Axial performance of concrete-filled GFRP tube columns jacketed by outer stainless steel tube and sandwiched concrete

The concrete-filled FRP tube (CFFT) column, a prevalent and crucial structural element in marine environments, requires reinforcement measures to enhance its operational performance. This paper introduces a novel strengthening technology involving sandwiched concrete and stainless steel tube jackets. By conducting axial compression tests on two CFFT columns and nine reinforced columns, the failure modes, load-axial deformation curves, and load-strain relationships were analysed in this study. Additionally, the influence of outer steel tube thickness (3.0 mm, 4.0 mm, 5.0 mm) and sandwiched concrete strength grades (C50, C60, C70) on the axial compressive performance of the reinforced columns was investigated. The findings indicated that the proposed reinforcement method effectively mitigated the brittle failure associated with the original CFFT column. The external stainless steel tube played a crucial role in restraining lateral deformation of the internal CFFT column, thereby enhancing the axial compressive bearing capacity. Through theoretical analysis on the components in reinforced columns, a calculation formula for the axial compressive capacity of the reinforced column was derived according to the unified theory and the double-shear unified strength theory.