This paper introduces a numerical model to assess the thermomechanical behavior of offshore structures subjected to pool fires. The aim of this model is to improve the representation of fires in comparison with other existing models (e.g., nominal fire curves or zone modeling). The method proposed combines two-zone model—2ZM and a modified solid flame model—MSFM for calculating the convection and radiation portions of the heat transfer process between the fire and the structure. Thermal and mechanical analyses are performed sequentially using the commercial Finite Element Analysis software ABAQUS®. To assess the structure’s behavior, the transient temperature field resulting from the preceding thermal analysis is used together with pre-existing operating loads for the mechanical analysis. A pool fire in a tank barge is presented as a case study. Comparison of temperature and strain fields obtained with the method proposed to the results of other methods for assessment of the casualty indicates that the new model allows more realistic estimation of the temperature fields produced by the fire with relatively low computational costs.