FRP-confined circular concrete-filled steel tubular columns under cyclic axial compression

• An experimental study of CCFTs under cyclic axial compression is presented.
• CCFTs are shown to be very ductile under cyclic axial compression.
• Repeated loading cycles have a cumulative effect on confined concrete in CCFTs.
• An accurate cyclic stress–strain model for confined concrete in CCFTs is proposed.

Concrete-filled steel tubes (CFTs) are widely used as columns in many structural systems. In CFTs, inward buckling deformations of the steel tube are prevented by the concrete core, but degradation in steel confinement, strength and ductility can still result from outward local buckling. To overcome this deficiency of CFTs, CFTs can be confined with fibre-reinforced polymer (FRP) wraps to suppress outward local buckling deformations. This paper is concerned with the behaviour and modelling of FRP-confined concrete-filled steel tubular columns subjected to cyclic axial compression. Results from two series of cyclic axial compression tests on CCFTs are presented and discussed. A cyclic stress–strain model for confined concrete in CCFTs is also proposed and is shown to compare well with the test results. The proposed stress–strain model can be employed in the modelling of CCFTs under seismic loadings in future studies.