Effect of hollow concrete sections on moment capacity of circular concrete-filled steel tube beams under pure bending

Abstract

Compared with reinforced concrete, concrete filled steel tube (CFST) has several advantages due to the mutually beneficial interaction between steel tube and concrete. A large number of studies of CFST columns have been performed, whereas those of CFST beams appear to be limited in the literature. Therefore, studies on CFST beams should be encouraged for building beam-column frame structures. When a concrete filled steel tube (CFST) beam is subjected to a bending moment, its sections are divided into compression and tension zones. An area of concrete near the neutral axis may participate limitedly in the resistance of CFST sections; thus, it can be made hollow to reduce the self-weight and cost. This paper thus investigates the effect of hollow concrete sections on the moment capacity of CFST beams. A CFST section was selected, and its fiber model was developed and verified. After that, a total of 60 sections of three diameter-to-thickness (D/t) ratios of 40.64, 53.5, and 78.2 were analysed and compared. The effect of hollow concrete sections was analysed and led to the conclusions. The results indicate that the moment–curvature curves are moderately affected by the hollow concrete sections. The results also showed that the concrete area can be made void up to 30.25% of the total area of CFST sections. The void area can be slightly increased up to 42.25% as the D/t ratio increased. The results also indicated that the concrete infill contributed 15.4%–19.8% to the capacity of CFST sections. The contribution of concrete infill to the moment capacity of CFST sections slightly increased as the D/t ratio increased. These outcomes can be useful information for structural engineers when designing circular CFST beams with hollow sections.