Numerical modeling of octagonal concrete-filled steel tubular short columns accounting for confinement effects

Abstract

The concrete confinement induced by the steel tube of a concrete-filled steel tubular (CFST) column depends on its cross-sectional shape. The mechanism of confinement in octagonal CFST columns differs considerably from that in circular or square CFST columns. It is therefore important to ascertain the confinement effect in octagonal CFST columns to accurately quantify their behavior. In this paper, a numerical modeling method employing the theory of fiber analysis is presented that can simulate the axial behavior of short octagonal CFST columns that are loaded axially to failure. New constitutive laws of concrete including lateral confining stress model and the residual strength factor for compressive concrete in CFST octagonal columns are developed by interpreting the available test data. The concrete material model is implemented in the computational procedure of nonlinear analysis. The accuracy of various models of lateral confining stresses including the proposed one in this paper is evaluated against test data. The behavior of octagonal CFST stub columns including salient parameters is examined by using the computer program developed. A design equation is suggested for estimating the capacities of octagonal CFST stub columns considering confinement effects. The codified design methods in several international standards for circular CFST columns are evaluated against the test results to investigate their applicability to octagonal CFST columns. The developed material models and computational and design methods are shown to yield computations which are compared well with experimental results of octagonal CFST columns. The current design codes considerably underestimate or overestimate the strengths of octagonal CFST columns.