Numerical Investigation of Structural Stress in Ship Cabins with Irregular Breaches Under Fire

Existing coupled fire–structure analyses for ships generally rely on idealised models with regular breaches and uniform material properties, neglecting heat-affected zone (HAZ) degradation at the breach edges (a term used here in a generalised sense), while the coupled stress mechanism remains poorly understood. In this study, large-eddy simulation with the Fire Dynamics Simulator (FDS) is combined with a sequentially coupled thermal–structural analysis in Abaqus. Equal-area breach models with a degraded HAZ band quantify the individual and coupled effects of HAZ degradation and breach-shape irregularity. The HAZ raises the stress concentration factor (Kt) by approximately 16% and shifts the peak stress location from the geometric corners to the weakened annular band. Under equal-area conditions, the combined HAZ and irregular polygon effects elevate Kt by about 71% relative to a rectangular breach without an HAZ, about 8% higher than the multiplicative superposition estimate. This synergy is significant only for highly irregular breaches with sharp re-entrant corners, whereas weakly irregular shapes conform to the independent-product assumption. An approximately linear relation between the shape irregularity index and Kt over nine equal-area shapes supports first-order screening estimates. The findings provide a screening framework for prioritising repair of fire-damaged ship cabins that remain within the elastic regime.