Mechanical properties of circular nano-silica concrete filled stainless steel tube stub columns after being exposed to freezing and thawing

Experimental research on circular nano-silica concrete filled stainless steel tube (C-CFSST) stub columns after being exposed to freezing and thawing is carried out in this paper. All of forty specimens were tested in this paper, including nine C-CFSST specimens at normal temperature, 28 short columns of C-CFSST for freeze-thaw treatment and three circular hollow stainless steel stub columns. The failure mode, load-displacement curves, load-strain curves and load-bearing capacity were obtained and analyzed in this paper. The main parameters explored in the test include the number of freeze-thaw cycles (N=0, N=50, N=75, and N=100), wall thickness (T=1.0mm, T=1.2mm, T=1.5mm) andnano-silica concrete strength (fc=20MPa, fc=30MPa, fc=40MPa). The result shows that C-CFSST short columns at normal temperature and subjected to freezing and thawing follow similar failure mode. The effect of freeze-thaw cycles (N) of 50 on bearing capacity of C-CFSST column was maximal, and then the influence of N on the bearing capacity of specimens was small when N reached to 75, finally the effect of N on bearing capacity of C-CFSST column was large when N reached to 100. The bearing capacity of C-CFSST columns increases with increasing wall thickness. In addition, the loss percentage of bearing capacity of specimens (fc=40MPa) for freeze-thaw treatment is maximal, and the loss percentage of bearing capacity of specimens (fc=30MPa) for freeze-thaw treatment is minimal. According to the test results, this paper proposed a formula to calculate the bearing capacity of C-CFSST short columns for freeze-thaw treatment.