火灾下钢筋混凝土柱非线性有限元分析

n analysis theory of nonlinear finite beam element for reinforced concrete (RC) columns in fire was presented and a FORTRAN program named NFEMRCLF was developed in this paper. First, the stress-strain hysteretic relations for concrete at high temperature was proposed and appropriate thermal-stress coupling constitutive model of both steel bars and concrete in fire were presented. What’s more, based on the U.L. formula of element incremental equilibrium under fire condition and the theory of nonlinear finite beam element, the solving method of nonlinear equilibrium equations for RC columns in fire was presented. Finally, the reliability of the analysis theory and program was validated by the experimental results of RC columns with rectangular section in fire, showing that the analysis results are in good agreement with the experiment results from references. From the results, it is indicated that the calculated results of axial deformation versus exposure time of the columns in fire reflected the deformation of them basically, and the calculated fire resistance of the columns was the upper bound of the test results in substance; the calculated results based on stress-strain hysteretic relations of both steel bars and concrete were more reasonable than that based on stress-strain skeleton relations.