Axial compressive behavior of coal gangue concrete-filled composite steel tube stub columns

Abstract

This paper presents a numerical investigation on the axial compressive behavior of composite steel tube coal gangue concrete (CG-CFCST) stub columns, in which an outer circular steel tube and an inner circular steel tube confine a sandwich layer of ordinary concrete and a core of coal gangue concrete. A three-dimensional finite element model is developed using the concrete damaged plasticity (CDP) model, validated in a stepwise manner against existing CFCST and CG-CFST test data, and then used to perform a systematic parametric analysis. The influence of key parameters-including the outer tube diameter-to-thickness ratio ( \(D/{t}_{o}\) ), the yield stresses of the outer and inner steel tubes ( \({f}_{yo}\) , \({f}_{yi}\) ), the inner tube diameter ( \({D}_{i}\) ), the inner tube diameter-to-thickness ratio ( \({D}_{i}/{t}_{i}\) ), and the compressive strength of the sandwich ordinary concrete ( \({f}_{cu,s}\) )-on the axial load–displacement response, von Mises stress in the steel tubes, longitudinal stress in the concretes, and steel–concrete interaction forces is examined. The numerical results indicate that \(D/{t}_{o}\) , \({f}_{yo}\) and \({f}_{cu,s}\) have a dominant influence on the shape of the N- \(\Delta\) curve, significantly affecting peak load and post-peak softening, whereas \({D}_{i}\) , \({D}_{i}/{t}_{i}\) and \({f}_{yi}\) mainly have a secondary influence, causing relatively small changes in peak load and the descending branch. For the interface between the inner steel tube and the core coal gangue concrete, whether the interaction force at mid-height is lower or higher than that at the column ends depends on the specific parameter values, while for the interfaces between the inner tube and the sandwich concrete and between the outer tube and the sandwich concrete, the interaction forces at the two ends are consistently higher than those at mid-height. The distributions of von Mises stress in the outer (inner) steel tube and the longitudinal stress in the sandwich ordinary concrete (core coal gangue concrete) also vary systematically with the studied parameters, reflecting a redistribution of axial load and confinement between the inner and outer tubes and between the sandwich and core concrete regions. Overall, the study is positioned as a finite element based numerical prediction and mechanistic exploration of CG-CFCST stub columns, and the reported trends and interaction mechanisms provide a reference for the design and future experimental research of such members.