Objective A heavy icebreaker may experience a certain degree of permanent deformation in its ice-strengthened structure after encountering over-designed ice loads. It is necessary to assess the residual strength of the ice-strengthened structure after permanent deformation to ensure navigation safety.

Method The ice-strengthened structure at the midship side of a heavy icebreaker is selected for a model test. A plate frame model is constructed using EH500 steel. High strength gypsum powder is used as the main raw material to make the non-refrigerated breakable model ice through mixing and pouring. First, the weak and strong members of the plate frame model are dynamically impacted by the free-fall of the model ice, causing permanent deformation in the test plate frame. Then, a quasi-static bearing test is conducted by loading on the weak members of the permanently deformed plate frame model until plastic collapse occurs, and the residual strength is measured. Finally, the entire dynamic impact test process is simulated using numerical methods to determine the permanent deformation of the specimen. The residual strength of the ice-strengthened structure is obtained through the explicit dynamic nonlinear analysis and compared with the experimental results.

Results The tests and calculations show that the maximum permanent deformation of the plate specimen is 33.11% larger when impacted on the weak component compared to the strong component when the ice-like test block with the same height falls freely. This results in a 3.28% reduction in the residual strength of the ice-strengthened structure. The comparison shows that the error between the experimental results and the numerical solutions is within 20%, indicating that the tests and numerical calculations are reasonable and credible.

Conclusion The research results reveal the effects of permanent deformation on the residual strength of the strong and weak members of the ice-strengthened structure of heavy icebreakers, as well as the failure modes at the limit state. These findings can provide a reference for the structural design and strength assessment of heavy icebreakers.