Finite Element Modeling of Bond-Zone Behavior in Reinforced Concrete

In reinforced concrete (RC) structures, adequate bond between the reinforcement and concrete is required to achieve a true composite system, in which reinforcing steel carries tensile stress, once concrete cracks, and concrete and reinforcing steel carry compression. Determining bond strength and required development length for shear transfer between concrete and reinforcement is an ongoing research subject in the field of reinforced concrete with advances in the concrete and reinforcement materials requiring continuous experimental efforts. Finite element analysis (FEA) provides opportunities to explore structural behavior of RC structures beyond the limitations of experimental testing. However, there is a paucity of research studies employing FEA to investigate the reinforcement-concrete bond-zone behavior and related failure mechanism. Instead, most FEA-based research associated with RC bond has centered on developing a bond (or interface) constitutive model for use in FEA that, by itself, can characterize bond-zone behavior, typically represented by the bond stress-slip displacement relationship. This class of bond models is useful for simulating the global behavior of RC structures but is limited in its ability to simulate local bond resistance for geometries and material properties that differ substantially from those used to calibrate the model. To fill this gap in research, this study proposes a finite element (FE) modeling approach that can simulate local bond-zone behavior in reinforced concrete. The proposed FE model is developed in a physics-based way such that it represents the detailed geometry of the bond-zone, including ribs on the deformed reinforcement, and force transfer mechanisms at the concrete-reinforcement interface. The explicit representation of the bond-zone enables simulation of the local concrete compression due to bearing of ribs against concrete and subsequent hoop tension in the concrete. This causes bond failure either due to local concrete crushing (leading to reinforcement pullout) or global concrete splitting. Accordingly, special attention is given to the selection and calibration of a concrete model to reproduce robust nonlinear response. The power of the proposed modeling approach is its ability to predict bond failure and damage patterns, based only on the physical and material properties of the bond area. Thus, the successful implementation and application of this approach enables the use of FEA simulation to support the development of new design specifications for bond zones that include new and improved materials.