A Simplified Method for Concrete-Filled Steel Tube Column Analysis

To construct a finite element model of concrete-filled steel tube column which is suitable to practical engineering analysis, a double-beam (DB) element is proposed. The element is made up of two coinciding beams which simulate steel tube and kernel concrete respectively. The parameters analysis results show that a concrete-filled steel tube column should be divided into four or more DB elements to make the error of fundmental frequency less than 5%. Moreover, based on design codes of the concrete structures and steel-concrete mixed structure of tall buildings, a simplified constitutive model of kernel concrete is developed to consider the confinement effects of steel tube on the concrete. The results of numerical example show that the P-△ curve based on the simplified model is consistent with the experimental results, but the ultimate bearing capacity is less than experimental results. Therefore, the model has a reasonable reliability and can be a reference for similar engineering design analysis.