Finite element parametric study on the effect of loading rate on the bond of reinforcement in concrete

The bond behavior between concrete and reinforcing steel is examined under the influence of dynamic loading. The explicit finite element code LS-Dyna is used to conduct the three-dimensional analysis, and the results are compared with data obtained during experiments carried out in parallel. The numerical model is simulated at the rib-scale, which constitutes the most basic of all approaches. It involves explicit modelling of the geometry of the rebar ribs and the concrete keys in between with the final reaction being predominately controlled by the mechanical interaction between them. After a short description of the incorporated experimental set-ups, the numerical model and its calibration, the capabilities of the simulation are presented. They include detailed insights into the local structural phenomena with the model being able to capture stress and strain distributions as well as transversal and radial crack patterns inside the specimen with sufficient accuracy. The same code is thereupon used to execute a parametric study aiming at the investigation of the influence of varying loading rates on the results. Both dynamic impact scenarios and displacement controlled quasi-static executions are concerned. Loading rate dependent characteristics are identified, and the results are discussed with reference to strain rate independent constitutive materials, which were consistently used throughout the study in order to separate dynamic effects appearing at the material and the structural response level. The simulations indicate a tendency for increasing bond resistance with increasing loading rate that is qualitatively confirmed by the respective experimental data.