Residual Strength of Steel-Reinforced Concrete-Filled Square Steel Tubular (SRCFST) Stub Columns After Exposure to ISO-834 Standard Fire

Steel-reinforced concrete-filled square steel tubular (SRCFST) column has been acknowledged as a progressive form from the steel–concrete composite system, having a higher load-bearing capacity. Aiming at lying the foundations for SRCFST full-scale research after fire exposure, this paper has studied the axial compression behavior of SRCFST stub columns after different modes of fire exposure. To start with, temperature distributions, failure patterns and load–strain relationships of four existing SRCFST columns were experimentally analyzed. Based on this, numerical models of square SRCFST columns with sufficient correctness and effectiveness were established for further holistically examining impacts of fire duration time, yield strength of steel tube, compressive strength of concrete, confinement index, section steel index and sectional dimensions on residual strength of SRCFST columns. The results indicate that residual strength of square SRCFST columns decrease significantly with fire duration time, sectional dimensions and section steel index, while yield strength of steel, compressive strength of concrete and confinement index exert negligible effects. Afterwards, predictive formulas that can calculate residual strength index of square SRCFST columns under different patterns of fire exposure were proposed.