An investigation on the static mechanical property of concrete-filled steel square tubes under eccentric compression condition

Abstract

The static response of high-strength concrete-filled steel square tubes (CSST) under eccentric compression was examined through a three-dimensional nonlinear finite element model established in commercial software. In this study, CSST denotes a square-circular double-skin composite member made up of an outer square steel tube, an inner circular steel tube, and the concrete layer between them. After the model was checked against available load-deflection test results, it was used to assess the influence of outer-tube strength, inner-tube strength, concrete strength, and eccentricity ratio on the full-range mechanical response. The calculated response passes through elastic, elastic-plastic, and stable post-peak softening stages, showing that the member can retain a meaningful level of deformation capacity after the peak load. The post-peak behaviour depends on the interaction among concrete compression, restraint from the outer tube, and stress redistribution within the section. A stronger outer tube improves ductility, whereas the effect of inner-tube strength is relatively small. Higher concrete strength increases stiffness and resistance but usually weakens ductility, while a larger eccentricity ratio has the most adverse influence on both capacity and deformation performance. The results provide a numerical reference for support members required to work under combined compression and bending.