<p>Concrete-filled steel tube (CFST) columns have been extensively adopted in modern infrastructure due to their superior strength, stiffness and ductility arising from the synergetic interaction between the steel tube and the concrete core. Among the various geometries, tapered CFST columns have gained attention for their architectural appeal and spatial efficiency. However, their non-uniform confinement behaviour remains inadequately understood. This study experimentally and numerically investigates the axial compression behaviour of straight and tapered CFST columns. Twelve specimens including hollow steel tubes and CFST columns filled with either normal concrete (NC) or expansive fibre-reinforced concrete (EFRC) were tested to evaluate the influence of taper angle and concrete type on the confinement mechanism, strength, and ductility. Finite element models were developed in ABAQUS and validated against the experimental findings. Typical failure modes, load-displacement responses, and strain developments are presented and discussed to provide a deeper understanding of the role of non-uniform confinement on the structural behaviour. The results demonstrate that the use of expansive concrete enhances the confinement effect and overall performance of tapered CFST columns. Based on the results, a simplified analytical approach is presented for predicting the load-carrying capacity of tapered CFST columns under axial compression.</p>