Performance evaluation of composite concrete-filled steel tube columns by steel fibers and different cross-section shapes : experimental and numerical investigations

Increasing the load-bearing capacity of columns without increasing their dimensions has become an essential issue for engineers. Concrete-filled steel tube (CFST) column is one of the common techniques used in different constructions. This study aims to assess the influence of steel fibers (SF) on the uniaxial performance of CFST columns to improve their behavior. 27 specimens are produced and tested under a uniaxial compressive load. Specimens are made with three cross-section shapes: circular, rectangular, and octagonal. Also, steel fibers are added at the three-volume percentages of 0%, 1%, and 2%. Low, normal, and high-strength concrete is used to manufacture concrete columns to consider the influence of compressive strength. The bearing capacity, load-axial shortening curves, and axial-hoop strain performance of columns are measured. Also, the obtained outcomes are compared with the requirements of current design codes and previous models. Based on the obtained results, new models are developed to predict the uniaxial bearing capacity of CFST columns with different concrete core compressive strengths, cross-section shapes, and SF contents. The results indicated that adding SF led to changing the softening behavior of the column to the hardening behavior due to raising the axial compressive strength of the concrete core. Nonetheless, this impact is more significant in CFST columns with octagonal and square cross-section shapes. Additionally, the proposed formulas in this study, with high accuracy, could be employed to predict the uniaxial bearing capacity of CFST columns with different concrete core compressive strengths, cross-section shapes, and SF contents.