Flexural behaviour of concrete-filled aluminium alloy thin-walled SHS and RHS tubes

This paper presents an experimental study on flexural behaviour of concrete-filled aluminium alloy thin-walled square and rectangular hollow section (SHS and RHS) tubes subjected to in-plane bending. A total of 30 specimens including 20 concrete-filled aluminium alloy tubes (CFAT) and 10 bare aluminium alloy tubes (BAT) were tested. The ultimate strengths, failure modes, flexural stiffness, ductility, bending moment-midspan deflection curves, overall deflection curves, bending moment-longitudinal strain curves and longitudinal strain distribution curves of test specimens are reported. It is demonstrated that the ultimate strength, flexural stiffness and ductility of the BAT specimens are significantly enhanced by filling the concrete in the specimen along its full length. Furthermore, the enhancement is increased with the increase of the concrete strength, but the increase of enhancement is insignificant. The measured flexural stiffness including both initial flexural stiffness and post-yield flexural stiffness were compared with the design flexural stiffness calculated using the current AIJ standard, BS 5400, Eurocode 4 and AISC specification. It is shown from the comparison that the current design rules for the bare steel tube (BST) and concrete-filled steel tube (CFST) are generally inappropriate for the flexural stiffness of the BAT and CFAT under pure in-plane bending with high scatter of predictions. Furthermore, the design equations were proposed for the ultimate strengths of CFAT under in-plane bending, which were verified to be applicable.