Axial compression performance and calculation model of GFRP tube-concrete-steel tube composite columns

This study systematically investigates the axial compression behavior of double-skin tubular short columns incorporating an external glass fiber-reinforced polymer (GFRP) tube, machine-made sand concrete, and an internal steel tube. Through axial compression tests on seven specimen groups with varying design parameters, the effects of GFRP tube thickness, hollow ratio, steel tube diameter-to-thickness ratio, and concrete core strength were examined. The results demonstrate a remarkable synergistic interaction among the constituent materials, enabling the composite columns to achieve an ultimate load capacity 1.27 to 2.05 times the sum of their individual nominal capacities. Among all parameters, GFRP tube thickness exhibited the most pronounced influence: increasing the thickness from 3 mm to 4 mm and 5 mm enhanced the ultimate load capacity by 32.2% and 58.3%, respectively. While reducing the steel tube diameter-to-thickness ratio from 16 to 8 improved load capacity, its effect on ultimate strain enhancement remained relatively limited. A predictive model for ultimate load capacity was developed using the superposition principle, comprehensively accounting for the lateral confinement contributions from both the GFRP and steel tubes. Validation against experimental results and existing literature data confirms the model’s high predictive accuracy.