Reinforced Concrete Fiber Beam Element with Bond-Slip

This paper presents a new reinforced concrete beam finite element that explicitly accounts for the slip between the reinforcing bars and the surrounding concrete. The element formulation combines the fiber-section model with the finite-element model of a reinforcing bar with continuous slip. The section model retains the plane-section assumption, but the steel fiber strains are computed as the sum of two contributions, the rebar deformation and the anchorage slip. The model applies to any cross-sectional shape under biaxial bending and both monotonic and cyclic loads. The model theoretical framework is presented first. A sensitivity study on the monotonic and cyclic response of a reinforcing bar shows how the model traces the bar's reduced initial stiffness, bond degradation, and anchorage loss for insufficient anchorage length. Finally, comparison with an experimental test on a circular column shows that the prediction with the new model is in good agreement with the test, whereas the original fiber model with perfect bond overestimates the hysteretic energy dissipated during the loading cycles.