Numerical study of the behaviors of axially loaded large-diameter CFT stub columns.

Experimental researches on the behaviors of large-diameter concrete-filled steel tube (CFT) columns are quite limited because of expenses and capacity of testing equipment. Finite element (FE) technique is an alternative and efficient method if suitable models of materials are available. Many FE models have been proposed to simulate the behaviors of CFT columns. Results predicted by the existing models are generally found to agree well with the experimental results of CFT columns, the diameters of which, however, are generally <300 mm. It is uncertain whether these models are still suitable for the columns with diameters larger than 300 mm. In this paper, a unified FE model applicable to both small- and large-diameter CFT stub columns is proposed. The proposed FE model is then used to study the influence of column parameters and size on the behaviors of steel tube and confined concrete in CFT columns, based on which an ultimate strength considering size effect is proposed. It was found that the existing FE model predicts conservative results for large-diameter columns, whereas the proposed model performs well for both small- and large-diameter columns. Parametric studies suggest size effect on the behavior of confined concrete in a CFT column is more significant than that of steel tube, which, however, is mitigated due to the confinement effect resulting from steel tube when compared with that of plain concrete. Finally, the proposed ultimate strength model is found to perform well and more accurate than the existing model. • A unified finite element model applicable to both small- and large-diameter CFT columns is proposed. • Size effect on the behaviors of concrete in CFT columns is mitigated due to the confinement effect resulting from steel tube. • A reduction model of peak stress is proposed to indicate the size effect of concrete in CFT columns • An ultimate strength model of CFT columns considering the size effect is proposed for design [ABSTRACT FROM AUTHOR]