Stress-strain models of elliptical concrete-filled steel tube columns for direct analysis method

The accurate material constitutive model is the premise of realizing direct analysis method of structures, but the model for elliptical concrete-filled steel tube (CFST) structures has not been proposed yet. According to previous experiments of the research group, the development laws of the longitudinal stress-strain curves of steel tube and concrete in elliptical CFST columns were studied in this paper. Based on the characteristics of biaxial stress of steel tube and triaxial stress of core concrete, the longitudinal stress-strain models of steel tube and core concrete considering the effect of aspect ratio were suggested, respectively. Furthermore, on the basis of the proposed stress-strain relationships of steel tube and concrete, the load-deformation curves of the elliptical CFST column were established according to the static equilibrium condition and deformation compatibility condition. The theoretical load-displacement curves are verified well with test results. Also, axial compressive capacities of elliptical CFST columns are similar to experimental values and calculated values according to specifications GB 50936-2014 and EC4. The constitutive models of elliptical steel tube and concrete proposed in this paper are proved to be accurate, which can recommend for the structural design of elliptical CFST structures based on the direct analysis method. © 2021, Editorial Office of Journal of Building Structures. All right reserved.