热膨胀系数时变性对混凝土温度应力仿真影响

Effect of time-varying thermal expansion coefficient on thermal stress simulation of concrete

已有试验研究表明,混凝土的热膨胀系数具有明显的随龄期发展的特性.为了研究混凝土热膨胀系数时变特性,以及更好地模拟混凝土早龄期温度应力,分析热膨胀系数时变效应对混凝土温度应力仿真的影响,采用温度应力试验机进行试验,对混凝土热膨胀系数进行测定.引入等效龄期的概念,将混凝土早期变形分离为温度变形与自生体积变形,建立热膨胀系数与等效龄期之间的数学模型.通过室内试验试件的有限元数值模拟,验证热膨胀系数时变模型的合理性.将时变模型应用于大岗山特高拱坝施工期的温度应力仿真,通过对比研究,分析热膨胀系数时变效应对混凝土温度应力的影响.研究表明,混凝土热膨胀系数在早龄期变化较大,考虑其时变性对仿真防裂意义重大.尤其对于受通水等影响早期温降速率较快的混凝土,考虑热膨胀系数时变效应进行仿真计算应力水平较传统方法偏高,据此计算结果进行防裂设计更安全.

Previous studies have shown that the thermal expansion coefficient of concrete has obvious age-dependent characteristic.An experiment based on temperature-stress testing machine was designed to measure the thermal expansion coefficient,in order to study the time-varying characteristic of the thermal expansion coefficient of concrete and its effect on the thermal stress simulation,and to simulate the early-age temperature stress of concrete more accurately.The concept about the equivalent age was introduced.The temperature deformation and self-grown volume deformation were separated successfully.A mathematical model between the thermal expansion coefficient and the equivalent age was established.The rationality of this model was verified through the simulation of the laboratory test.Additionally,the effect of time-varying thermal expansion coefficient on temperature-stress simulation was discussed through the simulation of temperature-stress of Dagangshan super high arch dam.Results showed that the coefficient of thermal expansion of concrete changed greatly in early age.Considering the timevarying property of the coefficient of thermal expansion is significant for simulation and crack prevention.The simulated stress level calculated by considering the time-varying effect was higher than that of the traditional method,especially for the concrete with fast temperature drop rate at early age due to water flow.It is safer to carry out crack prevention design according to the new method.