Experimental study on axial mechanical behavior of reinforced concrete-filled circular steel tubular short columns after exposure to high temperatures.

Fourteen reinforced concrete-filled steel tubular (RCFST) short columns were heated following the ISO 834 standard fire condition including cooling phase, of which two specimens were used to measure cross-sectional temperatures, and the others were loaded to failure after cooling to room temperature. The temperatures of the typical cross-sections during the fire exposure, and the axial load versus displacement curves, were measured. Effects of heating time and reinforcement ratio on the residual load-bearing capacity, compressive stiffness and ductility coefficient were discussed. Six more RCFST short columns, unexposed to fire, were tested as comparative specimens to identify the effects of fire on the residual properties. Finally, a design formula was proposed for predicting the residual load-bearing capacity of RCFST columns after exposure to high temperatures, based on relevant codes or technical specifications. The study reveals that the RCFST short columns have high bearing capacity and good ductility, even though after fire exposure. Heating time has more significant effects on the compressive stiffness and ductility than the load-bearing capacity. The load-bearing capacity, the compressive stiffness and ductility after exposure to temperatures increase with the increase of ratio of reinforcement. The results predicted by the design formula were in good agreement with the test results and lie on the safe side. [ABSTRACT FROM AUTHOR]