火灾下圆钢管混凝土柱非线性有限元分析

n appropriate numerical thermal-stress coupling constitutive model of both steel tube and concrete core and its calculation method in concrete filled circular steel tubes in fire were proposed in this paper. Then, based on the principles of continuum mechanics, the U.L. formula of element incremental equilibrium under fire condition was deduced. Applying the theory of nonlinear finite beam element, the solving method of nonlinear equilibrium equations for concrete filled steel tubular (CFST) columns in fire was presented and a FORTRAN program named NACFSTLF was developed. The reliability of the present method and program was validated by the experimental results of CFST columns in fire and the influence of initial defect of the column on the fire performance was discussed. 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; as the initial defect of the column in fire increased, the lateral deflection at mid-span of the column reached a higher value under the same exposure time and the fire resistance of the column decreased gradually, but the influence of axial deformation of the column was relatively small.