Influence of Confinement Interaction on the Compressive Behavior of Steel Tube–Reinforced Concrete Columns

Abstract

A steel tube–reinforced concrete (ST-RC) column is composed of the inner concrete-filled steel tube (CFST) component and peripheral reinforced concrete (RC) component. In this study, the confinement interaction mechanism of axially loaded steel tube–reinforced concrete columns (ST-RC) was evaluated experimentally and analytically. Eleven column specimens were tested, including five ST-RC, three CFST, and three RC columns. The test results found that the confinement interaction between core CFST and outer RC components integrates both advantages while remarkably altering the section equilibrium and confinement mechanism compared with conventional confined concrete. Specifically, the following two aspects need to be considered. First, since the core CFST component is subjected to the secondary confinement provided by outer stirrups, the capacity of an ST-RC column is 1.07–1.21 times greater than that of the simple superposition of CFST and RC components (CFST+RC). Second, for the outer RC component, because the filled-in concrete is confined by the steel tube, the outer stirrups confinement cannot be effectively activated due to the weakened dilation of concrete. Such strain-lagging leads to a steeper falling branch of the load–axial strain curve of the ST-RC column under compression than that of CFST+RC. Finally, based on two modified constitutive models considering the confinement interaction mechanism in the ST-RC column, a well-defined analytical model for predicting the structural performance of axially loaded ST-RC columns was established.