Static long-term effects in short concrete filled steel box columns under sustained loading

Concrete-filled steel columns have been extensively used over the last decade, which has been brought about by a renaissance of using structural steel in the construction of multistory buildings throughout the world. Considerable research efforts have been conducted on these column types into the short-term effects for strength. There have been extensive research programs conducted in North America and Japan, particularly in relation to seismic effects. Very limited research, however, has been conducted on the long-term performance of these columns under sustained loading. This paper will present a series of experiments undertaken to ascertain the creep and shrinkage characteristics of high-strength concrete in composite columns. Additionally, the creep and shrinkage characteristics of high-strength concrete specimens were also determined by virtue of the type of experiments conducted. These values were compared with existing experimental results. It is shown that the creep and shrinkage characteristics of concrete inside a steel column are significantly lower than those for exposed concrete. Furthermore, the static strength after long-term loading was also ascertained in this paper. A predictive model based on previously developed ACI provisions for both the service load and ultimate load behavior of the concrete specimens and the composite columns is calibrated with the experiments, and recommendations for design are suggested.