Behaviour of hollow core square reinforced concrete columns wrapped with CFRP with different fibre orientations

• Effect of fibre orientation on the behaviour of hollow core columns was investigated.
• The columns were tested under different eccentricities.
• Fibres in the hoop direction significantly increased the ductility of the columns.

Results of testing twelve hollow core square reinforced concrete columns wrapped with Carbon fibre reinforced polymer (CFRP) are presented. The effect of fibre orientation on the performance of specimens under concentric and eccentric loads was investigated. Twelve specimens (200 mm × 200 mm in cross-section, 800 mm in height and having an 80 mm square hole) were divided into four groups with three specimens each. The specimens in the first reference group were unwrapped, while the specimens in the remaining groups were wrapped with CFRP of different wrap combinations of three fibre orientations (0°, 45°, and 90° with respect to the circumferential direction). The specimens in each group were tested under three eccentricities: 0 (concentric), 25, and 50 mm up to failure. Test results show that all wrapping configurations increased both the strength and ductility of hollow core square reinforced concrete columns. However, the increase of compressive strength was marginal. The columns, which were wrapped exclusively with hoop configuration, proved to have the greatest ductility. Axial load-bending moment P–M interaction diagrams of each group were drawn based on the experimental results and compared with theoretical calculations.