Eccentric compression performance and computational modelling of GFRP tube-manufactured sand concrete-steel tube composite columns

In this study, to explore the eccentric compression behavior and computational model of GFRP tube-manufactured sand concrete-steel tube composite columns, 14 short columns with a diameter-height ratio of 1∶3 were tested under eccentric compression. The main parameters were eccentricity ratio (0-0.3), hollow ratio (0.48, 0.56) and concrete strength (C40, C50). Two bearing capacity calculation models were compared, and a simplified eccentric compression calculation model was studied based on the double-coefficient product law. Results indicate that when the eccentricity ratio is below 0.2, the composite columns have good collaborative force resistance, showing ductile failure concrete cracks, GFRP tubes fracture, and steel tubes bend. As the eccentricity ratio increases from 0.2 to 0.3, failure changes from ductile to brittle, with concrete and GFRP tube ends damaged and the steel tube's strength not fully utilized. An increasing eccentricity ratio reduces ultimate bearing capacity but enhances ductility. Raising the hollow ratio and concrete strength has limited effect on increasing ultimate bearing capacity under eccentric compression and reduces ductility. Ignoring the GFRP tube's axial strength leads to underestimated predictions. The established simplified calculation model can predict the composite columns' ultimate eccentric bearing capacity with a maximum error of less than 15%.