Experimental investigation of square concrete filled stainless steel tubular stub columns after exposure to elevated temperatures

The behaviour of square concrete filled stainless steel tubular (CFSST) stub columns after exposure to elevated temperatures under axial compression is presented in this paper. A total of sixty-nine specimens were tested, including forty-eight square CFSST stub columns at elevated temperatures cooled in air, nine square CFSST stub columns at elevated temperatures cooled in water and twelve square CFSST stub columns left untreated at ambient temperature. A total of twelve square CFSST stub columns were carried out load-strain tests. The main parameters explored in the test include thickness (1.0 mm, 1.2 mm, 1.5 mm, 2.0 mm), concrete strength (C20, C30, C40), temperatures ranging from 400 °C to 1000 °C and cooling methods. This paper presents the failure modes, ultimate load-bearing capacity, load-strain curves, load versus displacement curves, initial compressive stiffness at the elastic stage and ductility of the specimens. It was found that high temperature had the greatest influence on the ultimate load-bearing capacity of the columns, and the cooling methods also had some effect on it. As the elevated temperature to which the specimens were subjected increased, the percentage of the ultimate load-bearing capacity decrease had an obvious increase and the ductility of the specimens was enhanced. The initial compressive stiffness decreased evidently as the temperature increased to 800 °C. A new failure mode was identified without visible corner crack in the specimens after exposure to elevated temperatures compared with the specimens at ambient temperature. The ultimate load-bearing capacity increased and the axial deformation versus load curves had a longer elastic stage as the concrete strength increased.