A new method for assessing the shakedown limit state associated with the breakage of a ship's hull girder

Abstract

Shakedown occurs when a structure responds steadily under cyclic loadings within appropriate limits after one or a few cycles of loading. This study proposes a new method for assessing the shakedown limit state associated with the breakage of a ship's hull girder, considering the buckling effects seen under the cyclic hull girder actions of hogging and sagging bending. The method is applied to a Suezmax-class double-hull oil tanker as an example. The shakedown limit state of the ship under cyclic hull girder actions is analysed, and the results are compared with the ultimate hull girder strength of the ship under monotonically applied hull girder loads. It is concluded that a ship's hull under cyclic actions of vertical bending can collapse, with a shakedown failure even if the vertical bending moments applied are smaller than the ultimate hull girder strength determined under monotonically applied hull girder loads. The method and insights developed will be useful for assessing hull girder breakage subject to cyclic hull girder bending moments.