Experimental study on creep behavior of high-strength concrete filled steel tubular (HSCFST) columns

The use of High Strength Concrete Filled Steel Tube (HSCFST) members has become widespread, but there is limited research on their creep behavior. This study examines the creep and shrinkage characteristics of HSCFST columns subjected to axial loading by testing fifteen specimens with various steel ratios over a period of 365 days. The experimental data is then compared to the predictions made by the creep prediction models MC 90, ACI 209, and AFREM. The results indicate that the creep coefficients of HSCFST specimens are significantly lower than those of plain concrete specimens. By the end of 365 days, the creep coefficient of plain concrete is more than twice that of concrete in HSCFST. The steel ratio has a slight effect on the creep of CFST specimens, with the creep coefficient decreasing as the steel ratio increases. The comparison of the results shows that the MC 90 and ACI 209 models overestimate the creep of concrete, while the AFREM model underestimates it. Furthermore, the ACI 209 model is modified based on the experimental results by applying a correction factor of concrete strength, which significantly improves its accuracy and makes it suitable for predicting the creep of high strength plain concrete and HSCFST.