Considering Welding-induced Imperfection

The longitudinal ultimate bending capacity of a hull girder is very important in ship structure strength, and is to some extent influenced by the initial imperfection such as welding-induced residual stress, welding distortion and cracks. There are obvious discrepancy in the evaluation of ultimate strength using different idealizations and assumptions of initial imperfections. So it is very important to evaluate the welding imperfection accurately with appropriate method.In this article, the welding imperfection of stiffened plates are simulated through a thermal elastic-plastic finite element method and the ultimate strengths of the stiffened plates and hull with idealized section are studied. The work of this dissertation focuses on the following aspects:(1)The welding simulation of longitudinals in deck grillage is carried out through thermal elastic-plastic analysis based on shell/solid model. The welding behavior of the longitudinals is different with the stiffened plate with free boundary owing to the influence of boundary condition. In order to obtain reasonable results of welding induced-residual stress and distortion, proper boundary condition ought to be deal with when performing welding simulation of independent stiffened plate.(2)The welding simulation of the stiffened plate in a hull with idealized section is conducted with the simplified boundary condition considering the contribution of adjacent structure of the stiffened plate, to calculate the welding induced residual stress and distortion.(3)The ultimate strength of a hull with idealized section is studied based on the results of welding simulation of stiffened plates. The hull is dispersed into several stiffened plate elements and hard corner elements. The ultimate strength and post-buckling behavior of the stiffened plate is calculated by nonlinear finite element analysis considering the welding-induced imperfection. A progressive collapse analysis of the hull is then conducted based on the load-shortening curve of the stiffened plate by the nonlinear numerical analysis.