Fire Resistance of Concrete-Filled High-Strength Fire-Resistant Steel Tubular Columns

Fire-resistant steel has high strength at elevated temperatures, which can be applied in concrete-filled steel tubular (CFST) columns to effectively improve fire resistance and reduce or exempt fire-protective coatings. In order to investigate the fire-resistant behavior of concrete-filled fire-resistant steel tubular columns, four full-scale fire-resistant steel Q460FR CFST columns with different cross-sectional dimensions and thicknesses of cementitious coatings as well as a conventional structural steel Q460C CFST column were designed and tested under the ISO 834 standard fire condition with varying axial compression ratios. A combined numerical simulation method was proposed for calculating the fire resistance of columns, including a finite element method established by ABAQUS for simulating the temperature field and a numerical integration method based on MATLAB for calculating the bearing capacity of CFST columns at elevated temperatures. The influences of the cross-sectional dimensions, axial compression ratio, slenderness ratio, and thickness cementitious coatings on fire resistance are evaluated. Design tables and calculation formulas related to the thickness requirement of cementitious coating of fire-resistant steel CFST columns are proposed. The Q460FR CFST columns show an average of 50% higher fire resistance than Q460C CFST columns with the same thickness of fire-protective coating. Under favorable conditions of low load ratio, small slenderness ratio, and large cross-sectional size, no coating is required for CFST-fire-resistant steel columns, while it is required for CFST-conventional structural steel columns.