A novel theoretical model capable of quantifying the stress causing transient thermal strain (TTS) in heated concrete is presented. It is applicable to numerical models and as a design equation for assessment of stress caused by combined actions of loading, heating fluxes and end restraints during heating. Three categories of concrete members are classified: heated then loaded; loaded then heated; heated with full restraint with or without load. The TTS equation is incorporated in a novel thermo-mechanical finite element model developed in ABAQUS. Material models capable of capturing degradation of concrete properties under elevated temperatures have been selected and adapted to include TTS and temperature dependence. The finite element model and stress equation have been successfully validated against experimental results under various loading configurations and boundary conditions. A number of observations were made: (i) stress developed under restraint is lower than under applied preload, but stress relaxation, in part owing to TTS, is higher under preload; (ii) the limit of elastic behaviour is reduced under free thermal expansion compared with restrained samples; (iii) free thermal expansion is critical to the overall stress–strain response and appears to vary with applied stress while significantly increasing at high temperatures.

中文翻译：

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直接预测高温下混凝土应力的广义模型

提出了一种能够量化在加热混凝土中引起瞬态热应变 (TTS) 的应力的新型理论模型。它适用于数值模型，并作为设计方程来评估由加热过程中的载荷、热通量和端部约束的联合作用引起的应力。混凝土构件分为三类：加热后加载；加载然后加热；带或不带负载完全约束加热。TTS 方程包含在 ABAQUS 中开发的新型热机械有限元模型中。已经选择并调整了能够捕获高温下混凝土性能退化的材料模型，以包括 TTS 和温度依赖性。有限元模型和应力方程已根据各种加载配置和边界条件下的实验结果成功验证。进行了一些观察：（i）在约束下产生的应力低于施加预紧力，但应力松弛，部分由于 TTS，在预紧力下更高；( ii ) 与约束样品相比，自由热膨胀下的弹性行为极限降低；( iii ) 自由热膨胀对整体应力-应变响应至关重要，并且似乎随着施加的应力而变化，同时在高温下显着增加。