An analytical model for axially compressed circular concrete-filled steel tubular (CFST) short columns with varied confinement factors

Accurate evaluation of the load-strain behavior of axially compressed concrete-filled steel tube (CFST) short columns is pivotal for engineering structures, and depends on precise prediction of the hoop-axial strain response. This study introduces a two-stage hoop-axial strain relationship that incorporates the initial Poisson's ratio and elastic limit to account for the initial linearity of concrete, and a reduction coefficient to take into account the effect of concrete strength on lateral deformation properties, based on a widely used hoop-axial equation. Experimental validation across a definite concrete strength range of 28 MPa to 125.3 MPa reveals improved predictions for the dilation rate of CFST columns subjected to axial compression, particularly for those columns fabricated with high-strength concrete (> 100 MPa). Subsequently, an analytical model consisting of the proposed two-stage strain relationship, a confined concrete model with inflection-point strain and residual strength, and the biaxial stress-strain relationship of steel tube is then established to estimate the compressive behavior of circular CFST short columns. Experimental verification over a range of confinements (confinement factor from 0.289 to 2.138) demonstrates the ability of the proposed analytical model to accurately capture the load-strain curves of circular CFST short columns, especially the post-peak behavior of those with confinement factors less than 1. The performance of the established analytical model in assessing the axial load-carrying capacity of circular CFST stub columns is investigated using a database assembled from available studies.