火灾下钢筋混凝土热弹塑性徐变本构方程研究

Research on a thermo-elastic-plastic creep constitutive equation for reinforced concrete subjected to fire

火灾高温作用下钢筋和混凝土材料的力学性能变化非常复杂.为了研究钢筋混凝土材料的抗火性能,基于热弹塑性徐变理论,考虑了材料性能随温度的变化,并根据不同的屈服法则,推导出了钢筋和混凝土材料热弹塑性徐变问题的增量本构方程.采用了向后Euler积分法和隐式积分的广义中心法,根据给出的求解步骤对推导得出的钢筋和混凝土热弹塑性徐变本构方程进行了数值模拟,所得结果与现有试验模型基本吻合.从计算结果可以看出,高温下钢筋混凝土材料的徐变应变是不可忽略的,并且随着温度的升高而升高.该研究为进行钢筋混凝土结构在火灾高温作用下的耐火性能分析提供了理论依据.

Changes in the mechanical performance of steel and concrete exposed to fire are complicated. Determining the fire resistance performance of reinforcement concrete based on the theory of thermo-elastic-plastic creep required the application of different yield rules. The incremental thermo-elastic-plastic creep constitutive equations of steel and concrete were derived in terms of changes in the properties of these materials with temperature. In the process of simulating the constitutive equation, algorithms providing backwards Euler integration and implicit inte- gration were adopted. The calculation results were basically consistent with experimental results. It was concluded from the numerical results that the creep strain of concrete at elevated temperatures can not be ignored and these values increased with rising temperatures. Thus a theoretical basis was developed for analysis of the fire-resistance of reinforced concrete structures exposed to fire.