Fire performance on steel-reinforced concrete-filled steel tubular columns with fire protection

Steel-reinforced concrete-filled steel tube (SRCFST) is widely used as an innovative composite structure to provide better performance in construction. This study focuses on comprehensive experimental and numerical investigations of the fire performance of SRCFST columns with fire protection under the ISO-834 standard fire test procedures. The fire resistance tests were conducted on eight SRCFST columns with various thicknesses of fire resistive coating. The fire test results, including the thermal conductivity of protection material, failure modes, temperature evolution in time, axial and lateral deformation curves, and fire resistance were reported in detail. The results demonstrated that fire protection delayed the degradation of bending stiffness and significantly increased the fire resistance. Further comparisons of fire resistance between SRCFST columns with and without fire protection indicated that the fire resistance of SRCFST column with protection thickness of 12 mm is 3.32 times higher than that of that without fire protection under an equal load level. A sequentially coupled thermal-stress finite element (FE) analysis model was develped and validated against the tested results. The measured thicknesses of fire resistive coating were compared with the predicted results to evaluate the applicatibility of the existing design method of concrete-filled steel tubular (CFST) columns to SRCFST columns with thick fire-resistive coating. The results indicated that the current design method should be adjusted or modified further to provide safe and accurate predictions of the thickness of fire protection for SRCFST columns.