A confined concrete model considering strain gradient effect of CFST column under eccentric load

Abstract

This paper analyzes the axial and eccentric compression mechanisms of concrete-filled steel tube (CFST) columns and proposes a confined concrete constitutive model that considers gradient effects. The model is based on the gradient effect of stress and strain under eccentric compression to deduce the gradient effect of confinement force, and obtain the calculation formula of confinement force under different eccentricities, so as to obtain the corresponding constitutive model of confined concrete. The model is used to modify the fiber model and Chinese Codes, which are affected by loading eccentricity. Six sets of CFST material constitutive test data are collected to validate the constitutive model. Eight sets of moment-curvature curves of section tests and twelve sets of eccentric compression bearing capacity tests were collected for validation. The data collected from these two sets of experiments were compared with the modified calculation values of the fiber models and the design codes, respectively, to confirm the reliability of the modification effect. The results indicate that the utilization of the model proposed in this paper successfully reflects the influence of eccentric loading on the confined concrete constitutive relationship, improves the prediction accuracy of existing formulas, and facilitates the analysis efficiency of CFST.