Flexural behavior of circular concrete-filled steel tube members reinforced with annular stiffener

This paper presents a study on the flexural performance of a novel concrete-filled steel tube (CFST) member reinforced with an internal annular stiffener. The annular stiffener is composed of curved steel plates, and the circumferential plate serves as the interface connector. Four-point bending tests were conducted on the four new composite beams and two traditional CFST counterparts to investigate the flexural performance of the composite members. The failure modes, deflection distribution, flexural strength, strain distribution, and moment-curvature relationship were analyzed. The test results showed that the new composite members exhibited higher bending capacity and stiffness than their CFST counterparts. Then, a finite element (FE) model was established and validated using the test results to numerically investigate flexural behavior. The available design models for predicting the flexural capacities of the composite beams was compared. Design formulae considering the stiffener contributions were deduced to calculate the flexural strength of the composite beams based on the plastic-stress distribution method. It was demonstrated that the developed FE modeling appropriately simulated the structural behavior of the composite members. Parametric studies indicated that the use of high-strength concrete was inefficient. In addition, the comparison results indicated that the proposed design formulae were feasible for predicting the bending capacity of composite members.