火灾下圆钢管混凝土柱非线性有限元分析

首先提出合理的火灾下钢管混凝土拉、压材料数值热-力耦合本构模型及相应的计算方法;然后基于连续介质力学,推导火灾下U.L.列式虚功增量方程,采用非线性梁单元理论,给出火灾下钢管混凝土柱非线性有限元方程组的求解方法,编制非线性有限元程序NACFSTLF;最后对已有火灾下钢管混凝土柱的试验资料进行双重非线性有限元分析并考察钢管混凝土柱初始缺陷对其抗火性能的影响。分析结果表明:火灾下钢管混凝土柱的轴向变形-火灾时间曲线的计算结果基本上反映钢管混凝土柱的变形特性,而计算的耐火极限基本上是试验结果的上限;同时随着火灾下柱初始缺陷的增大,相同火灾时间下柱的跨中侧向挠度变形逐渐增大,耐火极限逐渐降低,而对柱的轴向变形影响相对较小。

Nonlinear finite element analysis of concrete filled circular steel tubular columns in fire

An 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.