Round-ended rectangular concrete-filled steel tubular short columns: FE investigation under axial compression

Concrete-filled steel tubular (CFST) columns with round-ends own the same advantages of typical CFST columns, besides their aesthetical appearance. The smoothness of the cross-section gives the effectiveness to resist running water impact when they are used as piers. Despite these advantages, there are limited researches on the behaviour of round-ended CFST columns. The paper investigates the behaviour of round-ended rectangular CFST (RRCFST) columns. Three-dimensional finite element (FE) models for RRCFST columns are developed using the ABAQUS software. The novelty of this FE model is the consideration of the confinement in the round-ended concrete. The existing experimental behaviour has been captured properly, compared with other previously suggested FE models. After the validation of FE models, a parametric study is generated taking into account wider parameters than those previously considered by other researchers. The results show two different axial load-strain responses based on the B/t ratios of the cross-sections. RRCFST columns with small B/t ratios are found to fail in a ductile manner with large axial strains. The failure of the columns with relatively high B/t ratios has been found to occur suddenly with a rapid reduction in the strength after reaching the ultimate load. The numerical results indicate that the brittle failure is associated with the columns formed from outer slender steel cross-sections. The FE strengths are compared with the available design model which was formulated based on limited research results. This design model is found to predict the strengths unconservatively. A new design model, providing better estimates, has been suggested at the end.