Combined compression-bending-torsion behaviour of CFST columns confined by CFRP for marine structures

Abstract An innovative composite structural member formed by concrete filled steel tube (CFST) circumferentially confined by carbon fiber-reinforced plastics (CFRP), i.e., referred to as CFRP-CFST, has great potential to be used in marine environment due to its excellent structural performance and corrosion resistance. This paper aims to investigate the behaviour of CFRP-CFST subjected to combined compression-bending-torsion load. Quasi-static tests are conducted on 5 CFRP-CFST members and 3 reference bare CFSTs. The test parameters include the loading scenario (pure torsion, bending-torsion, and compression-bending-torsion), the axial load ratio and the layers of CFRP wrapping. Experimental results show that the CFRP-CFST members exhibit good energy dissipation capacity under pure torsion and compression-bending-torsion loads, while the applied axial force benefits the bearing capacity and the stiffness. However, ‘pinch’ effect is observed in the load-deformation hysteretic curves of CFRP-CFST under bending-torsion load. It indicates that the confinement provided by CFRP can significantly improve the column bearing capacity and ductility under torsion. When subjected to combined compression-bending-torsion, the CFRP wrapping can effectively improve the column ductility. The energy dissipation capacity increases with multiple CFRP layers. Eventually, the structural mechanism at the ultimate limit state is analyzed, with the calculation methods for the bearing capacities evaluated.