Flexural behaviour of concrete-filled stainless steel SHS and RHS tubes

This paper presents an experimental investigation on flexural behaviour of concrete-filled stainless steel square and rectangular hollow section (SHS and RHS) tubes under uniaxial bending. A total of 24 specimens including 16 concrete-filled stainless steel SHS and RHS flexural members and 8 empty stainless steel SHS and RHS flexural members were tested. The ultimate strengths, failure modes, flexural stiffness, ductility, bending moment-midspan deflection curves, overall deflection curves and strain distribution curves of test specimens are reported. It is demonstrated that the ultimate strength, initial stiffness and ductility of empty stainless steel SHS and RHS flexural members are significantly enhanced by filling the concrete in the specimen along its full length. The enhancement is increased with the increase of the thickness of the SHS and RHS tube. Furthermore, the concrete strength has little influence on the ultimate strength, initial stiffness and ductility of concrete-filled stainless steel SHS and RHS flexural members. The test flexural stiffness including both initial flexural stiffness and flexural stiffness at the serviceability limit state of concrete-filled stainless steel SHS and RHS tubes under uniaxial bending are compared with the design flexural stiffness calculated using the current AIJ standard, BS 5400, Eurocode 4 and AISC specification for concrete-filled steel tubes. It is shown from the comparison that the current design rules are all unconservative for initial flexural stiffness and flexural stiffness at the serviceability limit state of concrete-filled stainless steel SHS and RHS tubes under uniaxial bending with high scatter of predictions.