A concrete-filled steel tube (CFT) combines the advantages of concrete and steel in construction and structural applications. However, research on the time-dependent deformation of the CFT under long-term sustained loading are still limited, particularly for stress transfer between the steel tube and concrete due to creep. This study investigated the creep behavior of CFT over a long period of 400 days. The creep and shrinkage strain of CFT was significantly lower than those of concrete that was not confined within a steel tube. The vertical strains of the steel tube and concrete core were almost identical, and it was shown that they were well bonded and acted as a composite. The vertical stress of steel increased by 32.7%, whereas the vertical stress of concrete decreased by 15.8% at 375 days. The stress transfer is notable and cannot be neglected in CFT design. Moreover, the results of creep and shrinkage were compared to prediction values of the B4 model and B4-TW model to verify their validity.

Many prediction models have been developed to address the disadvantages of creep, which is induced by aconstant load on concrete structures, such as cracks, deflections, serviceability failures, and reduced long-termperformance. However, the available models still lack accuracy in predicting the compressive creep of concrete,particularly in the case of self-compacting concrete (SCC), which differs from conventional concrete in itscomposition. Therefore, the model B4TW-SCC was calibrated using the B4 model to meet the SCC databaserequirements. The optimization of the new prediction model was carried out by evaluating statistical factors andthe weighting plan, which subdivided the 266 test curves in the laboratory database into independent variables.The developed prediction model performed better than the other models, based on both the SCC database andexperimental results in this study, which were conducted on the creep behaviour of SCC containing fly ash indifferent contents, 20% and 40% by mass of cementitious material.