Research On The Ultimate Strength Of Hull Girder Under Cyclic Bending Moment

The longitudinal ultimate strength of hull girder is of great significance for ensuring the safety of the ship. The researches on this field have been made great progress in the past few decades and several kinds of practical method have formed which are all built on the basis of the static ultimate strength criteria, i.e. the overall destruction of hull girder is caused by the bending moment increasing to its limit in one time. However, the reality is, when the ship subject to periodic cyclic bending loads during the voyage, a certain degree of yield or buckling failure and plastic deformation maybe occur for some of the longitudinal component of the hull girder, leading to the decrease of the load carrying capability of the hull girder. This paper has studied the effect of cyclic bending moment on the ultimate strength of the hull girder and drew some meaningful conclusions. The following items are studied in this paper:1) The ultimate strength of a rectangular plate under in-plane loading as well as the stress-strain and the stress-deflection relationship during different phases of deformation is studied based on the elastic large deflection analysis and the rigid plastic analysis.2) The ultimate strength of the stiffened panel under in-plane loading based on different failure modes is studied. On this basis, the deformation performances of the stiffened panel during different stages of loading and unloading are discussed. The performance of the stiffened panel is studied using the beam-column theory and the decrease of the ultimate strength of stiffened panel is attributed to the increase of the initial eccentricity of beam-column during the cycles. The calculation method is programmed using the fortran90language and a typical stiffened panel of hull girder is computed. The assumption of the paper proved to be reasonable.3) The paper describes a methodology of computing the ultimate value of the longitudinal bending moment of the hull girder after a certain circulation process on the basis of the progressive collapse analysis which is programmed using the fortran90language. 4) Some characteristics of the ultimate strength of hull girder after certain circulation processes are discussed by take a box beam and a ship as examples.