Finite element study of bond strength between concrete and reinforcement under uneven confinement condition

It is well known that many factors affect the bond behaviour between concrete and steel reinforcement. Most of them characterize the degree of confinement, which is necessary for an appropriate determination of the bond strength and bond-slip relationship according to most extended models. Nevertheless, there are situations where the confinement is not known in advance or it can hardly be defined. That is, for example, the case of reinforced concrete under transverse pressure or tension. Under such conditions the confinement varies both longitudinally and circumferentially. This paper presents a 3D finite element approach to study the bond capacity of cases where the bond strength of the specimen is the result of the different contribution provided along the steel-concrete interface and cannot be described uniquely. A surface-to-surface contact model with frictional behaviour and debonding is used to study the influence of the local stress state at the interface. The model is able to reproduce the different failure modes (splitting or pull-out) obtained in experiments and provide a rational explanation of the influence of transverse tension.