Distributions of Stress and Strain in Concrete Filled Steel Tube Beams

Concrete filled steel tube (CFST) beams have been limitedly explored, hindering the construction of CFST frame structures. This study numerically explored the distributions of stress and strain in CFST beams under bending. A finite element model of a tested square CFST beam was developed in ABAQUS software. The CFST beam model was verified with the experimental and numerical results performed by other researchers. The verified model was then used to investigate the distributions of stress and strain in concrete and steel tubes of CFST beams. The finite element results showed that only a small portion of concrete on the top of the section participated in resisting the compression force, whereas a large portion of concrete on the bottom was cracked and did not participate in resisting the tension force. In contrast, the strain distribution in steel showed that the steel resisted both compression and tension forces on the section. Therefore, steel tubes govern the mechanical properties and behaviour of CFST beams. It can be noted that the infill concrete indirectly affected the mechanical properties and behaviour of CFST beams by providing conditions for steel tubes to work effectively. The highest stress at midspan showed that failure can occur at the midspan of the beam, although the region between the two loads has a constant bending moment and zero shear force. The outcomes provide some technical information on stress and strain distributions for structural engineers when designing CFST beams.