Effect of Confinement on Sustainable Concrete-Filled Steel Tubular Stub Columns Incorporating Recycled Waste Materials

This study investigated the axial compressive behaviour of sustainable concrete-filled steel tube (CFST) stub columns incorporating glass powder (GP) as a partial cement replacement and nitrile rubber (NR) gloves as additive fibres. A detailed finite element (FE) model was developed in Abaqus using the Concrete Damage Plasticity (CDP) model, in which modified constitutive relationships were adopted to account for the effects of GP and NR fibres. The numerical model was validated against 12 experimental stub columns. The validation showed that the predicted ultimate loads were within 4% of the experimental values, and that the load–axial strain behaviour and the failure modes showed good agreement with the experimental results. A comprehensive parametric study comprising 96 FE models was conducted to evaluate the influence of steel tube diameter, thickness, and yield strength, along with different GP and NR fibre contents. The results indicated that although the incorporation of GP and NR fibres reduced the compressive strength of unconfined concrete, steel confinement significantly compensated for this loss. The confinement effectiveness of steel tubes was found to be highly dependent on the diameter-to-thickness (D/t) ratio, with lower D/t ratios providing stronger confinement, enhanced ductility, and improved post-peak behaviour. Increasing tube thickness and steel yield strength markedly improved axial capacity, energy absorption, and confinement efficiency, whereas larger diameters increased strength but reduced ductility. A comparison with eight existing design codes and empirical models showed that several empirical models provided close predictions of the FE results, whereas some design codes either overestimated or underestimated the FE-derived axial capacity of CFST columns incorporating GP and NR fibre concrete. Overall, the study demonstrated that the combined use of GP and NR fibres in CFST columns is structurally viable when adequate confinement is provided. The findings contribute to a better understanding of the confinement behaviour of CFST columns incorporating GP and NR fibres and provide theoretical insights into their axial capacity prediction, while providing a foundation for the development of reliable material models for this novel sustainable concrete in composite structures.