Experimental study on fire performance of multi-loaded geopolymeric recycled concrete filled steel tubular columns

Geopolymeric recycled concrete (GRC) is a newly developed green concrete material that can significantly reduce CO2 emissions and natural aggregate consumption compared to ordinary Portland cement (OPC). By filling the GRC into steel tubes, a type of environmentally friendly composite structure, called geopolymeric recycled concrete filled steel tubes (GRCFST), was developed, and the structural performance of GRCFSTs has been studied by researchers in recent years. This paper investigates the fire performance of GRCFST columns subjected to combined compression-bendingshear load cases. A series of fire resistance tests of GRCFST column specimens were designed and conducted, and the investigated parameters encompassed load case (compression, compressionbending, and compression-bending-shear), axial load ratio (0.2 and 0.4), horizontal load ratio (0 and 0.15), axial load eccentricity (0 and 50mm), recycled aggregate replacement ratio (0, 50% and 100%), and section types (circular and square). The failure modes, temperature distribution, deformation development, and fire resistance of GRCFST columns were systematically measured and analyzed. The test results revealed that the GRCFST column generally showed good fire performance. The GRCFST column exhibited flexural failure mode under compression-bending and compression-bending-shear load cases, and with the increase of load eccentricity and horizontal load ratio, the failure modes of GRCFST columns changed from overall buckling to local buckling. The influence of axial load ratio on fire resistance of GRCFST column was substantial, whereas the influence of recycled aggregate replacement ratio was minor. In addition, the square GRCFST column generally exhibited higher fire resistance compared to its circular counterpart. Based on the reported test data, refined finite element analysis of GRCFST columns under fire could be conducted in the future study.