Structural behaviour of UHPC-filled double-skin aluminium columns under combined loadings conditions

Concrete-filled double-skin tubular columns are highly valued in modern construction for their outstanding load capacity, reduced self-weight, and excellent ductility. Replacing the steel tubes with lightweight aluminium alloys further enhances the strength-to-weight ratio and corrosion resistance. This study investigates both experimentally and numerically the axial and flexural behaviour of ultra-high performance concrete-filled double-skin aluminium circular tube columns. Five specimens were fabricated having a constant cross section with an outer diameter of 203.2 mm and an inner diameter of 80 mm. Four columns have been loaded under axial compression with varying eccentricities from 0 mm to 90 mm and a beam has been tested under four-point bending. The axial load capacity, failure pattern, load-deflection relationships, and load-strain relationships observed from the experimental program are reported. The finite element model (FEM) was developed and validated against the test results, and it was utilised to perform a parametric study examining the effect of concrete compressive strength, inner and outer tube thicknesses, and hollow ratio on the structural performance of the composite columns.