Experimental study on axial load-bearing capacity of grout-lifted compressible concrete-filled GFRP tube composite column

To address the challenges of roadway along gob support under high-stress conditions, a grout-lifted compressible GFRP (Glass Fiber Reinforced Plastic) tube concrete composite support column structure was proposed. Axial compression tests were conducted on GFRP tube concrete composite columns with varying upper tube materials, diameter-to-thickness ratios, and pressure-relief displacements. The mechanisms influencing the load-bearing performance of the columns, including upper tube material, tube diameter, and pressure-relief structure, were systematically analyzed. Composite support column exhibits low unit weight, low material cost, strong corrosion resistance. Based on load-displacement curves, load-strain curves, and failure characteristics, the load-bearing capacity and pressure-relief performance of different types of columns were compared.The test results indicate that the grout-lifted compressible GFRP tube concrete composite support column exhibits an "enhanced resistance and pressure-relief" performance, and good coupling between the pressure-relief structure and the core concrete. For composite columns with GFRP tubes of ø220 mm×10 mm, ø270 mm×10 mm, and ø320 mm×10 mm under the same slenderness ratio, the ultimate load-bearing capacity ranges from 2180 kN to 3310 kN, and the ultimate pressure-relief displacement ranges from 171 mm to 235 mm, reaching 66%–90% of the initial pressure-relief structure height (260 mm). Both the ultimate load-bearing capacity and pressure-relief displacement increase with the GFRP tube diameter.To optimize the load-bearing structure of the composite column, steel tubes were used as the upper tube material. For the GC–1 and GC−2 columns, the ultimate load-bearing capacities are 2790 kN and 2830 kN, respectively, and the ultimate pressure-relief displacements are 190 mm and 195 mm. The compressible GFRP-steel tube concrete composite support column demonstrated superior load-bearing performance and failure characteristics compared to the compressible GFRP tube concrete composite support column. The load-bearing performance of the composite column increases with the wall thickness of the steel tube.Based on the deformation and failure characteristics of the support column, the collaborative load-bearing mechanism of the composite column was analyzed, and the ultimate failure points of different types of composite columns were determined. Consequently, axial ultimate load-bearing capacity calculation formulas for grout-lifted compressible GFRP tube concrete composite support columns and compressible GFRP-steel tube concrete composite support columns were derived. These formulas predict the load-bearing capacity of composite support columns in roadway along gob applications, providing theoretical guidance for engineering applications.