Structural behavior of concrete filled steel tubular sections (CFT/CFSt) under axial compression

• 64 CFST stub columns with 3 different domain parameters have been analyzed.
• Maximum axial strength increment ratios are seen in the circular sections.
• Rounded specimens have higher ductility than angular specimens.
• 15–20% differences were generally obtained between the experimental and FEM results.
• The concrete in tubes has experienced considerable amount of deformations.

In this study, compressive strength, modulus of elasticity and steel tensile coupon tests are performed to determine material properties. Sixteen hollow cold formed steel tubes and 48 concrete filled steel tube specimens are used for axial compression tests. The effects of width/thickness ratio (b/t), the compressive strength of concrete and geometrical shape of cross section parameters on ultimate loads, axial stress, ductility and buckling behavior are investigated. Circular, hexagonal, rectangular and square sections, 18.75, 30.00, 50.00, 100.00 b/t ratio values and 13, 26, 35 MPa concrete compressive strength values are chosen for the experimental procedure. Analytical models of specimens are developed using a finite element program (ABAQUS) and the results are compared. Circular specimens are the most effective samples according to both axial stress and ductility values. The concrete in tubes has experienced considerable amount of deformations which is not expected from such a brittle material in certain cases. The results provide an innovative perspective on using cold formed steel and concrete together as a composite material.