Abstract This study aims to provide numerical formulation of the behavior of the compact concrete-filled steel tubes (CFSTs) based on constraints with the tie model permitting the two regions to fuse together. This study defined the interface between steel tubes and concrete cores with tie parameters allowing only rotation at the interface. Nonlinear finite element analyses were performed to explore the influence of tie and slip models on the flexural strength of concrete-filled steel tube members, resulting in improved predictions when the confinement provided by a steel tube was modeled with tie element. The passive confinement provided by the steel tube was hindered by the difference in the Poisson’s ratio between the steel tube and concrete when slip elements allowed for infinitesimal movement between a concrete core and steel shell. The numerical results were also consistent with results obtained by the modified strain compatibility-based simplified methods in which no relative motion was assumed between the steel tube and concrete core. The numerical results were well correlated with test data and codes supplied by prior researchers when the test specimens in which relative movement at interface between concrete core and steel jacket was infinitesimal or relative movement between interface between concrete core and steel jacket was not allowed for CFTs with shear connectors. Improved predictions by the tie model demonstrated higher accuracy compared with that of the slip models.