Study on nonlinear dynamic response of four-tier multi-stack under different lashing failure modes

As container ships continue to grow in size, the instability of stacks caused by lashing system failures under dynamic sea conditions has become a primary cause of cargo losses at sea. However, current classification society regulations for the research on dynamic failure mechanisms in lashing systems remain insufficient, particularly concerning the nonlinear response characteristics under multi-stack coupling. A multi-stack dynamic test system, constructed based on Froude similarity principles, is employed to analyze the dynamic responses of displacement and acceleration within the system’s internal structure. The focus lies on the evolution characteristics of collision energy dissipation between stacks, load transfer path reconstruction, and nonlinear dynamic responses during the progressive failure of lashing rods. The findings indicate that nonlinear factors such as twist-lock gaps, corner casting contact, and friction can induce phase differences in motion between double-stacks, leading to reduced acceleration coherence between adjacent stacks. Lashing failure further exacerbates asymmetric collisions between double-stacks, resulting in complex coupling features in top container displacement and acceleration. Additionally, internal lashing failure shifts load distribution from vertical transmission to lateral diffusion, while external lashing failure is more likely to trigger lateral load transfer within, causing the dynamic tensile force in bottom lashing rods to enter a high-risk zone, thereby initiating a chain reaction of corner casting sliding-separation-collision. This research provides quantitative evidence for dynamic failure warning and redundant lashing design in multi-stack securing systems, addressing gaps in current standards regarding the assessment of dynamic failure modes.