This paper describes the behaviour of large-length ships built using fibre-reinforced plastic compositematerials under fire and large deformations. A novel methodology is proposed in order to analyseinelastic buckling and post-buckling of steel structures due to thermal loading and also extend thisto the phenomenon regarded as pyrolysis that is natural in composite structures. The methodologyis validated against the literature. A model of a container-ship where a fire scenario located in theengine room is used to demonstrate the methodology against a real case scenario. The section of thecargo hold closest to the engine room is structurally analysed, focusing in the integrity of the bulkheadand the supports of the TEU containers.