This article presents the fire Smith method, which integrates the plate model and the Smith method, to analyze the impact of fire temperature and extent on the buckling strength of frigates. This investigation focused on the frigate’s buckling strength and how it is affected by a fire, achieved by modifying both deck temperature and area. Leveraging the principle of oxygen consumption, a coefficient “D” was introduced to account for fire temperature and region variations. This enabled the characterization of buckling strength under varying temperature and regional conditions through 64 simulations conducted on a frigate model. The outcomes revealed that the disparity between simulation results and the fire Smith method remained below 10%, establishing a solid basis for engineering assessment. As the high-temperature area decreased and necessitated less oxygen, the ultimate strength initiated a decline. However, upon reaching a certain threshold temperature, the ultimate strength stabilized. Conversely, expansive high-temperature zones caused a decline in ultimate strength, coupled with an increased oxygen requirement. Under consistent oxygen consumption conditions, the rate of ultimate strength reduction intensified. Consequently, these divergent characteristics of ultimate strength in various high-temperature areas underscored that minimizing the expansive fire high-temperature zones can significantly enhance the ship’s fire resistance, safeguarding its structural integrity.

To evaluate the residual strength of the ship after explosion, the Explosion Smith Method (ESM) is proposed. The innovation of the ESM lies in two aspects: firstly, based on the Baker shock wave and quasi-static pressure model, Jones critical velocity model, propose a method for assessing the range of explosion damage of cabin and validated through referenced experiments. Secondly, proposes the strain-stress relationship of the deformation element. To verify the feasibility of the ESM and study the influence of TNT location and mass,16 simulations and EMS calculations were conducted. The results showed that the residual strength is most impacted when the TNT in top deck. For side cabin, the explosion products discharged and impact reduced. The trend of the ESM and simulation were consistent, but the result of ESM was more severe. The reason that strain-stress relationship of the deformation element more stringent, resulting in the ESM smaller than the simulation. However, as the TNT increases the error decreases. In the future, more research can be conducted on the deformed structures to enhance the accuracy of the ESM.

An easier and more efficient method is proposed for evaluating the ultimate strength of ship structures under fire conditions. Based on the Ideal Structural Unit Method (ISUM) and experiments from reference literature, a stress and strain equation for stiffened plates under fire conditions, as well as Fire ISUM, are proposed. To verify the effectiveness of the Fire ISUM method, 48 sets of FEA simulations incorporating the Fire ISUM were used to calculate the ultimate strength of different cabin fire positions and temperatures. The results showed that both the simulation and Fire ISUM were able to evaluate the high temperature ultimate strength. However, the Fire ISUM method does not account for initial imperfections due to the use of ideal high-temperature stress-strain curves. As a result, simulation results are lower than those obtained with the Fire ISUM, with a maximum error of 5.24%. To study the influence mechanism of ultimate strength of ship under high temperature conditions, the ultimate strength attenuation factor “I_UR” was defined. Simulation results show that the ultimate strength attenuation of different cabins is not only related to the high-temperature width but also to the distance between the deck and the neutral axis. In actual fire rescue processes, when a deck of the same area is subjected to high temperatures, the further the deck is from the neutral axis, the more important its protection.