Strengthening of steel members in compression by mortar-filled FRP tubes

A strengthening approach to improve the buckling resistance of steel members in compression is introduced in this paper, where a mortar-filled FRP tube is sleeved outside the steel member and wrapped with FRP fabrics at the ends of the tube. Through axial compression tests on 18 specimens with bi-axial symmetrical cross-section, the load–strain development and failure modes were obtained and improved load bearing capacity and ductility were evidenced. The effects of the cross-section of core steel, slenderness and FRP fabric layers wrapped at the ends of specimens were investigated. It was found that, after strengthening, the failure modes changed from steel yielding at the mid-height of the steel member due to global buckling to local damage at the steel end. As a result, the load bearing capacity increased by 44–215% and ductility increased by up to 877%. The segmentation model was developed for strengthened specimens, by which the calculated load bearing capacity agrees well with the experimental result.