Structures need to be designed to maintain their stability in the event of a fire. The travelling fire methodology (TFM) defines the thermal boundary condition for structural design of large compartments of fires that do not flashover, considering near field and far field regions. TFM assumes a near field temperature of 1200°C, where the flame is impinging on the ceiling without any extension and gives the temperature of the hot gases in the far field from Alpert correlations. This paper revisits the near field assumptions of the TFM and, for the first time, includes horizontal flame extension under the ceiling, which affects the heating exposure of the structural members thus their load‐bearing capacity. It also formulates the thermal boundary condition in terms of heat flux rather than in terms of temperature as it is used in TFM, which allows for a more formal treatment of heat transfer. The Hasemi, Wakamatsu, and Lattimer models of heat flux from flame are investigated for the near field. The methodology is applied to an open‐plan generic office compartment with a floor area of 960 m² and 3.60 m high with concrete and with protected and unprotected steel structural members. The near field length with flame extension (fTFM) is found to be between 1.5 and 6.5 times longer than without flame extension. The duration of the exposure to peak heat flux depends on the flame length, which is 53 min for fTFM compared with 17 min for TFM, in the case of a slow 5% floor area fire. The peak heat flux is from 112 to 236 kW/m² for the majority of fire sizes using the Wakamatsu model and from 80 to 120 kW/m² for the Hasemi and Lattimer models, compared with 215 to 228 kW/m² for TFM. The results show that for all cases, TFM results in higher structural temperatures compared with different fTFM models (600°C for concrete rebar and 800°C for protected steel beam), except for the Wakamatsu model that for small fires, leads to approximately 20% higher temperatures than TFM. These findings mitigate the uncertainty around the TFM near field model and confirm that it is conservative for calculation of the thermal load on structures. This study contributes to the creation of design tools for better structural fire engineering.

中文翻译：

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火焰扩展和天花板下方的近场，用于在大隔间内行进燃烧

需要设计结构以在发生火灾时保持其稳定性。考虑到近场和远场区域，行进式火学方法（TFM）定义了不会闪络的大火室结构设计的热边界条件。TFM假定近场温度为1200°C，在该温度下火焰没有任何扩展地撞击在天花板上，并根据Alpert相关性给出远场中的热气体温度。本文重新审视了TFM的近场假设，并首次包括了天花板下方的水平火焰扩展，这会影响结构构件的热暴露，从而影响其承载能力。它还以热通量而不是TFM中使用的温度来表示热边界条件，这样可以更正式地处理传热。针对近场研究了火焰的热通量的Hasemi，Wakamatsu和Lattimer模型。该方法适用于面积为960 m的开放式通用办公隔间混凝土高度分别为²和3.60 m，带有受保护和不受保护的钢结构构件。发现具有火焰扩展（fTFM）的近场长度是没有火焰扩展的近场长度的1.5至6.5倍。暴露于峰值热通量的持续时间取决于火焰长度，对于5％地面缓慢着火的情况，fTFM为53分钟，而TFM为17分钟。使用Wakamatsu模型，大多数火势的峰值热通量为112至236 kW / m ²，而Hasemi和Lattimer模型的峰值热通量为80至120 kW / m ²，相比之下，则为215至228 kW / m ²用于TFM。结果表明，在所有情况下，与WFM型号相比，与不同的fTFM型号（混凝土钢筋为600°C，受保护钢梁为800°C）相比，TFM导致更高的结构温度。温度比TFM高％。这些发现减轻了TFM近场模型周围的不确定性，并确认对于结构上的热负荷计算是保守的。这项研究有助于创建用于更好的结构消防工程的设计工具。