Axial strength of CFST columns considering concrete age

Concrete filled steel tube (CFST) columns are used increasingly in high-rise buildings in China. During the rapid construction of high-rise buildings, concrete age is an important factor which will affect the composite axial strength. In this paper, based on the theory of elasticity, a formula is proposed to predict the composite axial strength of CFST considering the concrete age. For the most common use the parameters in the formula are simplified and calibrated by existing test results. Finally the experiments of the ultimate bearing capacity of CFST columns considering concrete age changes are carried out and the FE method is also adopted to validate the formula results. The results show that the formula can be used satisfactorily in predicting the strength of CFST columns considering concrete age.