In order to accurately evaluate the longitudinal ultimate strength of a hull girder under the cyclic bending moment, the effects of an elastic-perfectly plastic and Chaboche material model on the elastic shakedown and ultimate strength of the hull girder under the cyclic bending moment are studied.

The nonlinear finite element method is used to carry out the ultimate strength numerical simulation of a double bottom bulk carrier considering the elastic shakedown under the cyclic bending moment. In this study, the Bauschinger effect of the material during the reverse loading of the structure and influence of the welding initial deformation and residual stress are considered.

The calculation results show that the welding initial deformation significantly reduces the lower limit of the elastic shakedown of bulk carrier, and the range of the elastic shakedown considering welding initial deformation and residual stress is the largest. After reaching the elastic shakedown under the cyclic bending moment, the ultimate strength of the bulk carrier considering the welding initial deformation and residual stress under hogging and sagging states are 7.15% and 5.68% higher than that under single loading respectively.

The welding initial deformation has a major impact on the elastic shakedown interval and elastic shakedown ultimate strength of the bulk carrier, which should be carefully considered in actual research and analysis.

The aim of this paper is to evaluate the longitudinal ultimate strength of a hull girder more accurately and determine its collapse process.

A bulk carrier is finely modeled in nonlinear finite element software ABAQUS, and the effects of slight, average, and severe welding initial deformations and average welding residual stress on the ultimate strength of the hull girder under hogging and sagging bending moments are fully considered.

The calculation results show that the hull girder's ultimate strength and bending stiffness decrease gradually with the increase of the initial deformation amplitude. Severe welding initial deformation makes the ultimate strength of the bulk carrier decrease by 14.25%, and the bulk carrier's ultimate strength decreases by up to 8.22% under the effect of welding residual stress individually. The combined effect of welding initial deformation and residual stress on the hull girder's ultimate strength is not a linear combination of the effects of the two initial deformations individually.

The combined effect of welding initial deformation and residual stress on a hull girder's ultimate strength should be considered more carefully in research on the ultimate strength of hull girders.