Experimental Study on Time-dependent Behavior of Concrete Filled Steel Tubes in Ambient Environment

The time-dependent behavior of Concrete Filled Steel Tubes (CFST) is greatly influenced by concrete creep and shrinkage. The temperatures in ambient environment would accelerate or decrease this process. However, influence of temperatures on timedependent behavior was not considered in the references. In this paper, the shrinkage and creep tests of plain concrete and CFST in ambient environment was carried out. And CEB10 model was modified to fit to all the test results of plain concrete. Based on Age- Adjusted Elastic Modulus (AAEM) method and step-by-step method, the numerical model to calculate the time-dependent behavior of CFST considering the confining stress effect was established and compared with the methods reported in the literatures. The parametric study was conducted based on the creep models considering temperatures effect and formulas developed in this paper. The creep coefficient ratios between CFST and plain concrete in ambient conditions were carried out. The analyses have shown that the fully bond assumption between the core concrete and steel tube is valid. The proposed methods can be used to calculate the timedependent behavior of CFST accurately. Parametric analysis demonstrates that the CEB10 model considering the temperature effect has more effectiveness than other creep models used in calculating creep of CFST. Additionally, the ratios of creep coefficients between concrete and CFST are in the range of 0.2-0.6. It indicated that the time-dependent behavior of CFST influenced by temperatures should be given more attention.