Experimental behavior of CFST stub columns after being exposed to freezing and thawing

The behavior of concrete-filled steel tube (CFST) stub columns after being exposed to freezing and thawing is experimentally investigated in this paper. Thirty CFST stub columns, including 15 circular specimens and 15 square specimens, were tested, and the failure pattern, load versus deformation relationship, ultimate strength and elastic modulus of the specimens were obtained and analyzed. The number of freeze–thaw cycles (from 0 to 300) and the steel ratio (cross-sectional area ratio of steel to concrete, from 0.085 to 0.176) were considered as main parameters. The test results showed that, in general, the CFST stub columns without being subjected to freezing and thawing performed a better property than those after freezing and thawing exposures. Furthermore, the larger the number of freeze–thaw cycles, the lower the ultimate strength and elastic modulus of the CFST stub columns. Based on the regression of the test data, the simplified formula for ultimate strength and elastic modulus of CFST stub columns after being exposed to freezing and thawing was proposed, and the accuracy of the formulae was evaluated by comparison between the calculated and experimental results.