中文摘要：

采用合理的钢材和混凝土的热-力耦合本构模型，针对火灾下钢筋混凝土截面可能出现卸载和反向再加载情形，提出高温下混凝土单轴应力-应变滞回关系。根据火灾下U.L列式虚功增量方程和分层非线性梁单元方法，建立火灾下钢筋混凝土柱非线性有限元分析理论并编制相应的全过程分析程序NARCLF。对典型火灾下钢筋混凝土柱的试验资料进行双重非线性有限元分析。研究结果表明：采用材料应力一应变滞回关系的有限元分析方法的计算结果与实验结果较吻合，证明采用该方法可合理反映火灾下钢筋混凝土柱的变形特性和耐火性能。

英文摘要：

Applying appropriate thermal-stress coupling constitutive model of both steel bars and concrete in fire, considering that there would appear unloading and even reverse reloading, the stress-strain hysteretic relationship for concrete at high temperature was proposed. According to U.L. formula of element incremental equilibrium under fire condition and layered nonlinear finite beam element method, the analysis theory of nonlinear finite beam element for reinforced concrete （RC） columns in fire was presented and a FORTRAN program named NARCLF was developed. The reliability of the present method and program was validated by the experimental results of RC columns with rectangular section in fire. The results show that the analytical results are in good agreement with the experimental ones, which indicates that the present method and program based on stress-strain hysteretic relationship for material at high temperature can reflect the deformation and fire resistance behavior of the columns in fire reasonably.