Bridge Engineering
JIANG Lei, LIU Yong-jian, ZHOU Xu-hong, CHEN Bao-chun, MU Ting-min, LIU Jun-ping, CHEN Hong-ming
To study long-term debonding effects in the engineering field and promote the development of concrete-filled steel tubular bridges, the interfacial performance, interfacial force transfer, and bearing capacity of concrete-filled steel tubes are reviewed from the point of material differences between steel and concrete. The mechanisms of debonding, interfacial force transfer failure, and composite action failure are explained. Novel structures called concrete-filled steel tubes with internal studs and concrete-filled steel tubes stiffened with PBL are proposed. The interfacial performance, interfacial force transfer, joint mechanical behavior, and bearing performance of these structures are reviewed to demonstrate the feasibility of achieving composite steel tube and concrete core action. The results indicate that steel and concrete have large differences in the aspects of heat conduction, shrinkage and creep, Poisson's ratio, elastic modulus, strength, cross-sectional dimensions, and forming ways. These differences constitute the primary reason for steel-concrete interface debonding, interfacial force transfer failure, and composite action failure. The interfacial bond strength results are highly scattered. Both the tangential and normal bond strengths of the steel-concrete interface are not higher than 1.5 MPa. The steel-concrete interface debonding cannot be avoided for bridges in the service stage owing to multiple factors, including hydration heat, sunshine temperature difference, concrete shrinkage and creep, axial loading, and fatigue loading. The interfacial force transfer for the different bridge systems can be divided into interfacial force transfer of members and joints. To this day, no interfacial force transfer model exists for bridges. Different types of debonding have different effects on the bearing capacity of concrete steel tubes. The spherical cap gap has the least effect followed by the partial circumferential gap. The circumferential gap has the largest effect. Regarding the concrete-filled steel tube with internal studs, it has been demonstrated that the internal studs can work as the shear connector to guarantee the interfacial performance and force transfer in the joint. In the case of the concrete-filled steel tube stiffened with PBL, it has been demonstrated that the PBLs can function as both the shear connector and stiffeners. From one viewpoint, this can guarantee the interfacial performance and force transfer in the joint. Conversely, it can enhance the buckling behavior of steel plates and the bearing capacity of members.