Concrete structures develop high levels of transient creep strain when exposed to fire, especially when temperatures in a member exceed 500°C. This high-temperature creep strain can dominate the deformation response under severe fire scenarios and needs to be properly accounted for in the fire resistance analysis. Most of the current approaches for fire resistance calculations, including advanced analysis methods, do not consider the transient creep strain to the full extent. This paper presents design recommendations for the treatment of creep in the fire resistance analysis of concrete structures. Three design alternatives are proposed for incorporating creep in fire resistance analysis depending on the conditions encountered during fire exposure. The first solution is ‘creep-not critical’ scenario where the temperature-induced creep strain can be neglected in a structural member subjected to low stress level and experiencing low sectional temperatures. In the second scenario (‘creep-implicit’), where temperature-induced creep strain is moderate, creep can be incorporated implicitly in the analysis. Finally, in situations where creep is significant (as in the case of high stress level and sectional temperatures), it needs to be incorporated explicitly in the fire resistance analysis (‘creep-explicit’ scenario). The practicality of the proposed solution in accounting for creep in the fire resistance analysis of concrete members at different levels is demonstrated using three case studies.

中文翻译：

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混凝土结构耐火分析中高温蠕变处理指南

混凝土结构在暴露于火中时会产生高水平的瞬态蠕变应变，尤其是当构件中的温度超过 500°C 时。这种高温蠕变应变可以在严重火灾情况下主导变形响应，需要在耐火分析中适当考虑。大多数当前的耐火计算方法，包括高级分析方法，都没有充分考虑瞬态蠕变应变。本文提出了在混凝土结构的耐火分析中处理徐变的设计建议。根据火灾暴露期间遇到的条件，提出了三种设计备选方案，用于将蠕变纳入耐火分析。第一种解决方案是“蠕变不临界”情形，在这种情况下，在承受低应力水平和经历低截面温度的结构构件中，温度引起的蠕变应变可以忽略不计。在第二种情况（“隐式蠕变”）中，温度引起的蠕变应变适中，蠕变可以隐式地包含在分析中。最后，在蠕变显着的情况下（如在高应力水平和截面温度的情况下），需要将其明确纳入耐火分析（“蠕变-显式”情景）。使用三个案例研究证明了所提出的解决方案在不同级别混凝土构件的耐火分析中考虑徐变的实用性。