There are many deep girders in a ship structure as the main strength members. Under increasing loads, local failures, such as buckling, yielding etc., occur in these members. These phenomena decrease the stiffness of the members and these changes of relative stiffness in the structure induce redistribution of internal forces and the structure finally shows its ultimate strength.
A ship structure is composed of so many such members and its behavior to the ultimate strength is highly nonlinear. There are powerful tools to analyze nonlinear behavior, such as the finite element method, finite strip method, etc. However, the analysis by these methods requires enormous computing time for calculation and in the present circumstances it is impossible to apply these methods directly.
To overcome these difficulties, an analytical unit of large size and idealization of the highly nonlinear behaviors are developed in this paper. A “Girder Element” is proposed, of which stiffness matrices are derived for indivisual kinematic condition, such as after buckling, at the ultimate strength or plastic strength under compression, bending, and/or shear. Based on these idealized behaviors, a method of ultimate strength analysis is proposed. The result of analysis by this method represents well the detail behavior of example structures, of which simple one well coincides experimental behavior conducted in this study. The computing time is remarkably very short.
These nature of the new method promises the validity and possibility of the method to the ultimate strength analysis of structure of large size.