Liangli Xiao, Zhiwei Tan, Fanqiang Sun
This study aims to elucidate the synergistic action of steel and polyvinyl alcohol (PVA) hybrid fibres in glass fibre-reinforced polymer (GFRP)-reinforced concrete columns and to develop a reliable prediction model for axial compressive capacity. Axial compression tests were performed on nine specimens: eight hybrid fibre-reinforced GFRP concrete columns with varied fibre dosages and one conventional steel-reinforced control column. Failure modes, load–displacement behaviour and strain responses of longitudinal reinforcement, transverse reinforcement and concrete were compared across mixtures. Fibre-free GFRP columns exhibited sudden, brittle failure. Steel fibres primarily enhanced ultimate capacity; at 1.4% and 0.8% volume fractions, ultimate loads increased by 17.1% and 13.7%, respectively, relative to the steel control and by 24.7% and 21.1%, respectively, relative to the fibre-free column. However, excessive steel fibre content (>1.4%) caused poor dispersion and weaker fibre–matrix bonding, reducing reinforcement efficiency, axial displacement at peak load and overall ductility. In contrast, PVA fibres improved post-peak deformation and energy absorption, and hybridisation provided stable, balanced performance gains. Based on the experimental data set, relevant design codes and micromechanical interpretation, an optimised ultimate-capacity formula is proposed, showing good agreement with the measured results. The model offers a practical basis for design of hybrid-fibre GFRP columns.