Study on axial compression mechanical properties of circular carbon steel-concrete‑aluminum alloy composite columns

To evaluate the axial compression performance of circular carbon steel-concrete‑aluminum alloy composite columns, the axial compression test of 8 specimens was carried out, the parameters involved in the test mainly included the cross-sectional diameter, concrete type (normal concrete and lightweight concrete), and the wall thickness of the aluminum alloy tube. Subsequently, the failure modes, load-strain curves, lateral deformation coefficients, and load-axial displacement curves of the specimens were analyzed, clarifying the influence of variations in experimental parameters on bearing capacity, axial compression stiffness, and ductility. A full-scale finite element model was established by using ABAQUS to study the stress distribution of typical specimens. The influence degree and rules of various parameter changes on the axial compression mechanical performance indicators were analyzed and summarized, and furthermore, the equation for determining axial compressive strength for circular carbon steel-concrete‑aluminum alloy composite columns was proposed. The research results show that the deformation of components of specimen is consistent under axial compression load. The change in cross-sectional size have a notable effect on the axial compression mechanical performance indicators, when the cross-sectional size increases from 200 mm to 300 mm and 400 mm respectively, the bearing capacity of specimens with normal concrete (lightweight concrete) as sandwich concrete increases by 135.9 % and 329.3 % (91.6 % and 204.7 %), the axial compression stiffness increases by 1.93 times and 9.14 times (1.69 times and 8.0 times), and the ductility decreases by 30.3 % and 38.4 % (33.3 % and 40.1 %) respectively. Through conducting simulations with finite elements, the finding is that before reaching the ultimate bearing capacity, there is almost no interaction between the aluminum alloy tube and the sandwich concrete, while the contact stress between the steel tube and the sandwich concrete gradually increases with the increase of axial displacement, suggesting that the steel tube exerts a good confinement influence on the sandwich concrete. The calculation method of bearing capacity proposed based on the technical specifications for concrete-filled steel tubular structures and the introduction of the combined strength influence coefficient can reasonably predicted the axial compression bearing capacity of circular carbon steel-concrete‑aluminum alloy composite columns.