Study On The Bond Properties And Internal Force Distribution Of Concrete-Filled Steel Tubes

The bond strength and the bond properties at the interface between the steel tube and the core concrete of concrete-filled steel tubes (CFST) is a focused problems which has attracted the attention of more and more researchers. Binding completely at the interface between the two parts is the foundation of the cooperative work of the steel tube and the core concrete.Researchers had assumed there were enough bonding force between the steel tube and the core concrete, but with the development of the studies, more researchers have found that the natural bonding force is not always big enough to ensure the completely transmitting between the two parts. Further more, the application of high strength concrete also makes it is not suitable to continue following this assumption.In this paper, axial compression test of CFST is carried out, including 9 push- out tests, 4 joint tests and 4 push-off tests. Based on the results of experiment, the influencing factors of the bond strength and the differences of Internal Force Distribution under different loading methods are discussed. The ultimate transmitting length of the bonding stress of CFST is analyzed, and the calculation formula of the ultimate transmitting length considering several factors is established. At last, the influence of external stiffening ring on CFST is discussed. Suggestions on the design of CFST are given.