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

This paper presents the experimental and numerical investigations on concrete-filled stainless steel square and rectangular hollow section (SHS and RHS) tubes subjected to in-plane bending. A total of 32 specimens were tested, in which one fourth of test specimens were unstrengthened for comparison. The ultimate strengths, failure modes, flexural stiffness, ductility and longitudinal strains of test specimens are reported. The corresponding finite element analysis (FEA) was also performed and calibrated against the test results. An extensive parametric study was carried out by using the verified finite element model to investigate the strengthening effect of CFRP on the flexural behaviour of concrete-filled stainless steel SHS and RHS tubes. It is shown from the comparison that the strengthening effect of CFRP was improved with the increase of the β value. Whereas, the ductility ratio was greatly deteriorated. Furthermore, the secant stiffness at 0.6Mu was recommended to be the flexural stiffness of concrete-filled stainless steel SHS and RHS tubes strengthened by CFRP in the practical applications. On the other hand, the flexural strength and flexural stiffness of concrete-filled stainless steel SHS and RHS tubes were increased with the increase of interface friction coefficient between stainless steel tube and concrete up to 0.6. The design formulae are also proposed for the flexural strengths and flexural stiffness of concrete-filled stainless steel SHS and RHS tubes strengthened by CFRP based on the current design rules for concrete-filled steel tubes by further considering the flexural strengths and flexural stiffness of the CFRP, which were verified to be accurate by the finite element analysis results.