This work reports the results of a numerical investigation aiming at assessing the structural safety of an actual offshore topside steel structure exposed to accidental localised fire conditions. Particularly, the paper explores the nonlinear thermomechanical and ultimate strength behaviours obtained by means of two fire approaches: sophisticated CFD (Computational Fluid Dynamics) and “LF-ESF” (Localised Fire with Ellipsoidal Solid Flame), previously developed and validated by the authors. CFD-based approaches, which typically solve nearly compressible flow with input energy given by a combustion model, allow accurate evaluation of a fluid-thermo response for the entire duration of the simulated accident. However, the analysis complexity, massive amount of produced data, excessive computational and time-consuming make CFD approaches unsuitable for the current applied design usage. On the other hand, the proposed LF-ESF approach displays quite accurate estimates in comparison to CFD counterparts. Moreover, the LF-ESF can be directly modelled in FE-based commercial software and used to obtain the steel temperature variation and thermomechanical behaviour. The obtained results indicate that the LF-ESF approach combined with FE-based models can provide reliable fire-safety analyses, ensuring that the main safety (load-bearing) functions of the offshore steel structures are not impaired during accidental fire conditions.

这项工作报告了一项数值研究的结果，旨在评估暴露于意外局部火灾条件下的实际海上顶层钢结构的结构安全性。特别是，本文探讨了由两种火焰方法获得的非线性热力学和极限强度行为：复杂的CFD（计算流体力学）和“ LF-ESF”（椭圆形固体火焰局部火焰），这是作者先前开发和验证的。基于CFD的方法通常使用燃烧模型提供的输入能量来解决几乎可压缩的流动，从而可以在模拟事故的整个过程中准确评估流体热响应。但是，分析的复杂性，产生的大量数据，过多的计算和费时的操作使CFD方法不适合当前的应用设计使用。另一方面，与CFD相比，拟议的LF-ESF方法显示出非常准确的估算值。此外，LF-ESF可以直接在基于FE的商业软件中建模，并用于获得钢的温度变化和热机械行为。所得结果表明，LF-ESF方法与基于FE的模型相结合可以提供可靠的火灾安全性分析，从而确保在意外火灾情况下不损害海上钢结构的主要安全性（承重）功能。LF-ESF可以直接在基于FE的商业软件中建模，并用于获得钢的温度变化和热机械性能。所得结果表明，LF-ESF方法与基于FE的模型相结合可以提供可靠的火灾安全性分析，从而确保在意外火灾情况下不损害海上钢结构的主要安全性（承重）功能。LF-ESF可以直接在基于FE的商业软件中建模，并用于获得钢的温度变化和热机械性能。所得结果表明，LF-ESF方法与基于FE的模型相结合可以提供可靠的火灾安全性分析，从而确保在意外火灾情况下不损害海上钢结构的主要安全性（承重）功能。