3D meso-scale modelling of the interface behavior between ribbed steel bar and concrete

To explore the nonlinear bond behavior between ribbed bar and concrete, considering frictional resistance and the mechanical interlocking between rebar and concrete as well as the surface characteristic of crescent ribbed bar, a 3D meso-scale modelling approach is established. Comparisons between the simulation and experimental results indicate that the meso-scale method can provide good predictions of the interface behavior between concrete and deformed steel bar under confinement conditions. The bond failure mechanism and the propagation of internal crack of specimen were clearly studied and revealed based on the 3D simulations. Moreover, the influences of concrete strength gradation, ratio of cover thickness to bar diameter as well as stirrup confinement on bond stress-slip behavior, concrete failure mode and rebar stress were explored. The simulation results indicate that the meso-scale modelling method can well describe the bond failure process at the steel bar/concrete interface. It is found that increasing the concrete strength can delay the internal crack of the specimen and may change the failure mode of the specimen from splitting failure to pull-out failure. As concrete strength increases, the bond strength increases linearly, whereas the peak slip decreases slightly. The shape of bond stress-slip curve and the concrete failure modes are closely associated with the lateral confinements such as concrete cover thickness and the stirrup confinement. When the cover thickness and the stirrup confinement index reach a certain value, the bond failure would no longer be affected. In addition, the strain of stirrups increases continuously, the bond stress provided by stirrups increases first and then decreases.