Calculation model of shrinkage for expansive concrete filled steel tube

The long-term test of concrete shrinkage strain for three circular columns was made in the indoor natural environment.By using the method of least squares for nonlinear regression analysis of measured data,the shrinkage mechanism of concrete filled steel tube was studied.The calculation model of shrinkage strain for expansive concrete filled steel tube was put forward based on the shrinkage mechanism of concrete filled steel tube,and the influence factors of shrinkage strain calculation model considered content of expander,strength grade of concrete,cement varieties and maintenance methods of the core concrete.The results show that expander has larger inhibition for concrete shrinkage strain in early stages(100 d) and has smaller influence in later stages.Expander has larger influence on shrinkage strain of concrete filled steel tube in early stages(300 d),the shrinkage strain of expansive concrete filled steel tube is almost stable in early stages.The shrinkage strain of concrete filled steel tube is mainly caused by self-shrinkage,and the self-shrinkage strain is about 1×10~(-4).The influence factors of shrinkage strain calculation model consider expander,strength grade of concrete,cement varieties and maintenance methods of the core concrete,and the calculation model can be used to forecast the shrinkage strain law of expansive concrete filled steel tube.