Behaviour and confinement mechanism of circular concrete-filled aluminum alloy tubular stub columns under axial compression

Concrete-filled steel tubes are widely applied in offshore structures, which often being exposed to aggressive ocean climate. This has recently led to the introduction of concrete-filled aluminum alloy tubular (CFAT) columns, of which aluminum alloy tube is used as a superior anti-corrosion metal material. However, limited research has led to the design of CFAT columns not being included in the current design specifications, limiting their engineering applications. Accordingly, in this paper, an experimental program including 9 CFAT specimens was launched to further investigate the compressive behavior of CFAT short columns and to clarify the confinement mechanism in such columns. The test results indicate that the ultimate capacity of CFAT short columns is improved with the increase of concrete strength or the decrease of tube diameter-to-wall thickness ratio. Based on the experimental results, the finite element model (FEM) was established, and then used to clarify the confinement mechanism of CFAT columns and investigate the effects of the salient parameters on the behavior of such columns. By comparing with the existing experimental results, the accuracy of current strength calculation formulas for CFAT columns was assessed, and the conclusion indicates that there is an unexpected deviation in the prediction results. To this end, a simplified strength prediction formula for CFAT columns was proposed, which successfully introduced a novel confinement factor that well reflects the confinement effect of the concrete core. This confinement factor considers the effects of proof stress, concrete strength, and tube diameter-to-wall thickness ratio. Finally, compared with other formulas, the proposed formula has better performance in predicting results.